agricultural applications for pine-based biochar

Influence of Pyrolysis Conditions on

Char Properties

Bob HawkinsManaging Research Chemist

EpridaAthens, GA

Intro

Char’s ability to provide nutrientsChar’s ability to facilitate nutrient

retention/uptakeLow temperature char –

temperature range 375-500o

Sample PreparationBatch unit

Sample PreparationPilot Plant

Volatile ContentVM%

23.50%

24.50%

25.50%

26.50%

27.50%

28.50%

0 2 4 6 8

psig

PN

no steam

pine

higher temp

no vent

vent

Fixed CarbonFC%

64.00%

65.00%

66.00%

67.00%

68.00%

69.00%

70.00%

0 2 4 6 8

psig

press

no steam

pine

higher temp

no vent

vent

Total NutrientsCarbon content

55.0

60.0

65.0

70.0

75.0

80.0

PN371

PN402PN42

6SD37

8SD39

9SD418PC37

9PC40

1PC42

6PB382PB399PB426HW382HW400HW426HR387HR428

Charcoal sample ID

% C

Total NutrientsNitrogen content

0.00

0.50

1.00

1.50

2.00

2.50

PN371

PN402

PN426

SD378

SD399

SD418

PC379

PC401

PC426

PB382PB399PB426HW382HW400HW426HR387HR428

Charcoal sample ID

% N

Total Nutrients

Al B

Ca Cu

Fe K

Mg Mn

Mo Na

P Pb

Zn

Available Nutrients Available Potassium

0

200

400

600

800

1000

1200

1400

360.0 380.0 400.0 420.0 440.0

Charring temperature (deg C)

mg

/kg

01000

20003000

40005000

60007000

80009000

Pine sawdust

Pine chips

Pine bark

Oak-sapwood

Oak-heartwood

Peanut hull pellets

Available Nutrients Available Phosphorous

0.0

50.0

100.0

150.0

360.0 370.0 380.0 390.0 400.0 410.0 420.0 430.0 440.0

Charring temperature (deg C)

mg

/kg

0.0200.0400.0600.0800.01000.0

Pine saw dust

Pine chips

Pine bark

Oak-sapw ood

Oak-heartw ood

Peanut hull pellets

Available Nutrients

Available P as % of total

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

PN371

PN402

PN426

SD378

SD399

SD418

PC379

PC401

PC426

PB382

PB399

PB426

HW38

2HW

400

HW42

6HR38

7HR42

8

% o

f to

tal P

Available K as % of total

0.00%10.00%20.00%30.00%40.00%50.00%60.00%

PN371

PN402

PN426

SD378

SD399

SD418

PC379

PC401

PC426

PB382

PB399

PB426

HW38

2HW

400

HW42

6HR38

7HR42

8

% o

f to

tal K

Char pHChar pH

5

6

7

8

9

10

11

12

360.00 370.00 380.00 390.00 400.00 410.00 420.00 430.00 440.00

Temp

pH

Peanut hull pellet s

Pine sawdust

Pine chips

Pine bark

Oak-sapwood

Oak-hear twood

CECCEC

9.010.011.012.013.014.015.016.017.018.019.0

350 400 450 500

PN

+250-420

+500-850

PN-pilot

No Steam

CECCEC vs Pressure

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 2 4 6 8

PN

No Steam

Higher temp

Pine

Surface Acid ConcentrationCharcoal surface acids (Titration w ith NaOH)

0

0.5

1

1.5

2

2.5

3

300 350 400 450 500

Charcoal temperature

To

tal a

mo

un

t o

f su

rfac

e ac

ids

(meq

/g)

pine chips

Pine saw dust

Pine Bark

Hardw ood (red)

Hardw ood (w hite)

Peanut hull pellets

No Steam

Pilot plant

Char Production

Need for quick test for QA/QCUse of steam as a sweep gas shows increases in CEC and

surface acid formation

ELSEVIER PII:SOO16-2361(!Xi)OOO81-6

Fuel Vol. 75, No. 9, 1051-1059, 1996 pp. Copyright 0 1996 Elsevier Science Ltd

Printed in Great Britain. All rights reserved 0016-2361/96 %15.00+0.00

Influence of temperature on the products from the flash pyrolysis of biomass

Patrick A. Horne and Paul T. Williams Department of Fuel and Energy, The University of Leeds, Leeds LS2 9JT, UK (Received 12 May 1995; revised 27 March 1996)

Biomass in the form of mixed wood waste was pyrolysed in a fluidized bed reactor at 400, 450, 500 and 550°C. The char, liquid and gas products were analysed to determine their elemental composition and calorific value. In particular, the liquid products were analysed in detail to determine the concentration of environmentally hazardous polycyclic aromatic hydrocarbons (PAH) and potentially high-value oxygenated aromatic compounds in relation to the process conditions. The gases evolved were COZ, CO and C,-C4 hydrocarbons. The liquids were homogeneous, of low viscosity and highly oxygenated. The molecular weight range of the liquids was 50-1300~. Chemical fractionation of the liquids showed that only low quantities of hydrocarbons were present and the oxygenated and polar fractions were dominant. PAH up to MW 252 were present in the liquids; some of the PAH identified have been shown to be carcinogenic and/or mutagenic. The concentration of PAH in the liquids increased with pyrolysis temperature, but even at the maximum pyrolysis temperature of 550°C the total concentration was < 120ppmw. The liquids contained significant quantities of phenolic compounds and the yield of phenol and its alkylated derivatives was highest at 500 and 550°C. Some of the oxygenated compounds identified are of high value. Copyright 0 1996 Elsevier Science Ltd.

(Keywords: biomass; flash pyrolysis; products)

The energy potential of biomass and solid wastes has become increasingly recognized as a means to help meet world energy demand. The use of biomass has a particularly important role as an energy source in developing countries1’2. The utilization of biomass and other alternative fuel sources rather than existing fossil fuels could offer more environmentally acceptable processes for energy production and will aid in conser- ving the limited supplies of fossil fuels. The recovery of energy from biomass and solid wastes has centred on biochemical and thermochemical processes3. Of the thermochemical processes, pyrolysis has received increased interest, since the process conditions can be optimized to maximize the production of chars, liquids or gasesle3. In particular, the production of pyrolysis liquids has been investigated with the aim of using the liquid product directly in fuel applications or by

;;t;zEfj producing refined fuels and/or chemical . The solid char can be used as a fuel in the

form of briquettes or as a char-oil/water slurry, or it can be upgraded to activated carbon and used in purification processes”*. The gases generated have a low to medium heating value but may contain sufficient energy to supply the energy requirements of a pyrolysis plant.

The physical conditions of the pyrolysis of biomass, such as temperature, heating rate and residence time, have been shown to have a profound effect on the product ields and composition . High heating rates of up to lc& s-1 at temperatures < 650°C and with rapid quenching, fav&r the formation of liquid products and minimize char and gas formation; these process conditions

are often referred to as ‘flash pyrolysis’. High heating rates to temperatures > 650°C tend to favour the formation of gaseous products at the expense of liquids. Slow heating rates coupled with low maximum temperatures maximize the yield of char.

In recent years, various flash pyrolysis processes have been developed to maximize the formation of liquid products for use as fuels or chemical feedstocks. A vortex reactor process has been developed by Diebold”“. This type of pyrolKsk process is an ablative technique. Scott and Piskorz ’ have designed the Waterloo flash pyrolysis process to maximize the liquid product yield. They have used small biomass particles (< 1 mm) as the feed and high heat transfer rates with a hot fluidized bed of sand. Georgia Tech in the USA has used an entrained flow pyrolysis reactor where the biomass particles are rapidly heated by a flow of hot gases13. Vacuum pyrolysis has also been used as a flash pyrolysis technique by Roy et a1.14. The liquid product yields from all the above processes were >50 wt%, with Dieboldgl” and Scott and Piskorz11112 reporting yields of >70 wt%.

The liquid products from flash pyrolysis processes have been reported as being homogeneous and of low viscosity, and are chemically extremely complex, containing hundreds of different components’5-‘7. The chemical composition of the liquid hydrocarbons and the relation of composition to process conditions has implications for end use as a fuel or chemical feedstock. Many biomass-derived pyrolysis oils are known to contain polycyclic aromatic hydrocarbons (PAH)18-20, some of which have been shown to be carcinogenic and/

Fuel 1996 Volume 75 Number 9 1051

Influence of temperature on flash pyrolysis of biomass: P. A. Horne and P. T. Williams

n 4 S7ktyWVe -

II

Figure 1 Schematic diagram of the fluidized bed pyrolysis reactor

or mutagenic*l’**, which may have consequences for the handling of the fuel. Where the proposed end use of the liquid hydrocarbons is as a chemical feedstock, again the process conditions which optimize the formation of high-value chemicals in the liquid have economic benefits. In this context the oxygenated aromatic hydrocarbons are of particular interest. Biomass-derived oils have been shown to contain phenols’5’23 which have extensive use in the production of resins. In addition, phenolic derivatives have a high value, as they are used as flavourings in the food industry. Syringol and guaiacol are also found in significant concentrations in biomass- derived pyrolysis oils and are used in the production of biodegradable polyesters and polyethers.

In this work, a semi-continuous fluidized bed reactor was used to flash-pyrolyse a waste wood feed. The pyrolysis temperature range studied was 400-550°C as this is known to give high yields of liquid products whilst minimizing the formation of char and gases. Pyrolytic liquids derived from biomass have been analysed by a number of workers15-17, but there are limited data on the individual yields of PAH and oxygenated aromatic compounds in relation to process conditions, coupled with analyses of the gas phase and char. Therefore in this

work the pyrolysis liquids were characterized in detail in relation to process conditions, with particular reference to the contents of PAH and oxygenated aromatic compounds.

EXPERIMENTAL

Biomass The biomass used was a mixture of waste wood

shavings obtained from a woodworking company, and therefore represented a mixture of different wood types. Table 2 shows the proximate and ultimate analyses of the biomass pyrolysed.

Pyrolysis reactor The reactor system used was a fluidized bed pyrolysis

unit (Figure I). The reactor was 7.5 cm diameter x 50 cm high, constructed from stainless steel. The fluidization gas was nitrogen, preheated before entry into the reactor. The flow-rate of nitrogen was sufficient to provide three times the minimum fluidizing velocity (MFV) to the bed. The bed material was quartz sand with a mean diameter of 250 pm and a static bed depth of 8 cm. The biomass was fed to the reactor via a screw feeder and nitrogen gas stream to the top of the fluidized bed at a rate of 0.216- 0.228 kg h-l. The residence time of the pyrolytic vapours in the hot reactor was N 2.5 s at a pyrolysis temperature of 500°C. The pyrolysis vapours leaving the reactor were passed through a series of condensers. The initial condensation was provided by two stainless steel condensers which were water-cooled both internally and externally, with the catch pots for each condenser ice-cooled. There followed a series of glass condensers cooled using a mixture of solid carbon dioxide and acetone, which were used to remove any residual vapours from the gas stream. This condensation system was found to be 97% efficient in trapping volatile aromatic hydrocarbons such as toluene and 99% efficient for the condensation of water. The pyrolysis condensate from all the condensers was mixed and stored at -10°C. The water fraction of the pyrolysis liquids was separated from the organic fraction using the standard ASTM D244 and IP 29.1 methods.

Gas analysis The carrier gas stream was sampled after the

condensation system to allow for the analysis of any non-condensable gases. Analysis was carried out using gas chromatography. The gases determined were CO and H2 using a molecular sieve SA 60-80 column and CO2 using a silica column, with argon as carrier gas and thermal conductivity detection. For the determination of hydrocarbon gases up to Cs a Porisil C 80-100 column was used, with nitrogen as carrier gas and a flame ionization detector.

Table 1 Proximate and ultimate analyses (wt%) of the wood feed

Proximate analysis Volatiles 91.0 Moisture 1.5 Ash 1.5

Ultimate analysis C 45.9 H 5.12 0 46.6

Elemental analysis The carbon and hydrogen contents of the pyrolysis

liquids and char were determined using an elemental analyser. The oxygen content of the liquids and chars was found by difference.

Calor@ic value The calorific value of the pyrolysis liquid was

1052 Fuel 1996 Volume 75 Number 9

Influence of temperature on flash pyrolysis of biomass: P. A. Horne and P. J. Williams

determined by bomb calorimetry. The values reported are the gross heat of combustion at constant volume.

Oil analysis Molecular weight range. The molecular weight (MW)

range of the oils was determined using a mini-column size exclusion chromatography (s.e.c.) system which has been described previouslg4. The system incorporated two 150 mm x 4.6 mm i.d. columns with Polymer Labora- tories 5 pm RPSEC 100 A type packing. A third column of the same material was placed in line between the pump and the injection valve, to ensure pre-saturation of the solvent with the column packing material and also to avoid analytical column dissolution and hence loss of performance. The solvent used for the mobile phase was tetrahydrofuran (THF), which has been shown by Johnson and Chum25 to be suitable for the analysis of biomass pyrolysis oils. The calibration system used was based on polystyrene samples of low polydispersity in the MW range from 800 to 860000; also included was benzene for low-MW calibration. Samples were introduced through a 2 ,ul loop injection valve. Two detectors were used: a U.V. detector sensitive to the aromatic compounds, and a refractive index (RI) detector monitoring the elution of all compounds, enabling more information to be obtained regarding the relative contribution to the MW of the difference chemical class fractions24. Ultraviolet scanning of the polystyrene MW fractions in THF indicated that the maximum absorbance was at 262nm. Determination of the maximum efficiency for the system showed that a mobile phase flow rate of 0.26 mL min-’ and a column temperature between 2 and 14°C were optimum24. For practical purposes the column was maintained at 0°C. Column temperature is usually maintained at room26 or elevated temperature27-29. However, the optimum efficiency was obtained at lower than ambient temperatures for the system used in this work.

Evaluation of the system has shown that there are systematic variations in the measured MW of n-alkanes, n-alkenes, PAH and alkylated cyclic hydrocarbons compared with the polystyrene standards24. Deviations from polystyrene calibration curves have also been shown previously for other model compounds26>30>31. For biomass pyrolysis oils, Johnson and Chum25 used polystyrene MW fractions and showed that aromatic acids and naphthalenes deviated significantly from the calibration curve. However, in this work the s.e.c. system was used to compare oils derived from different process conditions rather than to determine the absolute MW.

Chemicalfractionation. The biomass-derived pyrolysis oils were fractionated using mini-column liquid chromatography. The mini-columns were conditioned by washing with n-pentane. A 250 mg sample of the oil was placed on the column. The samples were added by adsorption on to inert Chromosorb G/AW/DMCS 60-80 support, mixed and then packed above the silica section of the column. This approach is necessary for polar oils, which may produce a solid-phase precipitate with the n-pentane solvent and block the column, and also to improve solvent contact with the oil. The column was then eluted with n-pentane, benzene, ethyl acetate and methanol (polarity relative to Al2O3, 0.00, 0.32, 0.58 and 0.95 respectively), to produce aliphatic, aromatic, oxygenated- aromatic and polar chemical class fractions respectively.

The fractions were analysed by Fourier transform infrared spectroscopy (FT-i.r.) to determine the efficient separation of the chemical classes. In addition, each fraction was analysed by gas chromatography-mass spectrometry using ion trap detection (g.c.-ITD) to verify the fractionation scheme. The percentage mass in each class fraction was determined by analysis of the total gas chromatogram in relation to known masses of sample and standards analysed by the system. This avoided the necessity to nitrogen-evaporate (blow down) the solvent eluant, which may result in losses of light hydrocarbons.

Detailed characterization of the pyrolysis liquids. The concentrations of monocyclic and polycyclic aromatic hydrocarbons (PAH) in the benzene fractions and the oxygenated aromatic species present in the ethyl acetate fraction were determined using gas chromatography- mass spectrometry (g.c.-m.s.) The g.c.-m.s. system was a Carlo-Erba Vega HRGC with cold on-column injections, coupled to a Finnigan Mat ion trap detector (ITD). A DB-5 fused silica capillary column 25mx 0.3mm was used and the temperature programme was 60°C for 2min followed by 5 Kmin-’ to 270°C with a dwell time of 25 min at 270°C. The ITD mass range was set at 30-350~ with a scan time of 0.125-2 s. The ITD was linked to a PC with a mass spectral library facility. Identification of the individual constituents in the chemical fractions was carried out using the g.c.- m.s. and retention indices23,32Y33. Single-ion monitoring (SIM) was also carried out to confirm the identification of compounds and also to examine the samples for a series of substituted compounds, for example, naphthalene and methyl-, dimethyl- and trimethylnaphthalenes. Quantification was determined by the use of extensive external standards.

RESULTS AND DISCUSSION

The yields of the pyrolysis products are shown in Table 2. Several repeat runs were carried out at 550°C under identical conditions to test the repeatability of the process. The differences observed between the yields of the char, liquid and gas for these repeat runs were negligible. The liquid yield for all the runs was >65 wt%, with a maximum yield of 67.8 wt% at 550°C. At pyrolysis temperatures of 500 and 550°C the pyrolysis

Table 2 Product yields (wt%) from the flash pyrolysis of wood

Reactor temperature (“C) Char Liquid Gases Total

400 24.1 65.5 10.2 99.8 450 21.4 65.7 11.1 98.2 500 18.9 66.0 14.6 99.5 550 17.3 67.0 14.9 99.2 550 16.7 67.8 15.7 99.2 550 17.1 66.2 15.2 98.5

Table 3 Water and organic contents (wt%) of the liquid product from the flash pyrolysis of wood

Reactor temperature (“C) Water Organic material

400 28.0 72.0 450 27.6 72.4 500 29.6 70.4 550 26.8 73.2



liquid was a homogeneous dark liquid of low viscosity. Similar observations were made by Scott and Piskorz ’ using a fluidized bed process with a pyrolysis temperature of 500°C. The pyrolytic product from the 400 and 450°C fluidized bed pyrolysis temperature experiments was found to be of low viscosity but there were traces of a black tar residue on the base of the storage vial. The pyrolysis liquid product was a mixture of organic material and water. The water content of the liquid was determined using the ASTM D244, IP29.1 method; Table 3 shows the results of this separation. The water content of all the pyrolytic liquids was approximately the same (26.8-29.6wt%). The initial wood feed contained 7.5 wt% moisture, which would be released during pyrolysis and subsequently collected during condensation. This contributed approximately half the water present in the pyrolytic liquid. Therefore water formed by pyrolysis accounts for 14 wt% of the liquid condensate or lOwt% of the initial wood feed. Table 3 also shows that over the temperature range studied, the yield of oil was not significantly affected by a change in temperature.

The char yield was reduced as the pyrolysis temperature was increased, from 24.1 wt% at 400°C to 16.7 wt% at 550°C. The char yields reported in this work were higher than those found by other workers1”12. This difference was probably due to the fact that a mixed wood waste was used in this work rather than a single known biomass feedstock as used by Scott et al.11>‘2. The decrease in the char yield with increasing temperature could be due either to greater primary decomposition of the wood at higher temperatures or to secondary decomposition of the char residue.

The gaseous product yield increased with pyrolysis temperature. The individual yields of the major gaseous species are shown in Table 4. The increase in gaseous products is thought to be predominantly due to secondary cracking of the pyrolysis vapours at higher

Table 4 Yields (wt%) of gases from the flash pyrolysis of wood

Reactor teme. (“(7 L CO COP Hz CH4 C2H6 W4 C3h C3H6

400 3.75 6.02 0.018 0.21 0.05 0.05 0.03 0.05 450 4.20 6.32 0.022 0.35 0.05 0.08 0.02 0.08 500 6.76 6.61 0.022 0.58 0.09 0.26 0.05 0.19 550 6.71 6.86 0.023 0.69 0.16 0.26 0.04 0.45

Table 5 Elemental composition (wt%) of the products from the flash nvrolvsis of wood

Reactor temp. (C) C H 0

Total liquid product 400 38.6 450 39.9 500 37.6 550 38.1

Liquid product after water removal 400 58.1 450 58.0 500 57.2 550 59.6

Char 400 68.1 450 71.9 500 73.0 550 71.6

8.52 8.61 8.42 8.46

6.10 34.6 6.24 35.0 6.12 35.2 6.05 33.5

3.23 3.16 3.17 2.65

51.7 50.4 53.0 52.8

28.2 24.2 22.9 24.4

temperatures. However, the secondary decomposition of the char at higher temperatures may also give non-condensable gaseous products. Beaumont and Schwob34 and Samolada et aL3’ investigated the flash pyrolysis of wood and found that as the pyrolysis temperature was raised, the gaseous yield was increased. The yield of CO and CO2 in general increased with increasing pyrolysis temperature. However, the increase in CO was far more pronounced than that of C02. The yield of all the hydrocarbon gases increased with temperature. Similar observations have been made by other workers11’35.

Elemental analysis of pyrolysis products The liquid and char products were analysed to

determine their elemental composition. Table 5 shows the elemental compositions of the wet pyrolytic liquid, the oil after removal of water, and the chars. The elemental compositions of the pyrolytic liquids both before and after removal of water were similar for all the pyrolysis temperatures investigated. The similarity was probably due to the particular temperature range studied, the lowest temperature of 400°C being adequate to decompose the wood feed, and the low residence time limiting the amount of secondary reactions. The pyrolysis liquids arising from the reactor before water removal had a carbon content lower than that of the initial wood feed. This indicates that such pyrolytic liquids have a low CV, and the removal of the water is necessary to maximize their CV. The composition of the pyrolytic liquid produced in this work compares well with the finding of Churin36.

Characterization of the pyrolysis liquids Molecular weight range. The pyrolytic liquid after

water removal was used for determination of the MW range of the oils, because the presence of water caused the RI detector to give inconsistent results. Figure 2 shows MW ranges of the pyrolysis oils for the RI and U.V. detectors. Only the data for the 400 and 550°C pyrolysis oils are shown, for clarity. The oils all showed similar MW ranges from 50 to 1300~ for both the RI and U.V. detectors. The similarity in MW among the oils over the temperature range studied was due to the fact that the lowest temperature, 4OO”C, was sufficient to give almost complete decomposition of the wood feed and the low residence times minimized secondary reactions which might have occurred at higher temperatures. The average MW was -220 and ~275 u for the RI and U.V. detectors respectively. Diebold et a1.37 obtained flash pyrolysis oils from a vortex reactor system at 625°C. They carried out s.e.c. analysis of the oil and found components present in the oil up to and including 2000~. Evans and Milne2’ used molecular beam mass spectrometry (MB-m.s.) to analyse the pyrolysis vapours whilst in the pyrolysis reactor. They found molecular

Table 6 Chemical fractionation of the pyrolysis liquids (wt%)

Reactor Pentane Benzene Ethyl acetate Methanol temp. (“C) eluate eluate eluate eluate Total

400 <0.2 0.42 36.2 56.8 94.6 450 <0.2 0.51 37.4 57.6 95.7 so0 <0.2 0.54 39.3 56.7 96.7 550 <0.2 0.54 38.4 55.2 95.3


influence of temperature on flash pyrolysis of biomass: P. A. Horne and P. T. Williams

0 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Log Molecular Mass

(b)

b oi,4,,,, , , ‘, , ” , , ), I 16 1.6 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Log Molecular Mass

Figure 2 Molecular mass range of the pyrolysis liquid at 400 and 550°C after removal of water, using refractive index and ultraviolet detection

weights predominantly between 100 and 150 u. The difference between the findings of Evans and Milne and the present results is due to the fact that the condensed pyrolysis liquids were analysed in this work and that of Diebold et al.37. It is thought that some of the smaller species present in the pyrolysis vapours are highly reac- tive and on condensation can polymerize to form higher-molecular-weight material’.

Johnson and Chum25 have suggested that the high apparent MW of biomass pyrolysis oils may be due to solute-solute or solute-solvent association, producing high-molecular-weight complexes. In this work, the samples were prepared with THF immediately prior to analysis, since previous work has shown that storage of the sample in THF for extended periods did result in an increase in apparent MW due to interaction of the sample with the solvent3*.

The U.V. detector was used to obtain detail on the MW range of the aromatic fraction of the pyrolysis oils. It showed that there was some high-molecular-weight material present in the oils which was aromatic in nature. This could be formed from the decomposition of the lignin fraction of the wood.

The results of the chemical fractionation are shown in Table 6, corrected to account for the removal of water. They show that the liquids are almost exclusively made up of oxygenated compounds. The ethyl acetate fraction, which contains the phenolic and aromatic oxygenated compounds, shows a small but significant increase in concentration from 36.2 to 39.3 wt% of the oil as the pyrolysis temperature increases from 400 to 550°C. The polar material present in the methanol fraction of the liquids shows no significant trend with change in temperature, varying from 55.2 to 57.6 wt%. The hydrocarbons, eluted in the pentane and benzene fractions, account for < 1 wt% of the pyrolytic liquid. The benzene fraction, containing aromatic species, shows a small increase with increasing pyrolysis temperature. The similarity of the results for the chemical fractionation of the oils over the temperature range studied is again due to the fact that the fluidized bed process minimized any secondary reactions and the lowest temperature, 400°C was sufficient to give almost complete decomposition of the wood feed.

Characterization of the chemical fractions of the pyrolysis liquids

Chemical fractionation. The pyrolytic liquids after PAH content. The major aromatic hydrocarbon removal of water were separated into four chemical compounds present in the pyrolysis oils are shown in classes by sequential elution of the column with pentane, Table 7, with PAH compounds up to molecular mass benzene, ethyl acetate and methanol to give aliphatics, aromatics including PAH, phenolic and neutral oxyge-

252 identified and quantified. The major aromatic hydro-

nated compounds, and polar compounds respectively. carbons present in the pyrolysis liquids were the monocyclic compounds such as benzene, toluene and

Table 7 Concentrations (ppmw) of the aromatic compounds present in the pyrolysis oils

Reactor temperature (“C)

400 450 500 550

Benzene 7 14 55 97 Toluene 5 12 35 6-l Dimethylbenzene 1 1 2 I Ethylbenzene 2 2 7 24 Dimethylbenzene 1 1 3 12 Trimethylbenzene 5 5 7 9 Dihydroindene <l <l <l 4 Indene 2 3 6 2 Benzofuran 1 2 4 10 Methylbenzofuran 3 2 5 13 Tetramethylbenzene <l <l <l <l Methylindene <l <l <l 2 Naphthalene 3 5 4 11 Methylnaphthalene 3 4 9 14 Biphenyl 1 1 1 2 Acenaphthene <l 1 1 3 Dimethylnaphthalene 3 5 9 15 Trimethylnaphthalene <l 3 5 7 Tetramethylnaphthalene <l <l <l <l Fluorene <l <l 1 1 Methylfluorene <l <l 1 <l Phenanthrene 3 5 6 11 Anthracene 2 2 4 6 Dimethylfluorene <l <l <l <l Methylphenanthrene I I 10 16 Dimethylphenanthrene 3 I 8 12 Trimethylphenanthrene <l 1 1 2 Tetramethylphenanthrene <l <l <l 2 Pyrene <l <l <l 1 Methylpyrene <l <l <l <l Dimethylpyrene <l <l <l <l Chrysene <l <l <l <l Methylchrysene <l <l <l <l Benzopyrene <l <l <l <l


influence of temperature on flash pyrolysis of biomass: P. A. Horne and P. T. Williams

dimethyl- and ethylbenzenes. The PAH found were naphthalene and phenanthrene and their alkylated derivatives and in minor concentrations other compounds such as pyrene, chrysene and benzopyrenes. The concentration of PAH increased with increasing temperature. The PAH found have been shown to be carcinogenic and/or mutagenic2113g@. However, even at the highest temperature of 550°C the total concentration of PAH quantified was < 120 ppmw.

PAH have been detected by other workers in biomass pyrolysis oils. For example, Pakdel and Roy41 analysed oil from the pyrolysis of Aspen poplar wood chips in a vacuum pyrolysis unit. They found a wide range of PAH including naphthalene, phenanthrene and fluorene and their alkylated substituents, in addition to benzene and its alkylated substituents. In addition, they quantified certain PAH, some of which were biologically active, such as benzo[a]pyrene, chrysene and benzo[k]fluor- anthene, but were present in very low concentration, <5ppmw. However, the oil was collected at a biomass pyrolysis temperature of only 263°C. Gasification tars, produced at higher temperatures (XSO’C) than the pyrolysis oils, were found to contain much higher concentrations of PAH. However, the yield of gasification tar was small relative to that of the biomass pyrolysis oils. Elliottlg has also confirmed that PAH are not present in pyrolysis oils produced at temperatures <5OO”C but markedly increase in concentration in gasification tars produced >7OO”C. Desbene et ~21.‘~ analysed pyrolysis oils from the slow pyrolysis of hornbeam biomass. The PAH detected included alkylated naphthalenes, biphenyls, fluorene, anthracene, pyrene and benzofluorene. The composition of the oil depended on whether the pyrolysis was slow or fast. The low concentrations of PAH in the pyrolysis oils in the present work are due to the process conditions used. The relatively low temperatures and residence times restrict the formation of PAH by reducing the amount of possible secondary reactions. For significant quantities of PAH to form during the pyrolysis of biomass, long residence times are needed at temperatures >700”C20.

Table 7 shows that as the temperature of pyrolysis was increased, the concentration of PAH in the oils also increased. For each individual PAH there was an increase with increasing pyrolysis temperature. The reactions of the pyrolysis vapours at increased temperatures result in the formation of PAH. The formation of aromatic and polyaromatic hydrocarbons by secondary reactions during pyrolysis has been attributed to at least two mechanisms: a Diels-Alder type reaction, and deoxy- genation of oxygenated aromatic compounds42.

The calorific values of the pyrolysis liquid after removal of water, the char and the

g ases from the

550°C run were found to be 22MJ kg- , 25.9 MJ kg-’ and 15.7 MJ me3 respectively. The original wood feed had a CV of 17.7 MJ kg-‘. Therefore the pyrolysis liquid after removal of water contained -63% of the potential energy in the wood feed. The density of the pyrolytic liquid (1.2 g cme3) was also much greater than that of the initial feed (0.4 gcmp3), giving a much higher energy density. There was a significant amount of water present in the pyrolytic liquid which would significantly reduce its CV. Indeed, the elemental analysis shows that the pyrolysis liquid before removal of water contains significantly less carbon than the original biomass. However, removal of the water may not be beneficial,


as the liquid product from the flash pyrolysis of wood has been shown to be unstable at elevated temperatures and polymerizes when exposed to air37. The viscosity of the pyrolytic liquid may also be increased by removing the water, which could affect its use as a fuel.

There are conflicting opinions as to the potential uses of pyrolytic liquids derived from biomass. Maggi et aI.43 state that flash pyrolysis bio-oils are corrosive, are not completely volatile, have a high oxygen content and do not mix readily with conventional fuels. They state that bio-oils used in direct combustion processes rarely meet the standards required for fuels. Rapper questions whether pyrolysis liquids meet the requirements of a storable liquid fuel, and states that pyrolysis oils are much lower in quality than even a heavy fuel oil, which itself has a rapidly shrinking market. However, Bridgwater45 has suggested various processes where flash pyrolysis liquids could be used both now and in the future. Many of the processes that he suggests require the pyrolysis liquids to be refined or upgraded before they are suitable for use. Solantausta et a1.46 used flash pyrolysis oils as a fuel in a diesel power plant. They concluded that the preliminary results were positive but that further research was necessary on the storage of the oils and that the oils themselves required more detailed characterization. More detailed characterization of the pyrolysis oils is necessary to optimize their potential. The PAH content of any fuel is of great importance, as these compounds are environmentally hazardous and therefore their concentration in a fuel should be minimized. The process conditions used in this work show that flash pyrolysis gives only low levels of PAH formation from biomass feedstocks.

Ethyl acetate fraction. The major compounds present in the ethyl acetate eluates of the pyrolysis liquids were identified and quantified; the results are shown in Table 8. The major constituents of the eluate appear to be light organic oxygenates and phenolic material. The major phenolic compounds present in the ethyl acetate eluate of the pyrolysis liquid were phenols, benzenediols, meth- oxyphenols and dimethoxyphenols. The concentration of phenol and its alkylated derivatives increased as the pyrolysis temperature was increased, but 500 and 550°C gave similar yields. The formation of methoxyphe- no1 and its mono- and dimethyl derivatives was greatest at the lower pyrolysis temperatures. This was also true for the overall concentration of dimethoxyphenol and its derivatives. The more severe pyrolysis temperatures of 500 and 550°C would increase the possibility of secondary reactions that could be responsible for the thermal breakdown of the larger phenolic compounds such as methoxy- and dimethoxyphenols to phenol, which would then undergo alkylation, thus giving the increase in alkylated phenols observed at 500 and 550°C.

The ethyl acetate fraction also contained large amounts of methylmethoxy-, dimethoxy-, hydroxy- methoxy- and dihydroxymethoxyphenylethanones. The concentration of these compounds in the pyrolysis oils varied, depending on the pyrolysis temperature. The other major group of compounds present in this fraction comprised cyclopentanone, cyclopentenone and the methyl and hydroxymethyl derivatives of cyclopentenone. The concentration of these compounds in the pyrolysis oils increased as the pyrolysis temperature was increased. There were large amounts of light organic


compounds such as glycol aldehyde and the propyl ester of acetic acid, which were greatest in the pyrolysis oil produced at 450°C. Other light organics present in the oils were furanmethanol, furanone and methylfurfural. The concentration of these compounds in general increased with pyrolysis temperature.

In the work the biomass pyrolysis liquids have been shown to contain significant quantities of phenolic compounds. These phenolic compounds could be removed from the pyrolysis liquids prior to their combustion, as they have a significant commercial value47148. The use of the pyrolysis liquids for the

production of phenolic chemical feedstocks as well as for the production of liquid fuels would increase their potential commercial exploitation. In maximizing the formation of individual phenolic compounds, it must be taken into account that an increase in pyrolysis temperature in this work tended to increase the formation of phenol and its alkylated derivatives whilst reducing the formation of the larger phenolic compounds. Stoikos48 has reviewed the upgrading of biomass oils to high-value chemicals and premium-grade fuels. He reports that oxygenated compounds such as methylphenols (cresols), methyoxyphenol (guaiacol),

Table 8 Concentrations (ppmw) of the major constituents in the ethyl acetate eluate of the flash pyrolysis oils

Reactor temperature (“C)

400 450 500 550

MW 60 (acetic acid methyl ester or glycol aldehyde) 11876 13211 12874 12000

Acetic acid propyl ester 13214 17656 14901 15710

Cyclopentanone 2231 2310 2415 2380 Cyclopentenone 4645 4650 5315 5580

Furanmethanol 2641 2460 2412 2467

Methylcyclopentenone 610 742 898 845

Furanone 7178 8141 9542 10024

Methylfuraldehyde 0 0 0 2308

Methylcyclopentenone 0 0 0 681

Phenol 937 1073 1992 1839

Methylhydroxycyclopentenone 1987 2143 2101 2470 Methylphenol 779 1213 2215 2261

Methoxyphenol 3373 3657 2892 2930

Dimethylphenol 116 149 430 436

Methylmethoxyphenol 206 177 143 1412

Benzenediol 3432 3771 3730 4028

Methylbenzenediol 715 1313 2379 2675 Trimethylphenol 0 0 408 229

Tetramethylphenol 0 0 0 0 Dimethylmethoxyphenol 1317 1021 954 750 Hydroxymethylphenylethanone 3003 2974 2854 3097 Dimethoxyphenol 3756 3720 4120 4261 Ethenylbenzenediol n/a nla nla 1414 Methoxypropenylphenol 2711 2881 3214 3542 MW 168 (unidentified) 4271 3297 3365 3252 Methoxypropenylphenol 6645 6525 4974 4511 Hydroxymethoxyphenylethanone 1316 1723 1721 1775 Dihydroxymethoxyphenylethanone 1190 1303 1021 807 Hydroxymethoxyphenylpropanone 895 1074 876 913 MW 180 (unidentified) 3134 3017 4521 5246 Dimethoxypropenylphenol 2381 2751 2552 2257 MW 180 (unidentified) 597 703 515 465 Hydroxydimethoxybenzaldehyde 1695 1723 2195 1669 Hydroxymethoxypropenylphenol 7660 8305 8778 9203 Dimethoxypropenylphenol 5834 5520 4874 4948 Hydroxydimethoxyphenylethanone 1019 1071 1066 1026 MW210 (unidentified) 641 607 688 906 MW210 (unidentified) 1444 1861 2154 3146 Naphthol 33 40 65 54 Methylnaphthol 66 70 99 116 Dimethylnaphthol 0 0 0 0 Trimethylnaphthol 0 0 0 0



2-furaldehyde (furfural) and methoxypropenylphenol (isoeugenol), which have been shown to be in high concentration in the oils (Table 8), have a considerable economic potential. Such chemicals have applications in the pharmaceutical, food and paint industries.

CONCLUSIONS

The formation of pyrolytic liquid products derived from biomass can be maximized using a fluidized bed reactor coupled with moderate temperatures of 400- 550°C and short residence times. The pyrolysis temperatures of 500 and 550°C gave a pyrolytic liquid product which was homogeneous and of low viscosity. The pyrolytic oil was found to contain material with a molecular mass of up to 1300 u. Chemical fractionation showed that the pyrolytic liquids were composed almost entirely of oxygenated components, with only low quantities of hydrocarbons present. The analysis of the ethyl acetate eluate from the chemical fractionation of the pyrolytic liquids showed that the oils contained significant quantities of oxygenated aromatics, mainly phenol and its derivatives. The concentration of phenol and its alkylated derivatives was greatest at 500 and 550°C whereas the concentration of the larger phenolic compounds was greatest at lower temperatures. Some of the phenolic compounds present have been shown to have a significant commercial value. PAH up to molecular mass 252 were found to be present in the pyrolytic liquids. The concentration of PAH was increased with temperature, but the overall PAH concentration in all the pyrolytic liquids was low. The pyrolytic liquids were found to have a relatively low CV, but they contained -63% of the potential energy in the initial biomass feed and had a much greater density than the original biomass.

ACKNOWLEDGEMENTS

This work was supported by the UK Science and Engineering Research Council under grant numbers GR/F/06074 and GR/F/87837, whose support the authors gratefully acknowledge.

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UTILIZATION OF BIOMASS PYROLYSIS FOR ENERGY PRODUCTION, SOIL FERTILITY AND CARBON SEQUESTRATION

ROBERT HAWKINS, JON NILSSON AND REBECCA OGLESBY (for authors correspondence, E-mail: [email protected])

Abstract. New pyrolysis technologies have been developed that allow for carbon sequestration through the production of sustainable energy from biomass (bioenergy). These systems produce charcoal (biochar) and energy in the form of heat, steam, electricity, or liquid fuels. Purified hydrogen can also be produced, allowing production of ammonia and future electric systems that utilize hydrogen (such as hydrogen fuel cells). Pyrolysis energy systems produce more power than they consume, and can supply their own power utilizing waste heat from the system. Therefore, this technology could be deployed without the need for existing energy infrastructure. The biochar is a carbon-based co-product that has value as a soil amendment, containing nutrients such as potassium (K), phosphorous (P), magnesium (Mg) and calcium (Ca). When placed in the soil, an increase in soil organic matter (SOM) is observed, along with increases in crop productivity, water retention, and soil biological activity as well as a decreased fertilizer requirement. Pyrolysis technology can be deployed on a large industrial scale, or on small farm or community scales. In these applications it can produce fuel, heat, electricity and fertilizer from crop residues and wastes. The deployment of new biochar and bio-energy systems creates economic opportunities for local communities through the creation of new businesses that develop to support its infrastructure (suppliers of bio-wastes, manufacturer and distribution of co-products, and related agricultural application services etc.). Due to its adaptability to a wide range of feedstocks, over 60 organizations are now involved in biochar research worldwide.

Figure 1. Concept of low-temperature pyrolysis bio-energy with biochar sequestration. Typically, about 50% of the pyrolyzed biomass is converted into biochar and can be returned to soil. (Adapted from: Lehmann, J. 2007, Bioenergy in the black. Front Ecol Environ 2007; 5(7): 381–387)

Transport Energy Coproducts Industry

Biomass - manure - organic wastes - crop residues - wood waste

Returned to soil as bio-char

Optionally, N2, NOX, SOX, CO2 can be added to increase C sink and nutrient content

Pyrolysis

Biofuel bio-oil hydrogen

Residual Heat

Biomass Pyrolysis Technology

At the 2007 United Nations Commission on Sustainable Development, a new system of converting biomass to energy was presented which can reduce dependence on oil. This technology is called biomass pyrolysis. In this system, biomass is exposed to high temperatures in the absence of oxygen, producing energy and co-products. Although pyrolysis biofuel production represents only a small portion of energy production worldwide (UNDP 2004), it has the potential to generate electricity at a cost lower than any other biomass-to-electricity technology available (Bridgewater et. al. 2002). A main advantage to implementing this technology is that a pyrolysis system can supply its own power and heat by utilizing waste heat from the system, so there is no need to supply power or heat from outside sources (Iwasaki, 2003). Therefore, these systems can be deployed without the need for existing energy infrastructure. With these new advances, well over 15 countries are now involved in commercializing biomass pyrolysis systems (http://terrapreta.bioenergylists.org/company). A number of companies are working on making this technolgy more scaleable to agricultural industries with various sizes of pyrolysis units. With these new designs, it is estimated that a 1-ton of biomass per hour unit can produce 1 mw of electricity, 1 megawatt of usable heat and 600 pounds of charcoal per hour. A unit capable of processing 25kg of biomass is estimated to produce 25 kw of heat and electricity and 20 pounds of charcoal per hour.

The EPRIDA pyrolysis plant that operated at the Biomass Conversion Center in Athens, GA. until spring of 2009.

Biomass Pyrolysis vs. Conventional Biomass to Energy Systems

In conventional use of biomass for fuel, biomass is harvested and burned, and like fossil fuels, releases compounds back to the atmosphere. This contributes to increased greenhouse gases. In order for the energy cycle to be truly carbon neutral, an amount of biomass equal to that which was harvested must be re-grown so that the plants can absorb an equivalent amount of CO2. To be a steady fuel supply, biomass crops require an increase in agricultural production, which further depletes soil nutrients and minerals. This reduces the ability to grow biomass in the future. Therefore, although biomass crops are a renewable source of energy, they are not necessarily sustainable. With biomass pyrolysis, what was previously considered agricultural waste (crop residues, wood wastes, manures) can create energy and nutrient enhancing soil supplements. The energy created can be converted into several forms including hydrogen and electricity, which can be used to power small farms or fed back onto the energy grid. Examples of feedstocks include: coconut husks, corn stover, bean stubble, tobacco stalks, wastes from agricultural processing, wood wastes from manufacturing and lumber industries, demolition wood wastes,

short-rotation energy crops, municipal solid waste, manure and sewage (Antal 1982). By using agricultural wastes, biomass pyrolysis does not compete with food production. The Products of Biomass Pyrolysis

The main products generated by biomass pyrolysis are pyrolysis vapors, heat and charcoal (biochar). These outputs can be used in a wide range of applications. 1. Pyrolysis vapors can be condensed to form bio-oil Bio-oil is a complex mixture of oxygenated hydrocarbons and water that can be used as low grade heating fuel. Due to its high density, bio-oil is much more economical to transport than either biomass or hydrogen (Czernik et al., 2007). The heating value of bio-oil is about 40% to 50% of that for petroleum-based fuels (Yaman, 2004) and about 60% of ethanol (Raveendran et al., 1996). Bio-oil can be refined to be used as a source of chemical feedstock for gasoline, can be added to petroleum refinery feedstock or combusted in raw form (Samolada et al., 1998). Biomass pyrolysis allows biomass to be processed at dispersed locations where wastes are generated and bio-oil can be transported to a central refinery or power plant. Cost benefits are significant due to the high price of transporting biomass feedstock over large distances (>30 km). Decentralized production of bio-oil also makes sense since biomass is often generated in rural areas where bio-oil can be processed for use in agricultural machinery. 2. Pyrolysis vapors can be used directly for energy In this scenario it is not necessary to condense pyrolysis vapors into bio-oil to extract the energy. Pyrolysis vapors can be burned directly as fuel for integrated heat and power production, or refined to produce fuels and chemicals such as gasoline, diesel, alcohols, olefins, oxychemicals, synthetic natural gas and high purity hydrogen (Magrini-Bair and others, 2007). If the energy is needed for local use, such as on a small farm, it is better to work with the pyrolysis vapors in this form. 3. Pyrolysis vapors can be treated to produce synthetic gas (syngas) Utilizing steam reforming, pyrolysis vapors can produce a syngas consisting of over 50% hydrogen, plus CO, CO2, and small amounts of methane (Czernik et al., 2007). Since these gases are comprised of hydrocarbons, they should not be emitted into the atmosphere in an unaltered state. Instead they can be converted into a clean burning, mid BTU fuel, similar to natural gas. This can be combusted in existing engines, generators, boilers, and turbines to produce heat, steam and electricity. Syngas is also suitable as a cooking fuel and can substitute for propane or natural gas in uses such as home heating. High purity hydrogen from syngas can be suitable for use in hydrogen engines, fuel cells (Czernik et al., 2007) and for production of ammonia fertilizers. The current largest use of hydrogen in the world today is for the production of ammonia. Utilizing pyrolysis to generate hydrogen could replace natural gas as the primary feedstock required to manufacture ammonia based fertilizers. The production of ammonia using natural gas emits carbon dioxide into the atmosphere and fixes the price of fertilizer to the price of natural gas. Production of ammonia from syngas could change this, allowing the price of fertilizer to become influenced by the lower price of biomass wastes. 4. Pyrolysis syngas can create synthetic liquid fuels Pyrolysis of biomass is one of the leading near-term options for renewable production of hydrogen and has the potential to provide a significant fraction of transportation fuel required in the future (Czernik et al., 2007). This can be achieved by use of hydrogen fuel cell vehicles or hydrogen powered combustion engines. Pyrolysis syngas can be used to produce transportation fuels that work with current infrastructures and technologies. Hydrogen and carbon monoxide, main components of the pyrolysis syngas, are the reactants necessary to produce liquid fuels (methanol, ethanol, gasoline, aviation fuel and diesel fuel) via Fischer-Tropsch (F-T) synthesis. F-T synthesis is regarded as the key technological component for converting syngas to transportation fuels and other liquid products (Wilhelm and others, 2001). F-T diesel is not bio-diesel. FT diesel is a clear liquid that gives complete combustion with no particulate emissions and has a higher energy density that petroleum diesel and biodiesel. F-T diesel can be used in all existing diesel engines and can be

mixed without a maximum mixture level with petroleum diesel (Wilhelm and others 2001). For instance Audi won the “24 Hours at LeMans” sports car race with F-T diesel. Currently, F-T fuels are produced from syngas originating from natural gas and coal. Biomass syngas can replace fossil fuels as the primary feedstock. 5. Pyrolysis vapors can produce non-energy products Pyrolysis vapors can also be used to produce a number of co-products such as wood preservative, meat browning, food flavorings, adhesives, or specific chemical compounds (Czernik, 2004). Liquid smoke, the chemical used to add smoke flavor to foods, is currently produced by pyrolysis of mesquite and other hardwoods. In local agricultural applications these vapors can be condensed and used as insecticides, herbicides, and fungicides (Steiner, 2007). The bio-oil by product from these processes can be refined as a source of chemical feedstocks to yield products such as acetic acid (vinegar).

6. Biomass pyrolysis can create valuable soil amendments One of the most exciting new benefits of biomass pyrolysis is its ability to produce valuable soil amendments in the form of charcoal (biochar). Biochar is currently used in Japan and in other parts of the world by indigenous tribes. Recent archeological exploration has found that indigenous peoples of the Amazon used charcoal to enrich their soil over 1,000 years ago. This was due to the discovery of a black colored soil in the Amazon basin of Brazil termed Terra Preta. It is believed that prior to the arrival of Europeans, the charcoal in these soils was added by native Amazonians to create arable farmland (Lehmann et al., 2006). Phosphorus (P) and calcium (Ca) are normally scarce in the very acidic Oxisols and Utisols that are predominant in this region. In contrast, Terra Preta soils contain higher levels of P and Ca with a higher, almost neutral pH (Glaser et al., 1998). Another distinctive feature of Terra Preta soil is the high stability of its soil organic matter (SOM), and high cation exchange capacity (Sombroek, 2003), all factors that improve soil fertility.

Figure 2. Co-products from Biomass Pyrolysis (Olglesby, Hawkins, 2007)

The use of charcoal as a soil amendment is not limited to ancient civilizations such as the ones that created Terra Preta. New research has shown that biochar is more efficient at increasing soil fertility and nutrient retention than un-charred organic matter (Lehmann et al., 2006). Carbon enhanced SOM offers direct value through improved water infiltration, water holding capacity, structural stability, cation exchange capacity, soil biological activity and as a CO2 sink (Lehmann, 2007). Charcoal can also reduce fertilizer runoff and adsorb ammonium ions.

The use of biochar has recently been authorized for use as a soil amendment in Japan. Of all of the charcoal used in Japan in 1999, the highest percentage of use was in agricultural land as a soil amendment.

The second highest use was in the livestock industry where it used for animal feed and deodorization (Okimori et al.,2003). In the U.S. a system has been developed where biochar can be amended with ammonium bicarbonate producing a valuable carbon based fertilizer called ECOSS (Day and others, 2005). Other benefits of biochar include its ability to: adsorb soil-damaging pesticides and neutralize natural toxins in decomposing organic materials (Yelverton and others, 1996), and increase soil organic content (Blanco-Canqui et al., 2004). On farm trials in the U.S., a 20% increase in corn yield and a 520% in mycorrhizal populations (beneficial soil fungi that plants depend on) was observed where carbon based soil amendments were applied at 7-9 pounds per acre. In two years of trials at the Virginia Polytechnic Institute, a similar product achieved a 10% increase in sweet corn yield, a 30-pound per acre savings in nitrogen for Irish potatoes and a 47% increase in tomato yield (Morse, R and P. Stevens, 2006,-2008). Observations in the field also verified reduced need for irrigation where carbon based amendments were applied ( http://www.carbonchar.com/). Under proper conditions, scientists have also shown that when added to soil, biochar has the potential to increase soil carbon sequestration by as much as 400%. This is due to its beneficial effects on soil microorganisms, which convert soluble organic matter into stable organic compounds (Day, Reicosky, Nichols 2005). 7. Biomass pyrolysis can be used to sequester atmospheric carbon dioxide Charcoal is commonly used for heating and cooking, and in many developing countries is the only available fuel. In traditional methods of charcoal manufacturing all the valuable chemicals (tars, oils and smoke) and heat escape into the atmosphere. While biomass pyrolysis can provide fuel for heating and cooking, it is vastly different than the smoking kilns and barrels that are currently used throughout the world. Pyrolysis systems that produce biochar and energy do not produce pollution, contaminate water supplies, or create waste disposal problems. To ensure that systems producing biochar are clean and do not contribute to green house gas (GHG) pollution, an organization called the International Biochar Initiative has formed and is setting standards for this product (http://www.biochar-international.org/home.html). Biomass pyrolysis can sequester up to 50% of the initial carbon (C) input and return it to the soil. The initial loss of C can be used for energy production and can offset fuel use (Figure 1.). This contrasts greatly with burning of biomass, which sequesters 3% of the initial C as charcoal, with the rest being emitted to the atmosphere, or biological decomposition which retains only 10 –20% of initial C after 5 – 10 years (Lehmann et al., 2006). Therefore, with its ability to capture and store carbon in the soil, biomass pyrolysis can deliver tradable carbon emission reductions (Lehmann, et.al. 2006). Controlled pyrolysis has recently been approved by the United Nations Framework Convention on Climate Change as a Clean Development Mechanism (CDM) for avoidance of methane production from biomass decay. (http://cdm.unfccc.int/UserManagement/FileStorage/CDMWF_AM_C7UWTIEMRJ05M3D02XWDW80JN989IP).

Figure 3: LETS FIND A NEW PHOTO

In a CDM feasibility study on pyrolysis at an industrial tree plantation, it was calculated that annual processing of 368,000 tons of biomass would provide emissions reductions of 230,000 tons of CO2 per year and could provide jobs for approximately 2,600 people (Okimori, 2003). The latest figures published by the World Bank indicate that the carbon market grew in value to an estimated US$30 billion in 2006 (€23 billion), three times greater than the previous year. As of November 2007, over 850 carbon-offset projects have been registered worldwide with about seven percent of them in the area of biomass fuels (UNEP 2008 Yearbook). One of the first machines for offsetting CO2 emission has been in use in Senegal in the Saint-Louis region since the end of 2007 . In partnership with Areva, the technology was transferred to South Africa to the Necsa Company who has a production license for the southern cone of Africa. The calculation evaluating carbon credits generated by this machine result in: 11.6 tons of CO2-equivalent per ton of green charcoal. Air France, through the intermediary Action Carbone of GoodPlanet, is now giving its passengers the option to compensate their CO2 emissions with carbon credits generated primarily by the Pro-Natura green charcoal project in Senegal. (http://www.pronatura.org/index.php?lang=en&page=greenchar#greenchar2) 7. Carbon from biomass pyrolysis can be used in a wide range of non-soil applications In addition to use for soil applications, biomass carbon can also be considered for more traditional applications. The applications for carbon and its compounds are so widespread that it would be impossible to adequately describe them in a single article. Some common examples include: carbon black as a pigment for printing ink, carbon paper, printer toner, a filler in plastics and rubber, graphite as a lubricant and molding material in glass manufacture, in electrodes for dry batteries, in electroplating, in brushes for electrical motors and as a neutron moderator in nuclear reactors. Activated carbon is used in medicine to absorb toxins, poisons or gases from the digestive system and in air and water purification. Due to the fact the fact that carbon can form alloys with iron, it can also be used in steel production, in chemical reduction, case hardening, and in carbides for cutting and grinding tools. One company that has been evaluating biochar for both soil and conventional use has found that it can become a precursor for a wide range of carbon based products (http://c6scientific.com). Another use for biochar that can achieve carbon emission reduction credits under the Kyoto protocol is its use as a replacement for coal in power generation. Biochar can be used as a direct replacement for coal without the need to modify the existing powerplant. All of the CO2 that is released as a result of replacing fossil fuels with biochar counts toward carbon emission reductions and can be traded in the carbon exchange markets. As pyrolysis systems become more readily available, it is important that system managers take advantage of the full range of applications and markets that may be achieved.

Conclusions Biomass fuels such as wood, herbaceous materials and agricultural by-products currently form the world’s third largest primary energy resource, behind coal and oil. At best, conventional biomass to energy is considered to be carbon neutral. Harvesting biomass to produce energy may not be sustainable because it can result in reduced soil productivity by depletion of carbon and nutrients. Biomass pyrolysis addresses this dilemma, because it can utilize waste products and about half of the original carbon can be returned to the soil (Lehmann, 2007). Utilizing biomass pyrolysis for the production of fuels also has significant advantages when compared to coal fuels because it can eliminate the need for post combustion scrubbing and can reduce nitric oxide (NOx) formation (Bisio et al., 1995). In fact such energy is actually CARBON NEGATIVE, because for each carbon molecule recycled back to the atmosphere, one is buried in the soil, so the net effect is to reduce atmospheric CO2! The deployment of biomass pyrolysis systems can create new local businesses, job opportunities and raise the income of people in rural communities (Okimori et al., 2003). Farming communities can benefit most from this system because the biochar co-product can reduce or eliminate purchased fertilizers while sequestering atmospheric CO2 (Glaser and others., 2002). This can create new profit centers for landowners by creating carbon credits and energy, which farmers can use or sell. This can decentralize fertilizer and energy distribution,

making resources more available to farmers. It can reduce agricultural dependence on petroleum and natural gas based products by allowing regional energy production that is cost competitive with fossil fuels. Although biomass pyrolysis represents only a small portion of energy production worldwide it has the potential to generate energy at a lower cost than other energy systems. With its carbon negative footprint, biomass pyrolysis has the ability to do this in a way that can contribute to reduction in greenhouse gas emissions. Given that 1) soil organic carbon is one of the largest reservoirs in interaction with the atmosphere and 2) enhancing natural processes is thought to be the most cost-effective means of reducing atmospheric CO2; biomass pyrolysis provides a way forward toward overcoming the obstacles that are facing biofuels production today. In the words of USDA Soil Scientist, David Laird, we now have “A Win–Win–Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, while Improving Soil and Water Quality” (Laird, 2008). References (A complete list of the references shown in this paper is available from: http://c6scientific.com). Antal, Michael (1982). Biomass Pyrolysis: A Review of the Literature Part 1- Carbohydrate Pyrolysis. K.W Boer, J.A. Duffie (ed.) Advances in Solar Energy: An annual review of Research and Development Vol 1 American Solar Energy Society, Inc. NY 61-111.

Bisio, Attilio and Sharon Boots (1995) Encyclopedia of Energy Technology and the Environment Vol 3 John Wiley & Sons, Inc, New York, NY 2281-2310.

Blanco-Canqui, H. and Rattan Lal (2004). Mechanisms of carbon sequestration in soil aggregates. Critical Reviews in Plant Sciences 23(6): 481-504.

Czernik, Stefan, Robert Evans, Richard French (2007). Hydrogen from biomass-production by steam reforming of biomass pyrolysis oil. Catalysis Today 129: 265-268.

Czernik, Stefan, A.V. Bridgewater (2004). Overview of Application of Biomass Fast Pyrolysis Oil. Energy Fuels 18: 590-598

Day, Danny, R.J. Evans, J.W. Lee, D. Reicosky (2005). Economical CO2, SOx, and NOx Capture from Fossil-fuel Utilization with Combined Renewable Hydrogen Production and Large-scale Carbon Sequestration. Energy 30: 2558-2579.

Day D, D Reicosky, K Nichols (2005). Internal report to U.S. Office of Management & Budget.

Glaser, Bruno, Ludwig Haumaier, Georg Guggenberger, Wolfgang Zech (1998). Stability of soil organic matter in Terra Preta soils. 16th World Congress of Soil Science, Montpellier, 20-26/08/1998, Proceedings on CD-ROM.

Glaser, Bruno, Johannes Lehmann, Christoph Steiner, Thomas Nehls, Muhammad Yousaf, and Wolfgang Zech (2002). Potential of Pyrolyzed Organic Matter in Soil Amelioration. 12th ISCO Conference: 421-427.

Iwasaki, W. (2003). A Consideration of the Economic Efficiency of Hydrogen Production from Biomass. International Journal of Hydrogen Energy 28: 939-944.

Laird, D.A. (2008) The Charcoal Vision: A Win–Win–Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, while Improving Soil and Water Quality. Agronomy Journal: 100(1) 178-181

Lehmann, Johannes, John Gaunt, Marco Rondon (2006). Bio-Char Sequestration in Terrestrial Ecosystems. Mititagtion and Adaptation Strategies for Global Change 11: 403-427.

Lehmann, Johannes (2007). Bio-energy in the black. Frontiers in Ecology and in the Environment 5: 381–387.

Magrini-Bair, K., S. Czernik, R. French, Y.O. Parent, E. Chornet, D.C. Dayton, C. Feik, R. Bain (2007). Fluidizable reforming catalyst development for conditioning biomass-derived syngas. Applied Catalysis A: General 318: 199-206.

Okimori, Y, Makoto Ogawa, F. Takahashi (2003). Potential of CO2 Emission Reductions by Carbonizing Biomass Waste from Industrial Tree Plantation in South Sumatra, Indonesia. Mitigation and Adaptation Strategies for Global Change 8: 261-280.

Raveendran, K. and Anuradda Ganesh (1996). Heating value of biomass and biomass pyrolysis products. Fuel 75: 1715-1720.

Samolada, M.C., W. Baldauf, and I. A. Vasalos (1998). Production of a bio-gasoline by upgrading biomass flash pyrolysis liquids via hydrogen processing and catalytic cracking. Fuel 77: 1667 – 1675.

Sombroek, W., M L Ruivo, P M Fearnside, B Glaser, and J Lehmann (2003). ‘Amazonian Dark Earths as carbon stores and sinks’, in J. Lehmann, D.C. Kern, B. Glaser and W.I. Woods eds., Amazonian Dark Earths: Origin, Properties, Management, Dordrecht, KluwerAcademic Publishers. 125–139

Steiner, Christoph, K.C. Das, M. Garcia, B Forster, and Wolfgang Zech (2007). Charcoal and smoke extract stimulate the soil microbial community in a highly weathered Xanthic Ferralsol. Pedobiologia In press.

UNDP: (2004). World Energy Assessment; ed. J. Goldemberg and T. B. Johansson, New York, NY, UNDP

UNEP Website: (United Nations Environment Program) (2008) UNEP Launches Year Book 2008 at its 10th Special Session of the Governing Council/Global Ministerial Environment Forum in Monaco (Monaco, 20 February 2008 )

Wilhelm, D.J., D.R. Simbeck, A.D. Karp, R.L. Dickenson (2001). Syngas production for gas-to-liquids applications: technologies, issues and outlook. Fuel Processing Technology 71: 139-148.

Yaman, Serdar (2004). Pyrolysis of biomass to produce fuels and chemical feedstocks. Energy Conversion and Management 45: 651-671.

Yelverton, F.H, Jerome B Weber, G. Peedin, W. D. Smith (1996). Using activated charcoal to inactivate agricultural chemical spills. North Carolina Cooperative Extension Service Pub. AG-442 1-4.

Soil Science and Plant Nutrition (2007) 53, 181–188 doi: 10.1111/j.1747-0765.2007.00123.x

© 2007 Japanese Society of Soil Science and Plant Nutrition

Blackwell Publishing, Ltd.ORIGINAL ARTICLEEffect of charcoal on N2O emissionsORIGINAL ARTICLE

Effects of charcoal addition on N2O emissions from soil resulting from rewetting air-dried soil in short-term laboratory experiments

Yosuke YANAI1, Koki TOYOTA2 and Masanori OKAZAKI2

1Graduate School of Bio-Applications and Systems Engineering and 2Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Tokyo 184-8588, Japan

Abstract

Laboratory experiments were conducted to examine the effect of charcoal addition on N2O emissionsresulting from rewetting of air-dried soil. Rewetting the soil at 73% and 83% of the water-filled pore space(WFPS) caused a N2O emission peak 6 h after the rewetting, and the cumulative N2O emissions throughoutthe 120-h incubation period were 11 ± 1 and 13 ± 1 mg N m−2, respectively. However, rewetting at 64%WFPS did not cause detectable N2O emissions (−0.016 ± 0.082 mg N m−2), suggesting a severe sensitivity tosoil moisture. When the soils were rewetted at 73% and 78% WFPS, the addition of charcoal to soil at10 wt% supressed the N2O emissions by 89% . In contrast, the addition of the ash from the charcoal did notsuppress the N2O emissions from soil rewetted at 73% WFPS. The addition of charcoal also significantlystimulated the N2O emissions from soil rewetted at 83% WFPS compared with the soil without charcoaladdition (P < 0.01). Moreover, the addition of KCl and K2SO4 did not show a clear difference in the N2Oemission pattern, although Cl− and , which were the major anions in the charcoal, had differenteffects on N2O-reducing activity. These results indicate that the suppression of N2O emissions by theaddition of charcoal may not result in stimulation of the N2O-reducing activity in the soil because ofchanges in soil chemical properties.

Key words: denitrification, K fertilization, liming, N2O-reducing activity, rewetting effect.

INTRODUCTION

N2O is an important greenhouse gas produced in soil(Bouwman 1990). It has a destructive potential in thestratospheric ozone layer (Crutzen 1981). Nitrificationand denitrification are the most important biologicalprocesses in the production of N2O in soil. Denitrificationis identically the sole process associated with N2Oreduction (Zumft 1997).

In a previous study, we examined the effects of soilamendments (liming material, inorganic salts andcharcoal) on the N2O-reducing activity of denitrifyingcommunities (Yanai et al.). We found that charcoal andits ash, which had a high content of alkali and inorganicsalts (Nerome et al. 2005), seemed to promote the growthactivity and N2O-reducing activity of denitrifying

communities and that liming and anions affected theseactivities more than cations. These results suggestthat N2O emissions from soil can be affected by certainsoil amendments because of the modifying activity ofN2O reduction, assuming that N2O emissions from soilthrough denitrification depend on the balance of theN2O-producing and N2O-reducing activity of denitrify-ing communities (Cavigelli and Robertson 2001). Infact, Inubushi et al. (1999) and Azam and Müller(2003) observed stimulation of N2O emissions from soilby the addition of NaCl in a laboratory incubationstudy, and this result can be explained by the suppressionof N2O-reducing activity by Cl− or Na+ (Yanai et al.). Incontrast, the effects of liming on N2O emissions fromsoil are inconsistent in field studies (Borken and Brumme1997; Butterbach-Bahl et al. 1997; Klemedtsson et al.1997; Mosier et al. 1998; Tokuda and Hayatsu 2004;Wang et al. 1997) and in laboratory incubation studies(Borken et al. 2000; Clough et al. 2003; Clough et al.2004; Khalil et al. 2003).

Pulses of N2O emission have been observed in fieldstudies following irrigation and precipitation events

SO42−

Correspondence: Y. YANAI, BASE 415, 2-24-16, Nakacho,Koganeishi, Tokyo 184-8588, Japan. Email: [email protected] 31 July 2006. Accepted for publication 15 December 2006.

182 Y. Yanai et al.


(e.g. Kusa et al. 2006; Ruser et al. 2001) and have beenreproduced in laboratory incubation experiments as arewetting of dry soil (Rudaz et al. 1991). Rudaz et al.(1991) and Ruser et al. (2006) investigated the contri-bution of nitrification and denitrification to the produc-tion of N2O emitted after rewetting using the C2H2

addition method and 15N tracing technique, respectively,and concluded that the N2O was mainly producedthrough denitrification. In the present study, to examinethe relationship between enhancing the N2O-reducingactivity of denitrifying communities and N2O emissionsfrom soil, we examined the effects of charcoal andanion species on N2O emissions caused by the rewettingof air-dried soil in the laboratory.

MATERIALS AND METHODS

Soil samples and charcoalThe soil samples examined were the same as those usedin our previous study (Yanai et al.). Soil sampling wasconducted at the Field Museum Tsukui, the FieldScience Center of Tokyo University of Agriculture andTechnology, Tokyo, Japan. Soil samples were collectedfrom a grassland field in which one side was plantedwith Sorghum bicolor (L.) Moench and the other withSorghum sudanense (Piper) on April 2004 and March2005, respectively. The soil is classified as TypicHapludand, and the soil texture is loam to clay loam ata depth of 0–40 cm, with a granular structure (Kurokawa,pers. comm.). After collection, moist soil samples werepassed through a 2-mm mesh sieve, and part of thesample was then air-dried. Selected physico-chemicalproperties of the soil samples are listed in Table 1. Soil

pH (H2O) value was determined in a 1:2.5 air-dried soil(weight) to deionized water (volume) ratio. Total carbonand nitrogen contents of the soils were determinedusing the dry combustion method using a CN CORDERMT-700 (Yanaco, Kyoto, Japan). Water soluble organic Cand -N contents were determined using a TOCmeter (TOC-VCSH, SHIMADZU Co. Ltd., Kyoto, Japan)and an ion chromatograph (LC-20AT, SHIMADZU Co.Ltd., Kyoto, Japan), respectively, in 1:10 extracts (air-driedsoil to deionized water w/v) at 240 rpm for 30 min. Thepopulation density of denitrifiers in the air-dried soilsamples was determined using the most probable numbermethod in five replicates of 10-fold serial dilution (Tiedje1994). Maximum water-holding capacity (MWHC) wasdetermined using the Hilgard method. Particle densitywas determined using the pycnometer method (Blakeand Hartge 1986). Water-filled pore space (WFPS) wascalculated as follows:

WFPS = (Gravimetric water content/ρH2O) · (Bulk density/Porosity)

where Porosity = 1 − (Bulk density/Particle density). In thepresent study, we set the density of water (ρH2O) at 1 g cm−3.

The charcoal, which was made from municipal biowaste,was provided by JFE Holdings. The physico-chemicalproperties of the charcoal are listed in Yanai et al. andits potential usefulness for cultivation was demonstratedby Nerome et al. (2005). Some selected physico-chemicalproperties of the charcoal and its ash, which was obtainedby heating at 700°C for 4 h (as the test of weight loss-on-ignition; LOI), are listed in Table 2. Charcoal and ashpH (H2O) values were determined in a 1:5 air-driedmaterial to deionized water ratio (w/v). The MWHC andparticle density were determined as described above. Anion

Table 1 Selected physico-chemical properties of the air-dried soils examined in this study (oven-dry basis)

Abbreviation of soil name

Date of sampling

pH (H2O)

Total C Total N C/N ratio

WSOC -N Denitrifiers Water

content MWHC Bulk

density Specific gravity Porosity

(mg C g−1) (mg N g−1) (µg g−1) (log MPN g−1) (g H2O g−1) (g cm−3) (cm3 cm−3)

TG2004 Apr. 2004 6.0 69.6 5.62 12.4 155 45.8 6.5 0.15 1.21 0.58 2.05 0.72TG2005 Mar. 2005 5.4 70.3 5.45 12.9 74 6.4 6.2 0.13 1.11 0.59 2.03 0.71

MPN, most probable number; MWHC, maximum water-holding capacity; WSOC, water soluble organic carbon.

NO3−

NO3−

Table 2 Selected physico-chemical properties of charcoal and its ash examined in this study

pH (H2O)†

LOI (%)

Water content

(g H2O g−1)MWHC

(g H2O g−1)

Bulk density (g cm−3)

Particle density (g cm−3)

Anion content (µmol g−1)‡

Cl−

Charcoal 9.3 38 0.14 1.38 0.50 1.64 510 0 9Ash 11.6 – 0.03 – 0.46 – 1240 2 80

†1:5 ratio. ‡Air-dried material basis in Yanai et al. LOI, weight loss-on-ignition; MWHC, maximum water-holding capacity; –, not determined.

NO3− SO4

2−

Effect of charcoal on N2O emissions 183


contents (Cl−, and ) in these materials weredetermined using an ion chromatograph (LC-20AT,SHIMADZU Co. Ltd. Kyoto, Japan) in 1:20 extracts(air-dried material to deionized water w/v) at 240 rpmfor 30 min.

Measurement of N2O emissions from soil after rewettingTo simulate the thin surface layer in arable fields, wherethe soil could be subjected to air-drying followingcontinuous clear weather, 30 g of sieved air-dried soilwas placed in a Petri dish (1.3 cm height and 8.5 cmdiameter) without compaction. As a result, the thicknessof the soil was approximately 0.8 cm. To simulate thecondition of the soil during or immediately after precip-itation, distilled water was added into the soil samplesin the Petri dishes to more than 70% of their MWHC(equivalent to 64% of the water-filled pore space [WFPS]).Immediately after rewetting the soil sample, N2Oemissions were periodically measured using the closed-chamber method (Hutchinson and Mosier 1981). Aclear glass bell-jar (14 cm width, 26 cm height, 2.32 L)was used as a gas-tight chamber to monitor the concen-tration change in the headspace gas. The inlet and outletof the bell-jar were sealed with a rubber stopper and arubber septum, respectively, and the bottom part of thebell-jar was tightly attached with a ground glass-plateusing a high vacuum-sealing compound (HIVAC-G,Shin-Etsu Chemical Co. Ltd., Tokyo, Japan). A pressure-controlling bent (Hutchinson and Mosier 1981) wasinstalled at the rubber stopper in the inlet and gas sampleswere collected through the rubber septum installed at theoutlet. After placing the chamber onto the soil sample,headspace gas was withdrawn five times at 2 or 8 minintervals, depending on the rate of concentration change.N2O concentration in the collected gas sample was analyzedusing a gas chromatograph (GC-14A, SHIMADZU,Kyoto, Japan) equipped with an electron capture detectorand a stainless steel column packed with Porapak-Q (80/100 mesh, 3 mm diameter, 2 m length). The column anddetector temperatures were kept at 90°C and 330°C,respectively. Argon containing 5% CH4 was used as acarrier gas at a flow rate of 23 mL min−1. The N2O emis-sion rate was calculated using the linear regression method(Hutchinson and Mosier 1981). After measurement ofthe N2O emission rate, the chamber was removed and thesoil sample was left at room temperature (approximately20–28°C) without a lid on the Petri dish. The watercontent was maintained during the incubation periodby adding distilled water. N2O emissions were monitoreduntil the first peak of N2O emissions disappeared.

As a preliminary experiment, we examined the effectof moisture content after rewetting on the N2O emissionsfrom soil (TG2005). Distilled water was added into the

soil samples at 17.0, 19.9 and 23.1 mL to adjust therewetted condition to 70, 80 and 91% MWHC, equivalentto 64, 73 and 83% WFPS, respectively. This experimentwas conducted in triplicate.

Effect of soil amendments on N2O emissions from soil resulting from rewettingBased on the result of the preliminary experiment (Fig. 1),the moisture content after rewetting was adjusted tomore than 73% WFPS in this study. First, to simulateprecipitation in grassland amended with charcoal in thesurface layer, 2 mm-sieved charcoal was mixed withsoil (TG2004) in three of six Petri dishes at 10 wt%(equivalent to 13 vol%) before rewetting, and the N2Oemissions were compared with the remaining three Petridishes as the non-added control. The soil samples wereadded with distilled water to moisten the soil of thenon-added control at 78% WFPS. Second, to test whetherthe effect of the charcoal addition on the N2O emissionresults from the stimulation of N2O-reducing activity bypH increase, the charcoal or its ash was mixed with soil(TG2005) in three of nine Petri dishes before rewetting,and three Petri dishes as the non-added control. Theamounts of added charcoal and its ash were determinedin order to set soil pH (H2O) at 6.0, and the rate ofaddition was 8.2 and 1.6 wt%, equivalent to 9.7 and2.0 vol%, respectively. The soil samples were rewettedby adding distilled water, which was necessary to

NO3− SO4

2−

Figure 1 Effect of rewetting on N2O emissions from soil(TG2005). An air-dried soil sample was rewetted usingdistilled water at 64 (×), 73 (�) and 83% (�) of the water-filledpore space (WFPS) and incubated at room temperature. Thevalues shown are the mean ± standard deviation of three replicates.The cumulative N2O emissions during the 120-h incubationperiod at a rewetting level of 64, 73 and 83% WFPS were−0.016 ± 0.082, 11 ± 1 and 13 ± 1 mg N m−2 (equivalent to−0.003 ± 0.03, 2.3 ± 0.3 and 2.8 ± 0.4 µg N g−1soil), respectively.

184 Y. Yanai et al.


moisten the soil of the non-added control at 73% WFPS.Third, to estimate the interaction between the rate ofcharcoal addition and the moisture content after rewet-ting, N2O emissions were compared with three levels ofcharcoal additions (0, 2 and 8.2 wt%, equivalent to 0,2.4 and 9.7 vol%, respectively) in triplicate. Distilledwater was added to the soil samples to moisten the soilof the non-added control (0% charcoal) at 83% WFPS.Finally, as Cl− and were not only the major anionspecies of the charcoal (Table 2), but also were appliedinto arable fields through fertilization, we examined theeffect of anion species of K solution on N2O emissionsafter rewetting. Of the nine Petri dishes containing thesoil samples (TG2005), distilled water, 10 mmol L−1 KCland 5 mmol L−1 K2SO4 solution were each added to threedishes to adjust to 73% WFPS of the soil, and the N2Oemissions were compared. The concentration of K solutionwas decided based on the concentration of K in a commer-cial liquid fertilizer (Otsuka Chemical Co. Ltd., Osaka,Japan), and the estimated load of Cl− and added withthe charcoal, ash and K solution is listed in Table 3.

Calculation of the cumulative N2O emission and statistical analysisThe cumulative N2O emissions were estimated using thelinear trapezoidal method, and the value was expressedas an arithmetic mean and standard deviation (SD). Thelevel of significance of the treatments was examinedusing an unpaired t-test for TG2004 and by anovafollowed by Tukey’s multiple comparison tests forTG2005 (P < 0.05). If one of the mean values of the tri-plicates appeared to lose normality (mean − 2SD < 0),the original data were log-transformed before compari-son (Bland and Peacock 2002).

RESULTS

N2O emissions from soil after rewettingN2O emissions were not detected after rewetting at 64%WFPS, but were detected after rewetting at 73% and

83% WFPS, and the cumulative N2O emissions throughoutthe 120-h incubation period at room temperaturewere −0.016 ± 0.082, 11 ± 1 and 13 ± 1 mg N2O-N m−2

(−0.003 ± 0.03, 2.3 ± 0.3 and 2.8 ± 0.4 µg N2O-N g−1soil),respectively (Fig. 1). Rewetting over 73% WFPS triggeredN2O emissions, but there were no significant differencesin the cumulative N2O emissions between soils rewettedat 73% and 83% WFPS (P = 0.180).

Effects of charcoal addition on N2O emissions after rewetting at 73% WFPS for TG2004The highest N2O emission rate was observed 30 hafter rewetting, and the values were 2620 ± 460 and383 ± 74 µg N m−2 h−1 in the treatments without and withcharcoal addition, respectively (Fig. 2). The addition of

SO42−

SO42−

Table 3 Estimation of Cl− and load onto soil (TG2005) by the addition of charcoal, ash and K solution

Application rate orconcentration

Added into soil(µmol g−1 soil)

Concentration in soil solution (mmol L−1) at

73% WFPS 83% WFPS

Cl– Cl− Cl−

Charcoal 2 wt% 10 0.2 NA NA 10 0.2Charcoal 8.2 wt% 42 0.7 46 0.8 40 0.7Ash 1.6 wt% 20 1.3 23 1.5 NA NAKCl 10 mmol L−1 7.5 0 8.5 0 NA NAK2SO4 5 mmol L−1 0 3.7 0 4.3 NA NA

NA, not applicable with respect to the objectives of this study; WFPS, water-filled pore space.

SO42−

SO42− SO4

2− SO42−

Figure 2 Effect of charcoal addition on N2O emissions fromsoil (TG2004) rewetted at 78% of the water-filled pore spaceof the soil. The values shown are the mean ± standarddeviation of three replicates. The cumulative N2O emis-sions during the 168-h incubation period for the non-addedcontrol and the 10 wt% charcoal addition were 105 ± 14and 11.1 ± 2.4 mg N m−2 (equivalent to 19.9 ± 2.7 and2.1 ± 0.5 µg N g−1 soil), respectively.



charcoal decreased the N2O emission peak by 85% ofthat of the control without charcoal. The cumulativeN2O emissions were 105 ± 14 and 11.1 ± 2.4 mg N m−2

(19.9 ± 2.7 and 2.1 ± 0.5 µg N g−1 soil) in the treatmentswithout and with charcoal addition, respectively. Thecharcoal addition significantly decreased N2O emissionsby 89% of the control value without charcoal (P < 0.01).

Effects of liming (pH 6.0) with charcoal and its ash on N2O emissions after rewetting at 73% WFPS for TG2005The highest N2O emission rate was observed at 12 hafter rewetting in the non-added control and the ash-added soil (Fig. 3), but N2O emissions were kept at alow level in the charcoal-added soil throughout theobservation period (72 h). The cumulative N2Oemissions throughout the 72-h incubation period in thenon-added control, ash-added and charcoal-added soilswere 4.1 ± 1.9, 4.3 ± 1.2 and 0.8 ± 0.7 mg N m−2 (0.9 ± 0.4,1.0 ± 0.3 and 0.2 ± 0.2 µg N g−1 soil), respectively.Charcoal addition decreased N2O emissions by 80% ofthe value of the non-added control (P < 0.05), whereasash addition did not.

Effects of charcoal addition on N2O emissions after rewetting at 83% WFPS for TG2005The N2O emission rate at 6 h after rewetting was lowerin the 2 and 8.2 wt% charcoal added-soils than in the

non-added control, while the N2O emission rate morethan 12 h after the rewetting was higher in the 2 and8.2 wt% charcoal added-soil than in the non-addedcontrol (Fig. 4). The cumulative N2O emissions throughoutthe 72-h incubation period in the non-added control,and in the 2 and 8.2 wt% charcoal-added soil were6.8 ± 0.9, 10.0 ± 0.8 and 10.3 ± 0.6 mg N m−2 (1.5 ± 0.2,2.2 ± 0.2 and 2.4 ± 0.1 µg N g−1soil), respectively. Theaddition of charcoal at 2 and 8.2 wt% significantlyincreased N2O emissions by 47% and 51% of the valuesof the non-added control, respectively (P < 0.01).

Effects of KCl and K2SO4 on N2O emissions after rewetting at 73% WFPS for TG2005The highest N2O emission rate was observed 12 h afterrewetting (Fig. 5). The mean N2O emission rate washigher in 10 mmol L−1 KCl than in 5 mmol L−1 K2SO4

and the non-added control, but considerable variabilitywas observed in the KCl-added soil. The cumulativeN2O emissions throughout the 72 h incubation in thenon-added control, 10 mmol L−1 KCl and 5 mmol L−1

K2SO4 were 2.9 ± 0.6, 5.3 ± 6.1 and 4.4 ± 1.5 mg N m−2

(0.6 ± 0.1, 1.2 ± 1.3, 1.0 ± 0.3 µg N g−1 soil) with CVvalues of 21, 115 and 34% (17, 108 and 30%), respectively.There were no significant differences between thecontrol and the 10 mmol L−1 KCl (P = 0.9986) or 5 mmol L−1

K2SO4 additions (P = 0.8559), or between the 10 mmol L−1

KCl and 5 mmol L−1 K2SO4 additions (P = 0.8794).

Figure 3 Effect of liming by using charcoal and its ash on N2Oemissions from soil (TG2005) rewetted at 73% of its water-filled pore space. The values shown are the mean ± standarddeviation of three replicates. The cumulative N2O emissionsduring the 72-h incubation period for the non-added control,ash-amended soil and charcoal-amended soil were 4.1 ± 1.9,4.3 ± 1.2 and 0.8 ± 0.7 mg N m−2 (equivalent to 0.9 ± 0.4,1.0 ± 0.3 and 0.2 ± 0.2 µg N g−1soil), respectively.

Figure 4 Effect of charcoal addition on N2O emissions fromsoil (TG2005) rewetted at 83% of its water-filled pore space.The values shown are the mean ± standard deviation ofthree replicates. The cumulative N2O emissions during the72-h incubation period for the non-added control and the 2and 8.2 wt% charcoal additions were 6.8 ± 0.9, 10.0 ± 0.8and 10.3 ± 0.6 mg N m−2 (equivalent to 1.5 ± 0.2, 2.2 ± 0.2 and2.4 ± 0.1 µg N g−1soil), respectively.

186 Y. Yanai et al.


DISCUSSION

The present study demonstrated that rewetting ofair-dried soil at 73% WFPS caused significant N2Oemissions (Fig. 1), and the N2O emissions were sup-pressed by the addition of charcoal (Figs 2,3). Thissuppression of the N2O emissions was first consideredto be a liming effect because charcoal has alkali (Table 2)and it had the potential to increase the N2O-reducingactivity of denitrifying communities (Cavigelli andRobertson 2000), which might cause a decrease in N2Oemissions (Cavigelli and Robertson 2001). Therefore,liming resulting from the ash was expected to have asimilar potential for promoting N2O-reducing activityto the charcoal itself. We checked the soil pH (1:2.5ratio) after the observation of N2O emission from soilsto which charcoal and its ash had been added and therewere no significant differences between these amendments(5.7 ± 0.03 and 5.6 ± 0.01, respectively, P = 0.08), butthese treatments were significantly different from thenon-added control (4.9 ± 0.2, P < 0.01, n = 3). However,the addition of ash did not suppress N2O emissions (Fig. 4).Moreover, the suppressive effects of charcoal additionon N2O emissions were not observed when the soilswere rewetted at 83% WFPS (Fig. 4). These resultsindicate that soil pH amendments, which are intended

to stimulate the N2O-reducing activity, may not explainthe suppression of the N2O emissions from soil rewet-ted at 73% WFPS (Figs 2,3). In addition, irrespective ofthe inhibitory effects of Cl− and the stimulatory effectsof on N2O-reducing activity of denitrifying com-munities (Yanai et al.), there were no clear differences inthe N2O emissions when KCl and K2SO4 were addedto the soils (Fig. 5). This finding could result from theuse of concentrations (5 and 10 mmol L−1) that weretoo low to affect the denitrifying communities (Table 3)because the effects of Cl− and were detected at morethan 40 mmol L−1 in the liquid medium in our previousstudy (Yanai et al.). Nevertheless, these results sug-gested that amelioration of the chemical properties ofsoil in order to stimulate the N2O-reducing activity maynot be related to the suppression of the N2O emissionsfrom soil rewetted at 73% WFPS (Figs 2,3).

Increases in N2O emission rates with increasing soilwater contents have been reported from laboratory andfield studies and have been attributed to increasingdenitrifying activity induced by decreased O2 diffusioninto the soil (Ruser et al. 2006 and references therein).In the present study, we observed a similar trend, namely,that N2O emissions increased with increases in the watercontent of soil by rewetting at 73% and 83% WFPS,whereas significant N2O emissions were not detected byrewetting at 64% WFPS (Fig. 1). This result suggests thata decrease in the moisture conditions from 83% to 73%WFPS did not affect the denitrifying communities, whilea decrease from 73% to 64% WFPS may result in a sig-nificant decrease in the anoxic microsites, which resultsin the suppression of denitrification. Thus, undetectableN2O emissions from soil rewetted at 64% WFPS may notbe the result of complete denitrification, including N2Oreduction to N2, but, rather, to insufficient developmentof anoxic microsites in the soil to trigger denitrification.Possibly, this was caused by the soil sample TG2005,which had less denitrification activity because of a lowerpopulation density of denitrifiers, soil pH, and the amountof substrate compared with the soil sample TG2004(Table 1). In addition, the decay of the N2O emission ratein the later incubation period after rewetting may be thecompletion of N2O production (stepwise reductions of

, , and NO) rather than the kinetic equilibra-tion of N2O production and reduction followed by N2

production. Ruser et al. (2006) observed few N2 emissionsafter rewetting, indicating a low or undetectable contri-bution of N2O-reducing activity in the later incubationperiod after rewetting. Therefore, the N2O-reducing activityof denitrifying communities may not significantly affectN2O emissions after rewetting of air-dried soil, suggestingthat the suppressive effect of the charcoal addition onN2O emissions (Figs 2,3) might result from inhibition ofN2O-producing activity of denitrifying communities.

Figure 5 Effect of Cl− and of K salts on N2O emissionsfrom soil (TG2005) rewetted at 73% of its water-filled porespace. An air-dried soil sample was rewetted using distilledwater (control) or a K solution and incubated at roomtemperature. The values shown are the mean ± standarddeviation of three replicates. The cumulative N2O emissionsduring the 72-h incubation period for the non-added control,the 10 mmol L−1 KCl-added soil and the 5 mmol L−1 K2SO4

added soil were 2.9 ± 0.6, 5.3 ± 6.1 and 4.4 ± 1.5 mg N m−2

(equivalent to 0.6 ± 0.1, 1.2 ± 1.3 and 1.0 ± 0.3 µg N g−1 soil),respectively.

SO42−

SO42−

NO3− NO2

−



Although there was no direct evidence to show alinkage between the addition of charcoal and thesuppression of N2O emissions from soil (Figs 2,3), theadded charcoal itself probably absorbed water andimproved the aeration of the soil, leading to a suppressionof N2O production (stepwise reduction of , and NO) similar to the soil rewetted at 64% WFPS (Fig. 1).In fact, the charcoal examined was made up of porousparticles, whereas the ash was nearly pulverized. Suchdifferences in the size and structure possibly affect the waterabsorption capacity of these materials, and may conse-quently cause differences in the soil aeration, the denitrifi-cation process, and N2O emissions from soil, althoughthe charcoal addition did not significantly affect theMWHC or the particle density (data not shown). Hence,the significant increases in N2O emissions by the addi-tion of charcoal to soil rewetted at 83% WFPS (Fig. 4)can be interpreted as an interaction between the insig-nificant improvement of the aeration of the soil and thestimulation of the N2O-producing activity resultingfrom neutralization (e.g. Cavigelli and Robertson 2000).

Charcoal was examined in this study because of itspotential use for soil amendments in temperate regions(Nerome et al. 2005) and in the tropics (Glaser et al. 2002;Yamato et al. 2006). Although any extrapolation of thefindings from this short-term laboratory study to a long-term field scale should be conducted with caution, fieldapplications of charcoal possibly suppress N2O emissionsfrom arable soil, depending on the moisture or aerationconditions of the soil. In contrast, our understanding of theprocess of suppressing N2O emissions from soil by charcoal isstill preliminary. Therefore, further studies are necessary tounderstand both the mechanisms and possible side-effectsof charcoal addition to soil on the suppression of N2Oemissions from soil, such as the activity of assimila-tion, accumulation in soil or NOx emissions from soil.

ACKNOWLEDGMENTS

The authors thank Dr Yuzo Kurokawa (Tokyo Universityof Agriculture and Technology) for providing soil samplesand Mr Sumio Yamada (JFE Holdings) for providing thecharcoal samples. The work described in this report wasfinancially supported by a Sasakawa Scientific ResearchGrant from The Japan Science Society (16-315), the TUA&T21 Century COE program (Evolution and Survival ofTechnology-based Civilization: Professor Masayuki Horio)and by the Japan Society for the Promotion of ScienceResearch Fellowships for Young Scientists (17-6518).

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Cavigelli MA, Robertson GP 2001: Role of denitrifier diversityin rates of nitrous oxide consumption in a terrestrialecosystem. Soil Biol. Biochem., 33, 297–310.

Clough TJ, Kelliher FM, Sherlock RR, Ford CD 2004: Limeand soil moisture effects on nitrous oxide emissions froma urine patch. Soil Sci. Soc. Am. J., 68, 1600–1609.

Clough TJ, Sherlock RR, Kelliher FM 2003: Can limingmitigate N2O fluxes from a urine-amended soil? Aust. J.Soil Res., 41, 439–457.

Crutzen PJ 1981: Atmospheric chemical processes of the oxidesof nitrogen, including nitrous oxide. In Denitrification,Nitrification and Atmospheric Nitrous Oxide. Ed. CCDelwiche, pp. 17–44. John Wiley, New York.

Glaser B, Lehmann J, Zech W 2002: Ameliorating physicaland chemical properties of highly weathered soils in thetropics with charcoal – A review. Biol. Fertil. Soils, 35,219–230.

Hutchinson GL, Mosier AR 1981: Improved soil covermethod for field measurement of nitrous oxide fluxes.Soil Sci. Soc. Am. J., 45, 311–316.

Inubushi K, Barahona MA, Yamakawa K 1999: Effects ofsalts and moisture content on nitrous oxide emission andnitrogen dynamics in Yellow soil and Andosol in modelexperiments. Biol. Fertil. Soils, 29, 401–407.

Khalil MI, Van Cleemput O, Rosenani AB, Fauziah CI,Shamshuddin J 2003: Nitrous oxide formation potentialof various humid tropic soils of Malaysia: A laboratorystudy. Nutr. Cycl. Agroecosys., 66, 13–21.

Klemedtsson L, Klemedtsson AK, Moldan F, Weslien P 1997:Nitrous oxide emission from Swedish forest soils inrelation to liming and simulated increased N-deposition.Biol. Fertil. Soils, 25, 290–295.

Kusa K, Hu R, Sawamoto T, Hatano R 2006: Three years of

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nitrous oxide and nitric oxide emissions from silandicandosols cultivated with maize in Hokkaido, Japan. SoilSci. Plant Nutr., 52, 103–113.

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Ruser R, Flessa H, Russow R, Schmidt G, Buegger F, MunchJC 2006: Emission of N2O, N2 and CO2 from soil ferti-lized with nitrate: Effect of compaction, soil moisture andrewetting. Soil Biol. Biochem., 38, 263–274.

Ruser R, Flessa H, Schilling R, Beese F, Munch JC 2001:Effect of crop type-specific soil management and Nfertilization on N2O emissions from a fine-loamy soil.Nutr. Cycl. Agroecosys., 59, 177–191.

Tiedje JM 1994: Denitrifiers. In Microbiological and

Biochemical Properties. Eds RD Weaver, JS Angle and PSBottomley, pp. 245–267, Soil Science Society of America,Madison.

Tokuda S, Hayatsu M 2004: Nitrous oxide flux from a teafield amended with a large amount of nitrogen fertilizerand soil environmental factors controlling the flux. SoilSci. Plant Nutr., 50, 365–374.

Wang YP, Meyer CP, Galbally IE, Smith CJ 1997: Compari-sons of field measurements of carbon dioxide andnitrous oxide fluxes with model simulations for a legumepasture in southeast Australia. J. Geophys. Res., 102,28 013–28 024.

Yamato M, Okimori Y, Wibowo IF, Anshori S, Ogawa M2006: Effects of the application of charred bark of Acaciamangium on the yield of maize, cowpea and peanut, andsoil chemical properties in South Sumatra, Indonesia. SoilSci. Plant Nutr., 52, 489–495.

Yanai Y, Hatano R, Okazaki M, Toyota K. Chemical factorsaffecting the N2O-reducing activity of denitrifying com-munities – Analysis of the C2H2 inhibition-based N2Oproduction curve of soil.

Zumft WG 1997: Cell biology and molecular basis of denitri-fication. Microbiol. Mol. Biol. Rev., 61, 533–616.

US Offset Market

•  Trends – Fossil fuels will likely be capped – Favor domestic projects over international projects

•  Destroying methane emissions •  Sequestration

–  Forestry –  Soil Management –  Biochar?

Sequestration Projects •  Clean Development Mechanism

– Reforestation/afforestation only – Temporary credits

HFCs, PFCs & N2O reduction

27%

Renewables 35%

CH4 reduction & Cement & Coal mine/bed

20%

Supply-side EE 10%

Fuel switch 7%

Demand-side EE 1%

Afforestation & Reforestation

0.4%

Transport 0.2%

Expected CERs Until 2012 (%) in each category

Outline

•  Theory of offsets •  How offsets could support biochar projects •  Methodology issues •  Current funding from The Climate Trust

$ = CO2 Sequestered x Price • Low Quality US Projects

•  Chicago Climate Exchange: $2-$4/mt CO2

•  High Quality US Projects

•  Voluntary Carbon Standard: $4-$9/mt CO2

•  California Climate Action Registry: $5-$11/mt CO2

•  Mature International Markets

•  EU Emissions Trading Scheme: $10-$40/mt CO2

•  Projections for Early US Market

•  Markey-Waxman Bill : $10-$15/mt CO2

GHG Reduction Reduction Size Qualify for Carbon Finance?

Sequestration Large Yes

Fuel switch Medium Likely to be capped

Less fertilizer fewer soil emissions (N2O and CH4)

Medium/Large Hard to measure

Less fertilizer less fertilizer production

Small/Medium Indirect, hard to measure, likely to be capped

Biochar GHG Reductions

Currently Methodologies

Avoidance of methane production from biomass decay through controlled pyrolysis

•  Small scale •  No credit for carbon sequestration, but… •  Char must be “biologically inert”

•  Volatile C/Fixed C ratio lower than 50%

Next Step: Sequestered Carbon

Carbon Gold methodology for proposed to the Voluntary Carbon Standard

Outline


Unresolved Methodology Issues

•  Recalcitrance •  Guarantee 100 years of permanent sequestration •  Carbon Gold: Volatile C/Fixed C ratio lower than 50%

•  Soil monitoring •  What happens to char that erodes out of the soils?


•  Ownership – Three entities, same reduction 1.  Feedstock owner 2.  Pyrolysis plant 3.  Land owner

•  Carbon Gold: Credits pyrolysis plant •  Sequestered carbon can only be claimed once


•  Environmental impact –  Heavy metals –  Criteria air pollutants –  Microbe health –  Carbon already in soil

Resolved Issue: Waste Feedstocks

•  Leakage – Changes in emissions outside the project

itself •  Direct: Biomass fuel unavailable •  Indirect: displace current farm land for biochar

feedstock plantations land use change •  Carbon Gold: “biomass that would otherwise

have been left to decay or been burned in an uncontrolled manner”

Carbon Markets and Biochar: An Offset Buyers Perspective

North American Biochar Conference August 10th, 2009

Peter Weisberg Offset Project Analyst

[email protected] 503-238-1915

Outline


Source: The McKinsey Quarterly. 2007. “A cost curve for greenhouse gas reductions.”

US Offset Market

•  Trends – Fossil fuels will likely be capped – Favor domestic projects over international projects

•  Destroying methane emissions •  Sequestration

–  Forestry –  Soil Management –  Biochar?

Sequestration Projects •  Clean Development Mechanism

– Reforestation/afforestation only – Temporary credits

HFCs, PFCs & N2O reduction

27%

Renewables 35%

CH4 reduction & Cement & Coal mine/bed

20%

Supply-side EE 10%

Fuel switch 7%

Demand-side EE 1%

Afforestation & Reforestation

0.4%

Transport 0.2%

Expected CERs Until 2012 (%) in each category

Outline


$ = CO2 Sequestered x Price • Low Quality US Projects

•  Chicago Climate Exchange: $2-$4/mt CO2

•  High Quality US Projects

•  Voluntary Carbon Standard: $4-$9/mt CO2

•  California Climate Action Registry: $5-$11/mt CO2

•  Mature International Markets

•  EU Emissions Trading Scheme: $10-$40/mt CO2

•  Projections for Early US Market

•  Markey-Waxman Bill : $10-$15/mt CO2

GHG Reduction Reduction Size Qualify for Carbon Finance?

Sequestration Large Yes

Fuel switch Medium Likely to be capped

Less fertilizer fewer soil emissions (N2O and CH4)

Medium/Large Hard to measure

Less fertilizer less fertilizer production

Small/Medium Indirect, hard to measure, likely to be capped

Biochar GHG Reductions

Currently Methodologies

Avoidance of methane production from biomass decay through controlled pyrolysis

•  Small scale •  No credit for carbon sequestration, but… •  Char must be “biologically inert”

•  Volatile C/Fixed C ratio lower than 50%

Next Step: Sequestered Carbon

Carbon Gold methodology for proposed to the Voluntary Carbon Standard

Outline



•  Recalcitrance •  Guarantee 100 years of permanent sequestration •  Carbon Gold: Volatile C/Fixed C ratio lower than 50%

•  Soil monitoring •  What happens to char that erodes out of the soils?


•  Ownership – Three entities, same reduction 1.  Feedstock owner 2.  Pyrolysis plant 3.  Land owner

•  Carbon Gold: Credits pyrolysis plant •  Sequestered carbon can only be claimed once


•  Environmental impact –  Heavy metals –  Criteria air pollutants –  Microbe health –  Carbon already in soil

Resolved Issue: Waste Feedstocks

•  Leakage – Changes in emissions outside the project

itself •  Direct: Biomass fuel unavailable •  Indirect: displace current farm land for biochar

feedstock plantations land use change •  Carbon Gold: “biomass that would otherwise

have been left to decay or been burned in an uncontrolled manner”

Outline


•  3 Programs •  Oregon Program •  Smart Energy •  Colorado Carbon Fund

•  16 projects, $8.8 million in funding, 2.6 million tons of CO2 offset •  Non-profit

- Laboratory for innovative offset projects

Project Development Timeline

Proposal Due Diligence

Contract Negotiation Commercial

Operation

Annual Monitoring

Upfront Payment

Annual payment “upon delivery”

Peter Weisberg Offset Project Analyst [email protected] 503-238-1915 x 207

www.elsevier.com/locate/chemosphere

Chemosphere 67 (2007) 1033–1042

Differential sorption behaviour of aromatic hydrocarbons oncharcoals prepared at different temperatures from grass and wood

Ludger C. Bornemann a,b,*,1, Rai S. Kookana a, Gerhard Welp b

a CSIRO Land and Water, Adelaide Laboratory, Waite Road, Urrbrae SA, Australiab Institute of Crop Science and Resource Conservation of the University of Bonn, Division of Soil Science, Nussallee 13, 53115 Bonn, Germany

Received 27 June 2006; received in revised form 13 October 2006; accepted 19 October 2006Available online 8 December 2006

In memory of the 100th anniversary of the birth of Prof. Dr. H.C. Eduard Muckenhausen (February 17th 1907)

Abstract

Naturally occurring charcoals are increasingly being recognized as effective sorbents for organic compounds. In this study we inves-tigated the sorption of benzene and toluene in single-sorbate and bi-sorbate systems on different types of charcoals produced in labora-tory, employing the batch sorption technique. Air dried plant materials from Phalaris grass (Phalaris tuberosa) and Red Gum wood(Eucalyptus camadulensis) were combusted under limited oxygen supply at 250 �C, 450 �C, and 850 �C. The resulting charcoals were char-acterized for their specific surface areas, total cation content, and pore size distributions (pore size distribution only for wood combustedat 450 �C and 850 �C). For the materials treated at 850 �C not only the surface area, microporosity, and total amount of sorbed sorbateincreased markedly, but also the non-linearity of the sorption isotherm. The pore size distributions and surface areas as well as an indif-ferent sorption behaviour and competition effects for both sorbates indicated that pore filling mechanisms were the dominating processesgoverning the sorption on these microporous, high temperature treated materials. For the materials treated at lower temperatures theaffinity of toluene was higher compared to that of benzene. In the bi-sorbate system the overall uptake of benzene increased. These phe-nomena might be due to the stronger hydrophobicity of toluene, and to a varying potential for swelling of the matrix and pore defor-mation by the two sorbates. The significantly lower sorption capacity of the Phalaris-derived material compared to the Red Gumcharcoal correlated with its smaller surface area and higher cation content.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Charcoal; Aromatic hydrocarbons; Pore filling; Hydrophobic partitioning

1. Introduction

Charcoal, the solid residue of partially combusted bio-mass, is a major constituent of the non-living organic mat-ter of many soils and sediments (Schmidt and Noack,2000). Together with other species of pyrolytic carbon itcomprises a ubiquitous group of materials in our environ-ment, commonly named black carbon (BC) (Goldberg,1985). Currently, little is known about formation, move-

0045-6535/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.chemosphere.2006.10.052

* Corresponding author. Tel.: +49 228 73 9368; fax: +49 228 73 2782.E-mail address: [email protected] (L.C. Bornemann).

1 PMB 2, Glen Osmond, SA 5064, Australia.

ment, and oxidation of charcoal, but there are indicationsthat frequent vegetation fires and alluvial transport areplaying a major role (Skjemstad et al., 1997). Charcoalwithstands biological and chemical degradation to a con-siderable degree (Goldberg, 1985) and plays an importantrole in the global carbon cycle and carbon sequestrationdue to accumulation processes (Jenkinson, 1990).

Several studies revealed the potential of charcoal toserve as a strong sorbent for environmental pollutants,thereby playing a crucial role in governing their environ-mental fate and risks to human and ecosystem health. Poly-cyclic aromatic hydrocarbons (PAH), polychlorinatedbiphenyls (PCB), and polychlorinated dibenzo-dioxins

mailto:[email protected]

1034 L.C. Bornemann et al. / Chemosphere 67 (2007) 1033–1042

(PCDD) have been detected on carbonaceous geosorbentsand are contaminants of environmental concern (e.g.Accardi-Dey and Gschwend, 2003; Abelmann et al.,2005; Lohmann et al., 2005). However, the majority ofstudies dealing with sorption on activated carbon, soot,coal, charcoal, graphite, opaque particles and other formsof BC has been conducted utilizing rather simple aromaticcompounds as model substances like benzene, toluene, orphenanthrene (e.g. Gustafsson et al., 1997; Kleineidamet al., 2002; Zhu and Pignatello, 2005). The sorption ofthese model substances on BC species has been shown tobe strong and highly non-linear (e.g. Accardi-Dey andGschwend, 2003; Braida et al., 2003; Nguyen et al., 2004;James et al., 2005). Several attempts to explain the sorptionbehaviour of organic materials with varying physicochem-ical properties have been made during the last decade.Chiou et al. (2000) introduced the term of ‘‘high surfacearea carbonaceous material’’ (HSACM). Small amountsof charred material like soot or charcoal are consideredto be responsible for the non-linear sorption of polar andapolar components. The involved mechanisms are assumedto be hydrophobic partitioning and pore filling, accordingto the Polanyi–Manes (PM) model (Manes, 1998). The the-ory postulates the existence of a nonpolar, microporousadsorption site with a characteristic adsorption potential,which is influenced by the nature of the sorbent, and thedistance of the sorption site from the sorbent surface. Alsointeractions of water and adsorbent surface are taken intoaccount. The fundamental idea is a condensation of theadsorbate in (micro-) pores while exhibiting the same phys-ical properties as the unconfined bulk organic liquid orsolid. The sorption capacity is believed to be restricted bythe pore volume occupied by the mixed phase of condensedliquids or solids. Consequently, the sorption of hydropho-bic organic contaminants (HOC) on BC materials would bemainly governed by its microporosity and its hydrophobiccharacter.

The physical properties of charcoals from burned bio-mass are strongly dependent on the conditions during thecombustion process (Shafizadeh, 1984). According toSchmidt and Noack (2000), charcoals produced by vegeta-tion wildfires consist mainly of several randomly orientatedstacks of graphitic sheets. Still, the structure is influencedcrucially by a number of combustion parameters. The mainfactors are the fuel type, fuel load, fuel condition, weathercondition, substrate heterogeneity, fire intensity, and dura-tion (Patterson et al., 1987). Karapanagioti et al. (2004)stated that ‘‘. . .the charcoal particle subgroup of organicmatter is heterogeneous in nature’’, and therefore con-cluded that different subgroups of charcoal have to be dis-tinguished in order to optimize the predictions for the bulksorption behaviour.

So far, little attention has been directed to the heteroge-neity within the subgroup of charcoals. From work of Rai-son (1979) and Scott (1989) we know that elevated groundtemperatures during most wildfires may vary between200 �C and 500 �C, with highest temperatures for scrub-

land wildfires ranging up to levels between 700 �C and1000 �C. Despite these extreme temperature ranges, artifi-cial charcoals as used in most sorption studies consistedeither of charcoals produced from one fixed, or only asmall range of temperatures (Sander and Pignatello,2005; Zhu and Pignatello, 2005; Zhu et al., 2005). A studyby James et al. (2005), however, employed a range of differ-ent combustion temperatures for three species of softwood.Still, the sorptive behaviour of the range of natural char-coals remains poorly understood and data is lacking forcharcoals produced from different parent materials at var-ious temperatures.

The objectives of this study were (i) investigate the sorp-tive properties of charcoals produced from hardwood andherbaceous material at various temperatures representativeof wildfires, and (ii) compare the sorption behaviour of twosimple aromatic model compounds on the range of char-coals in single and bi-sorbate systems.

2. Experimental section

2.1. Wood and grass charcoal production

Red Gum (Eucalyptus camadulensis) chips, as used forgardening purposes, were purchased from a landscape sup-plier, and a pure stand of Phalaris pasture grass (Phalaris

tuberosa) was cut from a meadow. Both materials wereair dried at 40 �C. Thin pieces of Red Gum wood werehand picked, the Phalaris grass was milled into coarse seg-ments and the dust was separated by sieving (2 mm grid).To allow a uniform combustion process, the materials werestacked uncongested in porcelain crucibles with lids. Thefilled crucibles were weighed and subsequently placed in amuffle furnace. For the charcoals combusted at 250 �Cand 450 �C, the furnace was ramped from room tempera-ture to the final temperature in 1 h. As a second stage,the final temperature was held for 2 h for the Red Gumwood. Due to the more combustible nature of the Phalarisgrass, the final temperature was held only for 1 h in thiscase. The furnace was then switched off to allow the cruci-bles to cool down to room temperature. The Red Gumwood treated at 850 �C was combusted for only 1 h afterreaching the final temperature, for the Phalaris grass thetime was reduced to half an hour. The charred materialwas weighed and grinded to powder on a N.V. THEMAdisc-rotating mill for 3 min. In the following, the abbrevia-tions R250, R450, and R850 are used for the Red Gumcharcoals, P250, P450 and P850 for the Phalaris charcoals.

2.2. Determination of charcoal properties

The continuous flow method at 77 K was employed forquantification of adsorbed and desorbed N2, using aQUANTACHROME QUANTASORB QS-13 Surface-Area Particle-Size Analyzer and ultra high purity gaseousnitrogen (99.999%, from BOC Gases). Surface areas forall six utilized charcoals were calculated from three-point

ls �1)

Na

(mg

kg�

1)

K (mg

kg�

1)

Su

m(m

gk

g�1)

Su

mC

Ma

(%)

Su

mD

Mb

(%)

Vm

icro

c

(ml li

qg�

1)

Vto

tald

(ml li

qg�

1)

N2

BE

T-S

SA

e

(m2

g�1)

140

840

611

00.

60.

4–

–8

320

128

08

690

0.9

0.4

0.00

375

0.02

219

3466

02

580

1315

01.

30.

30.

2469

0.27

5760

5

538

017

640

2740

02.

71.

9–

–4

766

029

240

4407

04.

41.

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1266

036

080

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05.

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1938

).

L.C. Bornemann et al. / Chemosphere 67 (2007) 1033–1042 1035

regression, based on the BET equation after Brunauer et al.(1938). Additionally, the pore size distribution of R450 andR850 was evaluated using BET nitrogen adsorption tech-nique at 77 K. The details of the method and uncertaintiesassociated with the measurement have been publishedelsewhere (Badalyan and Pendleton, 2003). Outgassing ofthe charcoal was carried out at 300 �C for 8 h at a back-ground vacuum of 1 · 10�4 Pa, similar to that used forcharcoal samples by Braida et al. (2003). For the pore vol-ume evaluation, we employed aS-plot analysis, where theadsorption properties of a porous solid are compared withthose of a non-porous standard material exhibiting surfacechemistry similar to the test sample (Badalyan and Pendl-eton, 2003). Moisture content was determined by compar-ison of sample mass before and after evacuation at 300 �C.We classified pore width (dp), according to IUPAC recom-mendations as follows: micropores: dp < 2 nm, mesopores:2 < dp < 50 nm, and macropores: dp > 50 nm. Pores, whichwere smaller than 2 nm were analyzed using the Horvath–Kawazoe (H–K) method (Horvath and Kawazoe, 1983).This method calculates the effective micropore size distri-bution of slit-shape pores using the data from adsorptionisotherms. Using the H–K equation we calculated effectivemean width of slit pores (dp), and correlated it with thevalue of DV ads

Drslit, where DVads is the incremental amount of

nitrogen adsorbed (converted to condensed liquid volumeof nitrogen) and Drslit is the corresponding incrementalwidth of slit pores. The individual and cumulative frequen-cies were calculated for a range of dp data. Further infor-mation on the characteristics of these materials hasrecently been published by Smernik et al. (2006) and Yuet al. (2006).

For the measurement of the total cation contents byatomic absorption spectroscopy (AAS), �0.2 g of thecharred material was weighed into microwave vessels and2 ml H2O2 (35%) and 5 ml HNO3 (70%) were added. Thesamples were then digested, using a MILESTONE mls1200 Digestion Unit (300 W, 5 min, 600 W, 5 min, 500 W,3 min). The samples were converted into 50 ml volumetricflasks and made up to volume in Milli-Q water. The liquidwas filtered through 0.45 lm filters and 0.5 ml of the samplewas diluted 20 times prior to AAS analysis. Charcoal prop-erties and composition details are presented in Table 1.

Tab

le1

Sel

ecte

dch

arp

rop

erti

esan

dco

mp

osi

tio

nd

etai

Sam

ple

nam

eC

a(m

gk

g�1)

Mg

(mg

kg

Red

Gu

m25

0�C

485

028

0R

edG

um

450

�C6

700

390

Red

Gu

m85

0�C

940

051

0

Red

Gu

m25

0�C

202

02

360

Red

Gu

m45

0�C

349

03

680

Red

Gu

m85

0�C

474

04

720

aS

um

of

com

bu

sted

mat

ter

(Ch

arco

al).

bS

um

of

dry

mat

ter

(pre

curs

or

mat

eria

l).

cM

icro

po

re-v

olu

me

(<2

nm

).d

To

tal

po

revo

lum

e.e

Sp

ecifi

csu

rfac

ear

eaaf

ter

Bru

nau

eret

al.

(

2.3. Batch sorption

All experiments were conducted in 32 ml KIMAX�

glass culture-tubes (Kimble Glass Inc. USA) with PTFE-lined screw lids to minimize sorption effects on the con-tainer. Aliquots of 32 mg of charcoal were weighed in thereaction vials and hydrated with 20 ml Milli-Q water for42 h in an end-over-end shaker. A pre-hydrating periodof at least 20–24 h is required due to the hydrophobic nat-ure of the charcoal (Zhu and Pignatello, 2005; Zhu et al.,2005). After hydrating, the test sorbate was added as astock solution in a methanol-carrier. Benzene, toluene, pro-


pyl-benzene, methanol, and dichloromethane with HPLC-grade purity (>99.9%) were used in the experiments. Forpractical reasons the sorbate concentrations were preparedas ll l�1and converted into lg l�1 in the calculations. In thesingle-sorbate system, for the materials treated at 250 �Cand 450 �C, the initial sorbate concentrations were cover-ing 2.20–87.90 lg ml�1 for benzene, and 2.17–86.6 lg ml�1

for toluene. Due to the considerably higher sorption capac-ity of the 850 �C materials the concentration range wasexpanded to 351.6 lg ml�1 for benzene and 346.4 lg ml�1

for toluene. In the bi-sorbate systems both sorbates wereadded in equal amounts, the total sorbate concentrationtherefore being doubled, compared to the single-sorbatesystems. In order to prevent varying solvent effects, metha-nol was always kept at 1% by volume throughout allexperiments. Specifications regarding the maximum con-centration of carrier-solvent avoiding interference withthe sorption process are inconsistent (e.g. Kleineidamet al., 2002; Karapanagioti et al., 2004; Sander and Pigna-tello, 2005). However, we found in preliminary experimentsthat keeping the solvent concentration constant at 1% pro-vided reproducible results. To avoid headspace (in order tominimize volatilization losses), the vials were filled up totheir capacity with Milli-Q water. As charcoal in such smallconcentrations suspended in water would hardly settledown during centrifugation, 0.32 ml of 1 M CaCl2-solutionwas added in order to support the flocculation. A final con-centration of 0.01 M CaCl2 was also chosen by otherauthors (Ahmad et al., 2001; Sander and Pignatello,2005). The vials were placed in the end-over-end shakeragain to equilibrate for 24 h. According to Braida et al.(2003), at low initial concentrations (8 lg ml�1), benzenesorption reached an equilibrium after eight days, butthe vast majority of benzene (>95%) was already sorbedwithin 24 h. For higher initial benzene concentrations(�1600 lg ml�1) the apparent equilibrium was shown tobe reached after 24 h. Kwon and Pignatello (2005) reportedthat maximum sorption of benzene on the charcoal alsoutilized by Braida et al. (2003) was achieved within 20 h.From these findings, together with observations that dieselsoot uptake of PAHs occurs within hours to one or twodays (Bucheli and Gustafsson, 2000) we concluded thatequilibration times of 24 h would be appropriate for ourpurposes. The samples were then centrifuged at 650 g fora duration of 10 min. Subsequently, 5 ml of the superna-tant were transferred to PTFE-lined extraction vials with15 ml capacity and extracted with 2 ml dichloromethane.Prior to extraction, propyl-benzene was added as an inter-nal standard. The extraction tubes were then shaken byhand vigorously and an aliquot of the solvent was trans-ferred into PTFE-lined GC-vials. Analysis of the extractswas performed on a PERKIN ELMER Auto System GasChromatograph equipped with a flame ionization detector(FID). The column was a DB-5 column with a length of30 m, an internal diameter of 0.25 mm and a film thicknessof 0.25 lm. The injection temperature was 200 �C with 1 llof sample injected. Helium was used as the carrier gas with

a constant pressure of 22 psi. The detector was heated to250 �C. The initial temperature of the oven was set to35 �C, held for 3 min, and then ramped to 80 �C with a rateof 5 �C min�1.

3. Results

3.1. Charcoal properties

Charcoals combusted at 250 �C and 450 �C exhibitedrelatively low surface areas as revealed by N2-BET surfacearea measurement, whereas the surface areas of the hightemperature treated charcoals (850 �C) were very high(Table 1). The Red Gum charcoals exhibited a much biggersurface area than the Phalaris charcoals at correspondingtemperatures. The ratio of the surface areas of the RedGum charcoals to the ones from Phalaris drops from 2 at250 �C to 1.7 and 1.6 at the higher combustion tempera-tures. For both materials the outstanding increase of thesurface areas (by almost 20 times) occurred between450 �C and 850 �C. This critical change was also docu-mented by the pore size distribution of R450 and R850.The total pore volume of the 850 �C material was higherby more than an order of magnitude than that for the450 �C material (Table 1). Furthermore, the fraction of themicropores (pores <2 nm), vmicro [mlliq g�1], revealed amicroporosity of �90% for the 850 �C material, whereasthe 450 �C material did not exceed a microporosity ofabout 17%. The diagram displaying the integral pore sizedistribution indicated a relatively wide range of porewidths, i.e. 0.5–300 nm, the steep slope at about about1.2 nm pore diameter indicating the large contribution ofthis pore size for the 450 �C material (Fig. 1). On the con-trary, the range of pore size distribution for the 850 �Cmaterial was very narrow (Yu et al., 2006). Here, the over-all dominating pore sizes ranged from only 0.4–1 nm, withinsignificant participation of pores with a diameter >10 nm(Fig. 1). Corresponding to the observed N2-BET surfaceareas, the pore size distribution illustrates the extraordi-nary increase of the inner surface area with decreasingdiameter of the pores.

The total cation content of the Phalaris charcoalsexceeds the one of the Red Gum charcoals by a factorgreater than four (Table 1). Differences in the cation con-tents of grass and wood are also documented in literature.Harmand et al. (2004) found a value of about 0.4% for thesum of calcium, magnesium and potassium in Red Gumwood (Eucalyptus camadulensis) from Cameroon. Consid-ering the low proportion of sodium contributing to thetotal cation content of our Red Gum charcoal (�2–5%),the findings of Harmand et al. (2004) are in line with ourdata (Table 1). For a Phalaris species harvested betweenJuly and October in Sweden, the sum of the four cationsalso determined in our study was reported to be about1.8% of the dry matter (Burval, 1997), and thus again ingood agreement with our data set (Table 1).

0.00

0.10

0.20

0.30

0.1 1.0 10.0 100.0 1000.0d p [nm]

Vto

tal [

ml liq

g -1

] R

850

0.00

0.01

0.02

0.03

Vto

tal [

ml li

qg-1

] R

450

R850

R450

Fig. 1. Integral pore size distribution of the charred material. Total pore volumes (vtotal) of R850 (ordinate on the left) and R450 (ordinate on the right),plotted against the diameter of the pores (dp).


3.2. Influence of the combustion temperature on the

sorption process

Fundamental differences in the sorptive behaviour ofbenzene and toluene were found for the Red Gum materi-als treated at different temperatures. In Fig. 2, we plottedthe sorbed concentration of sorbate q [mg g�1] againstthe final concentration in aqueous solution Cf [mg ml�1]

1

10

100

1000

R250R450R850

a: Benzene

Cf [mg ml-1]

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

q [m

g g-1

]

1

10

100

1000

R250R450R850

b: Toluene

Fig. 2. Sorbed amount of sorbate q plotted against the final sorbateconcentration Cf. Single-sorbate sorption isotherms for (a) benzene and(b) toluene on R250, R450, and R850. Error bars represent standarddeviation of duplicate samples (n = 2). Symbols may cover error bars.

and found Langmuir-type sorption isotherms for R850,after the classification by Giles et al. (1960). Both, benzeneand toluene were sorbed by R850 to a much higher degreethan by the other materials. Comparing the respective coef-ficients of determination (R2) and especially the standarderrors of estimate (SEE), the isotherms from single andbi-sorbate experiments on R850 showed considerably bet-ter fits to the Langmuir than to the Freundlich equation(Table 2). The calculated maximum uptake (Smax) of eachsorbate in the bi-sorbate system was about half of the max-imum uptake in the single-sorbate systems, where benzeneand toluene were sorbed in comparable amounts (Table 2).

Sorption isotherms of R250 and R450 could successfullybe described with the model after Freundlich. For benzene,R250 and R450 exhibited a comparable sorption, whereastoluene expressed a slightly higher affinity to R450 com-pared to R250 (Fig. 2 a and b). In contrast to R850, thesorption of toluene on R450 and R250 was significantlyhigher than that of benzene (Fig. 3 a and b; Table 2).Whereas toluene was hardly affected by competition frombenzene, the benzene uptake even increased in combinationwith toluene on both materials.

3.3. Influence of the precursor material on the sorption

process

The apparent difference between the Phalaris- and RedGum-derived materials was the lower sorption capacityof P850 as compared to R850 (Table 2). For P850, the cal-culated maximum uptake after the Langmuir equationresulted in a value of Smax = 153 mg g�1, whereas the cor-responding value for the Red Gum charcoal was as large as

Table 2Results of model fits to single and bi-sorbate isotherms

Char type Temperature (�C) Single-/bi-solute Sorbate Smaxa (mg g�1) KL

b (ml mg�1) R2c (–) SEE d (–) ne (–) KFf (mln mg1�n g�1) R2g (–) SEE h (–)

Phalaris 850 Single Benzene 153 ± 5.6 245 ± 91 0.99 0.05 0.41 ± 0.05 452.5 ± 1.5 0.86 0.24Redgum 850 Single Benzene 222 ± 3.0 491 ± 99 1.00 0.05 0.45 ± 0.06 981.7 ± 1.7 0.83 0.29Redgum 850 Single Toluene 236 ± 13.4 326 ± 121 0.97 0.03 0.39 ± 0.10 689.6 ± 2.2 0.60 0.38Redgum 850 Bi Benzene 114 ± 8.3 1367 ± 373 0.96 0.01 0.44 ± 0.07 979.0 ± 1.8 0.87 0.22Redgum 850 Bi Toluene 113 ± 1.2 8872 ± 2895 1.00 0.01 0.50 ± 0.18 7206.1 ± 7.7 0.51 0.37Redgum 450 Single Benzene – – – 0.51 ± 0.4 60.9 ± 1.2 0.96 0.07Redgum 450 Single Toluene – – – 0.50 ± 0.01 150.4 ± 1.1 1.00 0.03Redgum 450 Bi Benzene – – – 0.48 ± 0.04 69.2 ± 1.2 0.96 0.07Redgum 450 Bi Toluene – – – 0.47 ± 0.01 126.7 ± 1.1 0.99 0.04Phalaris 250 Single Benzene – – – 0.56 ± 0.03 56.6 ± 1.1 0.98 0.05Redgum 250 Single Benzene – – – 0.55 ± 0.04 63.1 ± 1.2 0.96 0.07Redgum 250 Single Toluene – – – 0.58 ± 0.03 126.3 ± 1.1 0.98 0.05Redgum 250 Bi Benzene – – – 0.56 ± 0.06 83.5 ± 1.3 0.92 0.10Redgum 250 Bi Toluene – – – 0.52 ± 0.04 110.3 ± 1.2 0.95 0.08

Number of observations is 22 for benzene and toluene on materials treated at 850 �C in single sorbate systems, 18 for all other systems.a Maximum sorbate uptake (Langmuir model).b Langmuir affinity coefficient.c Coefficient of determination (Langmuir model).d Standard error of estimate (Langmuir model).e Freundlich exponent.f Freundlich affinity coefficient.g Coefficient of determination (Freundlich model).h Standard error of estimate (Freundlich model).

1038L

.C.

Bo

rnem

an

net

al.

/C

hem

osp

here

67

(2

00

7)

10

33

–1

04

2

Benzene single Toluene singleBenzene bi Toluene bi

C f [mg ml-1]0.0001 0.001 0.01 0.1

q [m

g g-1

]

1

10

1001

10

100a: R250

b: R450

Fig. 3. Sorbed amount of sorbate q plotted against the final sorbateconcentration Cf. Sorption isotherms for (a) single- and bi-sorbate systemsof benzene and toluene on R250, and (b) single- and bi-sorbate systems ofbenzene and toluene on R450. Error bars represent standard deviation ofduplicate samples (n = 2). Symbols may cover error bars (Freundlich-linearization).


Smax = 222 mg g�1. Similar observations were made for the250 �C materials. The Freundlich sorption coefficient (KF)for P250 showed reduced uptake of benzene compared toR250 (Table 2), however, the slopes indicated by the Fre-undlich exponent (n) were similar for both materials.

4. Discussion

4.1. Effect of the combustion temperature on sorption

properties of charcoal

Except for R850, surface areas of laboratory-producedcharcoals in published studies are generally comparablewith our data. The surface area of �600 m2 g�1and amicroporosity of �90% as observed for R850 exceeds themaximum values found in the literature. According to San-der and Pignatello (2005), N2-BET surface areas for typicalcharcoals ranged from 200–500 m2 g�1. However, litera-ture data (Nguyen et al., 2004; James et al., 2005) andour own results suggest that surface areas of charcoalsmay change considerably with varying combustion temper-atures and precursor materials. Surface areas and the porevolumes appear to escalate, and the pore size distributionshifts to a mostly microporous pattern above a critical tem-perature. According to Hellwig (1985), combustion temper-atures of 250 �C are only sufficient to cause the evolution ofvolatiles, whereas at temperatures as high as 450 �C thesoftening of the woody material is already initiated. Resultsof Haghseresht et al. (1999), who examined carbonaceous

adsorbents using 13C NMR, indicated that increased heattreatment results in enhanced contribution of aromaticstructures and an increase of amorphous carbon andmolecular disorder, thereby having impact on amountand size of micropores. Although the amount of microp-ores is still low, the maximum peak for the pore widthsof about 1.1 nm for the material combusted at 450 �C(Fig. 1) is displaying the beginning of micropore formation.

It is noteworthy that despite a significantly higher hydro-phobicity of toluene (benzene: KOW = 134.9; toluene:KOW = 498.8), the calculated maximum uptake (Smax) onR850 was in about the same order of magnitude for bothsorbates in the single-sorbate systems, as well as in the bi-sorbate system. Especially the results of the bi-sorbateexperiments are consistent with the theory of Chiou et al.(2000) and indicate the pore filling mechanism. Accordingto the assumption of an universal adsorbate for the pore fill-ing process, the amount of adsorbed benzene and tolueneshould be about the same when identical volumes of the sor-bates are added. Furthermore, the suppression of thesorbed amount of benzene and toluene from the respectivecompetitor in the bi-sorbate system compared to the single-sorbate system should be about 50% and almost identicalfor both sorbates, since the densities of benzene and tolueneare differing only slightly (benzene: 0.879 g ml�1; toluene:0.866 g ml�1). As seen in Table 2, the calculated maximumuptake for benzene and toluene in the bi-sorbate experimentwas indeed identical for each sorbate and about the half ofthe calculated capacities in the single-sorbate experiments.Considering that in the bi-sorbate system the two sorbateswere added in identical amounts, condensation of the sor-bates in the pores of this highly microporous material(Table 1) could explain the observed phenomenon. This isalso supported by studies of Zhu and Pignatello (2005),addressing pore filling as the most likely dominant processfor the sorption of aromatic compounds on such materials.In their study, the sorptive abilities of a charcoal frommaple wood shavings were compared with that of (non-por-ous) graphite as a model. The experiments displayed sizeexclusion effects on the charcoal for compounds exceedinga certain molecular size, and enhanced sorption on the char-coal compared to the graphite, despite a charcoal graphitepartition coefficient >1. By investigating the effect on poreblocking by lipids on the same material as used by Zhuand Pignatello (2005), Kwon and Pignatello (2005) showedthat benzene sorption is largely located in the interior porework. Still, essential differences are apparent between thematerial used by Zhu and Pignatello (2005) and the char-coals used in our study. The surface area of the maple woodcharcoal (400 m2 g�1) examined by Zhu and Pignatello(2005) was considerably lower than the one of our R850material (605 m2 g�1). Also the microporosity of our mate-rial (�90%, Table 1) exceeds the one of the char from maplewood shavings (�80%). The degree of non-linearity of thesorption process increases with increasing microporosity(after the Polanyi–Manes model), and might thus explainthat the isotherms for our R850 could be described by the


Langmuir model, whereas the isotherms for the maplewood char showed better fit to a Freundlich sorption iso-therm. The sorption on charcoals produced at lower tem-perature in our study also fitted better to Freundlich model.

Kleineidam et al. (2002) investigated the sorption of dif-ferent low-polarity organic compounds on a series of carbo-naceous adsorbents, covering humic soil organic matter,thermally altered carbon materials, and purely engineeredmicroporous sorbents. Employing the PM-model combinedwith linear partitioning for sorbents containing humicmaterial, they were able to predict unique sorption iso-therms by employment of solubility normalized aqueousconcentrations. Their results suggest that the PM-model isthe most appropriate model for sorption processes onhighly porous materials. However, some concerns aboutpotential artefacts resulting from enhanced water adsorp-tion to functional groups of sorbents with varying hydro-philicity have been expressed (Li et al., 2005). Also recentresults by Yang et al. (2006) showed that gaps in the under-standing of the PM-model still exist. Their study revealed,that the molar volume alone (as employed e.g. by Sanderand Pignatello, 2005) in some cases may fail to be an appro-priate scaling factor in order to obtain matching isothermsof hydrophobic compounds with varying molecular sizes.Although the PM-model is increasingly used for modellingof sorption processes, our results among with those of otherresearchers (e.g. Xia and Ball, 2000) show that the classicalapproaches like the Freundlich model and the Langmuirmodel may still be adequate in some cases. These modelsare appropriate here, as the aim of our investigations wasto detect general differences in the sorptive properties ofvarious charcoals, rather than seeking a specific mechanismor an improvement in modelling of sorption isotherms.

The higher sorption of toluene in comparison with ben-zene on R250 and R450 (Fig. 3a and b; Table 2) is possiblydue to its higher hydrophobicity. However, toluene sorptionin single and bi-sorbate system was the same, showing nocompetitive effect. Sander and Pignatello (2005) examinedthe competitive sorption of benzene, toluene, and nitroben-zene on the charcoal mentioned above, which was also uti-lized by Zhu and Pignatello (2005). In their bi-sorbateexperiments, the amount of competitive sorbate was keptconstant while the concentration of the test sorbate chan-ged. From their resulting competitive sorption isotherms itcan be seen that competition effects were most pronouncedwhen the competitor solutes were added at high concentra-tions together with a low concentration of test sorbate.Competition effects diminished as the concentrations ofthe two competing sorbates converged. This explains thelack of significant competition effect from either sorbate inour bi-sorbate systems, as in our experiments both sorbateswere always added in equal concentrations.

In our bi-sorbate experiments, the sorption of benzene onR250 and R450 was even enhanced compared to the single-sorbate system (Fig. 3a and b; Table 2). The reasons for thisare unclear, but may be related to the ability of aromaticcompounds like benzene and toluene to cause the swelling

of charcoal particles. Jonker and Koelmans (2002) foundin their experiments that different solvents exhibited varyingabilities to extract PAHs from soot and sediments and pro-posed a two-step mechanism. According to them, the PAHsare being extracted by an initial swelling of the sorbentmatrix with a subsequent displacement of sorbates by sol-vent molecules. Among a selection of seven popular sol-vents, also comprising two mixtures of benzene and othersolvents, toluene was proven to be the best suited solventfor the extraction of PAHs from charcoal. Therefore, theenhanced sorption of benzene in the bi-sorbate systemsmay result from a toluene-induced swelling of the matrix,thereby opening up additional sorption sites for the smallerbenzene molecules and toluene itself being sterically hin-dered to penetrate by its larger molecular size. Braidaet al. (2003) proved that certain benzene concentrationswere able to induce the swelling of charcoal matrices,thereby increasing the sorption capacity and inducing sorp-tion hysteresis by pore deformation and solvent entrapment.

4.2. Influence of the precursor material on the sorption

process

The lower (�33%) sorption capacity of P850 comparedto R850 (Table 2) is ascribed to the physicochemical differ-ences between the respective materials. Although the expo-sure time to the heat treatment was already reduced due tothe more combustible nature of the grass, the charred grassappeared to be much more disaggregated compared to thewood charcoal. A more extensive combustion, resulting inthe loss of sorption active constituents may have resulted inthe reduced sorption capacity. James et al. (2005) foundthat surface area, pore volume, and microporosity arenot increasing endlessly with increasing combustion tem-peratures, and that softening temperatures are also depen-dent on the precursor material. In their study, a heatingtemperature of 820 �C resulted in drastically reduced sur-face areas and microporosity for a charcoal from Betula

pendula, compared to charcoal produced at a temperatureof 700 �C. For Auraucaria araucana, the softening temper-ature was already reached at 450 �C. Another explanationfor the reduced sorption capacities could be the overallhigher cation content in Phalaris grass compared to RedGum wood (Table 1). As the charcoal was weighed in asbulk, and was not corrected for its content of mineral con-stituents, a higher cation content reduces not only the pro-portion of highly sorptive BC in the bulk, but also increasesthe hydrophilic character of the whole sample. The latter istrue as these cations are present as salts, their hydrophiliccharacter hindering the sorption of hydrophobic compo-nents. Haghseresht et al. (1999) found that the content ofaromatic carbon in the precursor correlated with the con-tribution of amorphous carbon in the corresponding char-coal. A high amount of amorphous carbon results in anincreased abundance of sorption-active edge sites as wellas in an increased disorder, thereby supporting the forma-tion of micropores and increasing the sorption capacity

Table of symbols

Cf final sorbate concentration (mg ml�1)Kd soil water partition coefficient (l kg�1)KF Freundlich affinity coefficient (mln

mg1�n g�1)KL Langmuir affinity coefficientn Freundlich exponentq sorbed amount of sorbate per mass of


(Haghseresht et al., 1999). The content of aromatic carbonin plant tissue is mainly governed by its lignin content. Thelignin content of hardwood (�35%) (Anderson and Till-mann, 1977) is considerably higher than the one forgrasses, with values ranking between �3% and �10% (But-ler and Bailey, 1973). We suggest that also the slightlylower sorption capacity of Phalaris charcoals is likely tobe the combined effect of their smaller surface area, stron-ger hydrophilic effects from mineral salts, and lower lignincontent.

sorbent (mg g�1)Smax maximum sorbate uptake (mg kg�1)

(Langmuir model)SW water solubility (mg l�1)V total volume (ml)vmicro volume of micropores (mlliq g�1)VP vapour pressure (mm HG at 20 �C)vtotal total pore volume (mlliq g�1)dp pore diameter (nm)DVads incremental amount of nitrogen absorbed

(mlliq g�1)Dr incremental width of slit pores (nm)

5. Conclusions

The results from the present studies demonstrated thatcharcoals prepared under different combustion tempera-tures exhibit substantially different physicochemical andthus also sorptive properties, especially if a critical ‘‘soften-ing temperature’’ is exceeded during combustion. For theobserved precursor materials, this critical temperaturewas within the scope of temperatures observed for wildfires(200–1000 �C) (Raison, 1979; Scott, 1989). The charcoalsderived from herbaceous material expressed basically com-parable sorptive patterns to wood charcoals. However,their mineral contents were higher, whereas the N2-surfaceareas and sorption capacities were lower than for the woodcharcoals. The observed highly non-linear sorption behav-iour of R850 and P850 showed better fits to Langmuir iso-therms than to Freundlich isotherms and was most likelyindicative of pore filling processes on the highly micropo-rous charcoal studied here. The surface area varied orderlywith increasing combustion temperature among theobserved charcoals and gave a good indication for thesorptive abilities of the charcoals. Also other parameterssuch as hydrophobicity and swelling of the sorbing matrixseemed to be important for sorption of aromatic hydrocar-bons, as indicated by the enhanced sorption of benzene onR250, R450, and P250 in the presence of toluene. Morework is needed to establish the effect of combustion condi-tions on the nature of charcoals and their subsequentimpact on sorption and desorption behaviour of organiccontaminants.

Acknowledgements

The measurement of pore size distributions was con-ducted by Dr. Alexander Badalyan (University of SouthAustralia), N2 BET-SSA and total cation contents weredetermined by Mr Lester Smith (CSIRO Australia). MsNatasha Waller (CSIRO) provided valuable technical assis-tance during these studies. The authors would like to thankDr. Sonja Brodowski (University of Bonn) and Dr. G.-G.Ying (CSIRO) for their comments on the manuscript. Lud-ger Bornemann was partially funded by the ‘‘Studienstif-tung des deutschen Volkes’’ while working on this projectat CSIRO laboratories in Adelaide.

Appendix A

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Sorption and Desorption Behaviors of Diuron in Soils Amendedwith Charcoal

XIANG-YANG YU,†,‡ GUANG-GUO YING,†,§ AND RAI S. KOOKANA* ,†

CSIRO Land and Water, Adelaide Laboratory, PMB 2, Glen Osmond 5064, South Australia,Australia; Food Safety Research Institute, Jiangsu Academy of Agricultural Sciences,

Nanjing 210014, China; and Guangzhou Institute of Geochemistry, Chinese Academy of Sciences,Guangzhou 510640, China

Charcoal derived from the partial combustion of vegetation is ubiquitous in soils and sediments andcan potentially sequester organic contaminants. To examine the role of charcoal in the sorption anddesorption behaviors of diuron pesticide in soil, synthetic charcoals were produced throughcarbonization of red gum (Eucalyptus spp.) wood chips at 450 and 850 °C (referred to as charcoalsBC450 and BC850, respectively, in this paper). Pore size distribution analyses revealed that BC850contained mainly micropores (pores ≈ 0.49 nm mean width), whereas BC450 was essentially not amicroporous material. Short-term equilibration (<24 h) tests were conducted to measure sorptionand desorption of diuron in a soil amended with various amounts of charcoals of both types. Thesorption coefficients, isotherm nonlinearity, and apparent sorption-desorption hysteresis markedlyincreased with increasing content of charcoal in the soil, more prominently in the case of BC850,presumably due to the presence of micropores and its relatively higher specific surface area. Thedegree of apparent sorption-desorption hystersis (hysteresis index) showed a good correlation withthe micropore volume of the charcoal-amended soils. This study indicates that the presence of smallamounts of charcoal produced at high temperatures (e.g., interior of wood logs during a fire) in soilcan have a marked effect on the release behavior of organic compounds. Mechanisms of this apparenthysteretic behavior need to be further investigated.

KEYWORDS: Diuron; sorption; desorption; soil; charcoal; carbonization; hysteresis

INTRODUCTION

Black carbon (e.g., soot and charcoal) produced from theincomplete combustion of vegetation and fossil fuel is ubiquitousin terrestrial and aquatic environments (1, 2). In addition todispersal through biomass and fossil fuel combustion in theenvironment, some agricultural practices may also contributeto the increasing amount of black carbon in agricultural soils.For example, it is an old practice in the eastern and southernparts of China to mix firewood ashes with soils and livestockdung followed by heating and aging for several months, beforethe mixture is added directly into the field as a fertilizer. Directburning of plant residues in the field after harvest for landclearing is common all over the world. Such agriculturalpractices will also provide direct input of black carbon intoagricultural soil (3-6). Terrestrial black carbon, being erosion-prone, is readily transported by wind and water and is oftendeposited into aquatic ecosystems. Black carbon has been foundto make a significant proportion of soils and sediments: 15-

30% of total organic matter in marine sediments (7) and 12-31% of deep-sea sediments (8), 18-41% of the soils andsediments collected from the suburban area of Guangzhou,China (9), up to 30% of soils collected around Australia (4,10), and up to 45% of total organic carbon (TOC) in soilscollected from Germany (11).

It has been well recognized that the presence of charcoal insoil could not only enhance the sorption of organic contaminantssuch as pesticides (12) but also influence the nature of thesorption mechanism (13). Research in recent years (14) hasshown that the residues produced from burning wheat and ricewere 400-2500 times more effective than soil in sorbing diuronover the concentration range of 0-6 mg/L in water. However,the effect of these amendments on the desorption behavior ofdiuron was not investigated in that study.

The nature and properties of black carbon are stronglyaffected by the nature of parent materials (wood, grass) andthe temperature experienced during combustion (2, 15). Char-coals formed from lignocellulosic materials under conditionsof pyrolysis become increasingly carbonized as temperaturesrise above 500°C and are completely carbonized as temperaturesapproach 1000°C (15). Under relatively high pyrolysis tem-peratures (500-700 °C), the charcoal derived from wheat was

* Corresponding author (e-mail [email protected]; fax+61 883038565).

† CSIRO Land and Water.‡ Jiangsu Academy of Agricultural Sciences.§ Chinese Academy of Sciences.

J. Agric. Food Chem. 2006, 54, 8545−8550 8545

10.1021/jf061354y CCC: $33.50 © 2006 American Chemical SocietyPublished on Web 10/11/2006

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found to be well carbonized and had a relatively high surfacearea and low oxygen content (16). Such chars have been reportedto show high affinity for organic compounds (16, 17), especiallyfor polar solutes (16).

Despite the fact that the environmental fate and impact ofcontaminants (bioaccessibility, bioavailability, and toxicologicalimpact) are strongly influenced by their desorption behavior(18-21), the effect of black carbon on the desorption behaviorof compounds has so far received limited attention. Braida etal. (22) observed pronounced hysteresis in the sorption ofbenzene in water to pure-form maple-wood charcoal preparedby oxygen-limited pyrolysis. Here they found that the sorptionof wood charcoal was highly irreversible and proposed thathysteresis was due to pore deformation of charcoal duringdesorption of the sorbate, leading to entrapment of moleculesas the polyaromatic scaffolding collapsed during desorption.

The objective of this study was to assess the effect of thepresence of small amounts of charcoal materials (prepared fromeucalyptus wood at two different temperatures of 450 and850 °C) in soil on the sorption-desorption behaviors of pesti-cides in soil. Sorption and desorption behaviors were investi-gated to assess the role of the types and amounts of charcoal assorbent for pesticides (represented by diuron as a model nonionicpesticide) in soils amended with various amounts of charcoals.

EXPERIMENTAL PROCEDURES

Chemicals.Diuron [N-(3,4-dichlorophenyl)-N,N-dimethyl urea, withpurity >99%] was obtained from Sigma-Aldrich (Sydney, Australia).Diuron is a nonionic urea herbicide with a very wide use globally.The herbicide is nonvolatile (vapor pressure is 1.1× 10-3 mPa at25 °C), has a water solubility of 36.4 mg/L, and is stable in neutralmedia. Its reported average soil half-life is in the range of 90-180days (23). Sodium azide was obtained from Fluka (Sydney, Australia).Calcium chloride of analytical grade and all solvents of HPLC gradewere obtained from Merck Pty. Ltd. (Victoria, Australia). A stocksolution of 100 mg/L of diuron was prepared in methanol.

Charcoal, Soil, and Sorbent.Charcoals were prepared from redgum wood (Eucalyptusspp.), at two different temperatures, namely,450 and 850°C (BC450 and BC850, respectively). Red gum woodchipswere air-dried at 40°C, and pieces of<5 mm were hand picked forthe carbonization process. The woodchips were placed in porcelaincrucibles with lids in a temperature-programmable muffle furnace(S.E.M., Australia). The temperature of the furnace was ramped to thedefined temperature (450 or 850°C) and held for 2 h for BC450 andfor only 1 h for BC850. The prepared black carbon materials wereground to a fine powder on a disk-rotating mill for 3 min.

The specific surface areas (SSA) of the two charcoals were evaluatedusing the Brunauer, Emmett, and Teller (BET) nitrogen adsorption tech-nique (24) at 77 K, using an automated manometric gas adsorptionapparatus (25) and ultrahigh-purity gaseous nitrogen (99.999%, fromBOC Gases). The details of the method and uncertainties associatedwith the measurement have been published elsewhere (25). Outgassingof the charcoal was carried out at 300°C for 8 h at abackgroundvacuum of 1× 10-4 Pa, similar to that used for charcoal samples byBraida et al. (22). For the pore volume evaluation, we employedRS-plot analysis, where the adsorption properties of a porous solid arecompared with those of a nonporous standard material exhibiting surfacechemistry similar to that of the test sample (25). Moisture content wasdetermined by comparison of sample mass before and after evacuationat 300°C.

We classified pore width (dp) according to the International Unionof Pure and Applied Chemistry (IUPAC) recommendations as fol-lows: micropores,dp < 2 nm; mesopores, 2< dp < 50 nm; and macro-pores,dp > 50 nm. Pores smaller than 2 nm were analyzed using theHorvath-Kawazoe (H-K) method (26). This method calculates theeffective micropore size distribution of slit-shape pores using the datafrom adsorption isotherms. Using the H-K equation we calculated theeffective mean width of slit pores (dp) and correlated it with the

value of∆Vads/∆rslit, where∆Vadsis the incremental amount of nitrogenadsorbed (converted to condensed liquid volume of nitrogen) and∆rslit

is the corresponding incremental width of slit pores. The individualand cumulative frequencies were calculated for a range ofdp data. Otherproperties of these chars as characterized using NMR techniques havebeen published elsewhere (27).

The soil used in this experiment was collected from the RoseworthyCampus, University of Adelaide, and was amended with charcoal. Afterair-drying, the soil was passed through a 2 mmsieve. This soil contained87.8% sand, 1.3% silt, 8.3% clay, and 1.4% organic matter and is ofsandy loam texture. The soil pH value was 6.8 in a 1:5 (soil/water)soil suspension and had a maximum water-holding capacity of 34.2%(v/v) and a cation exchange capacity of 9.3 cmol(+)/kg. The soil wassterilized by autoclaving at 120°C under 300 kPa chamber pressurefor 30 min three times within 3 days.

Charcoal-amended soils used in the experiment were prepared bymixing the above soil and the two types of charcoal at different ratios.The percentages of charcoal materials in the amended soils were 0,0.1, 0.5, 1.0, 2.0, and 5.0% (w/w) for BC450 and 0, 0.1, 0.2, 0.5, 0.8,and 1.0% (w/w) for BC850. The charcoal-amended soils were thor-oughly mixed on a rotary shaker for 7 days before their use as sorbentsfor sorption and desorption experiments.

Sorption and Desorption Isotherms. Diuron sorption by thesorbents was measured by the batch equilibration technique. Preliminarykinetic experiments showed sorption and desorption of diuron incharcoal-amended soils reached an apparent equilibrium within 24 h.Although sorption is known to continue for days at a very slow rate,for the comparative assessment between different chars under similarconditions, the 24 h shaking time was deemed to be adequate for thepurposes of this study. The sorbents were suspended in 10 mL of 0.01M CaCl2 solutions (containing 0.5% NaN3 to inhibit microbial activity)spiked at concentrations from 1 to 27 mg/L of diuron. The amounts ofcharcoal-amended soil used in the experiments were adjusted to allowfor 30-80% of the added chemical to be sorbed at equilibrium. Onthe basis of our preliminary experiments, for BC450-amended soil analiquot of 1.0 g of soil was used for 0, 0.1, 0.5, 1.0, and 2.0% and only0.2 g of soil for 5.0%. For BC850-amended soils, an aliquot of 0.5 gof soil was used for 0.1 and 0.2% and only 0.2 g for 0.5, 0.8, and1.0% amendment. The suspensions were shaken on a rotary shaker atroom temperature (22( 2 °C) at 120 rpm for 24 h and then centrifugedat 4000 rpm for 60 min. After centrifugation, an aliquot of the super-natant in each tube was taken out and analyzed directly by high-performance liquid chromatography (HPLC).

Each sorption test was carried out in triplicate. Losses during thetest were monitored by including two blank controls in each test: onetube that had only a chemical solution without any sorbent and theother control tube that had only the sorbent and CaCl2 solution withoutchemical. Tests showed losses due to adsorption to glassware anddegradation were negligible, and no interferences were found duringthe analysis of solutions. This is consistent with previous studies andthe nature of the chemical (persistent and nonvolatile).

Desorption experiments were conducted for those samples with thehighest sorption loading. After 24 h of equilibration, the tubes werecentrifuged and 5 mL of the supernatant in each tube was taken outfor analysis. Another 5 mL of 0.01 M CaCl2 (including 0.5% NaN3)was added into each tube, and the tubes were shaken for 24 h again.The desorption process was repeated three more times for each tube.All tests were performed in triplicate.

Pesticide Analysis.Analysis of diuron in the supernatant fractionfrom sorption and desorption experiments was carried out on an Agilent1100 series high-performance liquid chromatograph (HPLC) fitted witha diode array detector and an SGE C18 RS column (250× 4.6 mm,5 µm). Acetonitrile (ACN) and water were used as the mobile phase,which was programmed from 36% ACN at 0 min to 80% ACN at 6 minat a flow rate of 1 mL/min. The UV wavelength for detection of diuronwas 248 nm. The detection limit for diuron was 0.03 mg/L.

Data Analysis. The sorption and desorption isotherms were fittedwith the linear form of the Freundlich equation

log Cs ) log Kf + N log Cw

8546 J. Agric. Food Chem., Vol. 54, No. 22, 2006 Yu et al.

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whereCw is the concentration of the chemical in solution,Cs is theconcentration of the chemical in the sorbent,Kf is the Freundlichsorption coefficient, andN is the exponent indicative of sorptionmechanism. The sorption-desorption apparent hysteresis index (H) wasdetermined by the equation (28)

where N and Nd are the Freundlich exponents calculated from thesorption and desorption isotherms, respectively.


Characteristics of Charcoals.Upon carbonization at 450and 850°C, 100 g of red gum chips produced about 36.1 and28.8 g of charred materials, respectively. These are relativelyhigher yields of charcoal than those derived from burning cropresidues (29). The color was gray to black for the BC850,whereas for BC450 it was a little brown to black. The relativelylower mass that remained under higher burning temperatureindicates that BC850 is carbonized to a greater degree thanBC450. The higher mass recovery of red gum chip-derivedcharcoal is believed to be due to the more condensed structureof wood chips than that of crop residues.

For the charcoal BC450, the shape of the nitrogen adsorptionisotherm was similar to that for nonporous materials (Figure1A), suggesting a negligibly small micropore volume (30). Incontrast, the BC850 is a microporous material with a highspecific surface area. The initial steep portion of the adsorptionisotherm for BC850 is indicative of the presence of microporesin the charcoal material (30).

The SSA for BC850 was much higher than that of charcoalBC450 (Table 1) and also higher than wheat-residue-derivedchars, the highest SSA of which was reported to be 438 m2/g(charred at 600°C) (16). Chun et al. (16) also found char surfacearea to increase with increasing charring temperatures (300-600 °C); however, SSA measurement of char produced at700°C was lower than that of char produced at 600°C, whichthey speculated to be due to microporous structures which weredestroyed at 700°C.

Charcoal BC450 has a very low level of microporosity (peakmaxima occurred at a pore width of about 1.1 nm) (Figure 2).This may indicate the beginning of micropore formation at450 °C. Increasing the preparation temperature, as in the caseof charcoal BC850, clearly promoted the formation of micro-pores with the maximum peak occurring for pore widths of about0.49 nm and essentially all pores<1 nm in pore width.

From the pore volume values listed inTable 1, we regardcharcoal BC450 as a non-microporous material. Therefore, thelower temperature (450°C) used for the preparation of charcoalmaterials did not lead to the formation of microporous structure.In contrast, charcoal BC850 is predominantly a microporousmaterial with about 89.6% of volume from micropores (in termsof specific micropore volume). It is customary to express thetotal specific pore volume (V total

pore) of an adsorbent as the liquidvolume adsorbed at a certain value of relative pressure (P/P0

) 0.95) (31). The gaseous nitrogen volume adsorbed at thisvalue of relative pressure was converted into a liquid volumeof nitrogen. For mixed-pore materials, the mesopore volume isdetermined as the difference between the total specific porevolume and total specific micropore volume.

Sorption-Desorption Isotherms and Their Nonlinearity.The presence of charcoal in the soil caused the sorption iso-therms to change progressively into highly nonlinear, concave-downward-shaped isotherms (Figures 3and4). Most of the dataon sorption and desorption isotherms fitted well to the Freund-

lich equation (Table 2); however, at the highest level of charcoalamendment, the fit was noted to be relatively poor in both typesof chars. Instead, the data showed a much better fit to theLangmuir model in these cases. The increasing Freundlichsorption coefficientKf values and decreasingN values withcharcoal content in soil (Table 2) show that the sorption capacityof diuron on charcoal-amended soils gradually increased withincreasing content of charcoal in soil. TheN values decreasedfrom 0.83 to 0.25 and 0.16, respectively, for BC450 and BC850,

Figure 1. Nitrogen adsorption/desorption isotherm for (A) BC450 and(B) BC850.

Table 1. Characteristics of Black Carbon Materialsa

BCburningtemp(°C) abbrev

SSA(m2/g)

moisturecontent

(%)V total

micro

[mL (liq)/g]V total

pore

[mL (liq)/g]

450 BC450 27.330.035 11.7 0.00374 ± 0.00004 0.02219 ± 0.00004850 BC850 566.390.31 9.9 0.2469 ± 0.0039 0.2757 ± 0.0015

a V totalmicro ) volume of total specific microspore; V total

pore ) volume of specificmicrospore and total specific pore.

H ) N/Nd

Sorption/Desorption of Diuron in Charcoal-Amended Soils J. Agric. Food Chem., Vol. 54, No. 22, 2006 8547

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as the amount of charcoal in soil increased from 0.1 to 5.0% ofBC450 and to 1.0% of BC850 (Table 2).

Highly nonlinear sorption isotherms and high sorption capac-ity for organic compounds on sorbents (e.g., soils and sediments)containing black carbon have been observed in a number ofstudies (e.g., refs32-35). Soil organic carbon has commonlybeen hypothesized to consist of an amorphous phase and acondensed phase of organic carbon (36, 37), which are consid-ered to be responsible for partitioning and sorption, respectively.Depending upon the relative contents of the two phases oforganic carbon, sorption by soils and sediments could rangefrom linear partitioning to highly nonlinear sorption (34, 38,39).

Due to the highly nonlinear nature of isotherms, a comparisonof sorption affinities among the charcoal-amended soils needsto be calculated for a specific solution concentration [e.g.,Cw

of 1 mg/L, whereKf ) Kd(Cs/Cw)]. On this basis the sorptioncapacities of the charcoal amended soil were 7-80 times forBC450 and 5-125 times for BC850 in comparison to that ofcharcoal-free soil (Table 2). The sorption contribution of evensmall additions of charcoals to the soil (0.5% of BC450 and0.1% of BC850) was very high indeed (>85%), assuming nochange in inherent sorption capacity of soil. This shows thatthe presence of even small amounts of highly carbonaceousblack carbon (charcoal, soot, or other carbonaceous materials)can dominate sorption of an organic compound in soils andsediments.

Desorption Behavior and the Role of Microporosity.Sorp-tion and desorption isotherms were compared to assess the

Figure 2. Pore size distribution for (A) BC450 and (B) BC850. Using theHorvath−Kawazoe (H−K) method (26), we calculated the effective meanwidth of slit pores, dp, and plotted against the value of ∆Vads/∆rslit, where∆Vads is the incremental amount of nitrogen adsorbed (converted tocondensed liquid volume) and ∆rslit is the corresponding incremental widthof slit pores.

Figure 3. Influence of BC450 on sorption and desorption of diuron insoil. (Inset) Sorption−desorption on unamended soil and on 0.1% BC450.

Figure 4. Influence of BC850 on sorption and desorption of diuron insoil. (Inset) Sorption−desorption on unamended soil and on 0.1% BC850.

Table 2. Freundlich Constants for the Sorption (Kf, N) and Desorption(Kfd, Nd) of Diuron on Soil Amended with Charcoal and the CalculatedHysteresis Index (H)

charcoal

content ofcharcoal in

soil (%) Kf N R 2 Kfd Nd R 2 H

original soil 4.08 0.83 0.9974 5.40 0.73 0.9975 1.14

BC450 0.1 4.47 0.82 0.9994 11.1 0.48 0.9944 1.690.5 28.0 0.45 0.9983 47.5 0.23 0.9990 1.931.0 514 0.37 0.9979 78.6 0.21 0.9977 1.792.0 109 0.34 0.9958 168 0.12 0.9772 2.875.0 314 0.25 0.9980 427 0.10 0.8784 2.37

BC850 0.1 25.3 0.37 0.9979 39.5 0.28 0.9958 1.320.2 72.8 0.32 0.9911 138 0.09 0.9926 3.540.5 224 0.22 0.9875 371 0.04 0.9990 5.140.8 350 0.21 0.9928 576 0.02 0.9004 9.751.0 500 0.16 0.9249 727 0.01 0.8194 14.92


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degree of reversibility of sorption reaction. Due to the shortequilibration time (24 h) employed here, it is not appropriateto refer to the discrepancy between the sorption and desorptionflanks of the isotherms as true hysteresis. This is because thesorption kinetics may have been slow and the sorption reactionmay have continued beyond the point in time when the desorp-tion part of experiment was initiated. Nevertheless, a comparisonof these isotherms does provide an assessment of the impact ofthe nature of sorbate on the desorption behavior of diuron orlack of it. For the purposes of this study, by hysteresis we mean“apparent hysteresis”.

The highly nonlinear sorption isotherm and relatively flatdesorption isotherm inFigures 3and4 provide visual evidenceof apparent sorption-desorption hysteresis on the charcoal-amended soils. We calculated the hysteresis index (H), definedas theN/Nd ratio (28), to quantify the degree of apparent hys-teresis. TheH values for all of the sorbents are listed inTable2. For the original soil sample theH value was 1.14, indicatingminimal desorption hysteresis. As the content of charcoal inthe soil increased, the value ofH also increased. For the soilsamended with charcoal BC850, theH values increased rapidlyfrom 1.32 for the soil with 0.1% of charcoal to 14.92 for 1.0%of charcoal. For the soils amended with charcoal BC450 theH value also progressively increased but at a slower rate. Theresults showed that besides the high sorption capacity, charcoalproduced under higher temperature either had stronger sorptionor provided domains for diffusion of sorbate into micropores.In this way the more microporous structure may lead to effectivesequestration of a compound. This is consistent with the studiesreporting poor bioavailability and bioaccessibility of organiccompounds sorbed on black carbon materials (40, 41).

Comparison of the results for the two types of charcoalmaterials also revealed that although the sorption capacity of asoil could be enhanced to the same level by adding differentialamounts of chars (0.8% BC850 vs 5% BC450), the degree ofreversibility was quite different between the two charcoals. Inthe present study, the discrepancy between sorption and de-sorption isotherms at comparable levels of sorption (e.g., 0.8%BC850 vs 5% BC450,Table 2) was clearly much moreprominent in the case of charcoal BC850.

To assess if a link between the microporosity and apparentdesorption hysteresis exists, we plotted the values of the totalpore volume for each sorbent calculated from theV total

pore valueand the content of charcoal material in the soil against theapparent hysteresis index (H) in Figure 5. Here, we assumedthat the soil free of charcoal is a nonporous material and thatthe pore volume of the charcoal-amended soils was mainlyprovided by the added charcoal.Figure 5 shows a good rela-tionship between these two parameters; theH index increasedexponentially (y ) 1.582 e0.008x, R2 ) 0.8982) as the total porevolume of the sorbent increased. A smaller increase inH valueat lower pore volume is essentially associated with the presenceof charcoal BC450 and only small amounts of BC850. This isbecause charcoal BC450 had a negligible proportion of micro-pores, whereas in BC850 essentially all pores existed as micro-pores of<1 nm width. These micropores either entrapoed thesorbed molecules of diuron or caused a slow and prolongedsorption phase, which may have led to the apparent hysteresisdue to nonequilibrium processes. Braida et al. (22) noted swell-ing of a sorbent during benzene sorption and suggested poredeformation during desorption causing desorption hysteresis.It has also been suggested in other studies that surface-specificadsorption, entrapment into micropores, and partitioning into

condensed structures of soil organic matter are among the maincauses of chemical sequestration (35-37, 42-45).

Conclusions.This study showed that the presence of smallamounts of black carbon in the form of charcoals in soil,especially those produced at high temperatures (e.g., interiorof wood logs during a fire), can have a major effect on thesorption and desorption behaviors of organic compounds suchas the diuron pesticide. The marked effect on the desorption ofhighly carbonaceous materials such as charcoal produced at hightemperatures is expected to have strong implications for thebioavailability of such compounds in terrestrial and aquaticecosystems. The role of such carbonaceous materials onsorption-desorption kinetics and bioavailability needs to befurther investigated.

ACKNOWLEDGMENT

We acknowledge the contributions by Drs. Phillip Pendletonand Alexander Badalyan (University of South Australia) inmeasuring pore size distribution; Jan Skjemstad and EvelynKrull (CSIRO) for advice and comments on synthetic charproduction; Tasha Waller and Sonia Grocke (CSIRO) fortechnical support; and Dr. Ron Smernik (University of Adelaide)for helpful comments on the manuscript.

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Figure 5. Relationship between total pore volume and apparent hysteresisindex (H).

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(28) Sanchez-Camazano, M.; Sanchez-Martin, M. J.; Rodriguez-Cruz,M. S. Sodium dodecyl sulphate-enhanced desorption of atra-zine: effect of surfactant concentration and of organic mattercontent of soils.Chemosphere2000, 41, 1301-1305.

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(38) Huang, W. L.; Weber, W. J., Jr. A distributed reactivity modelfor sorption by soil and sediments. 10. Relationships betweendesorption, hysteresis, and the chemical characteristics of organicdomains.EnViron. Sci. Technol. 1997, 31, 2562-2569.

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(40) Yang, Y. N.; Sheng, G. Y.; Huang, M. Bioavailability of diuronin soil containing wheat-straw-derived char.Sci. Total EnViron.2006, 354, 170-178.

(41) Zhang, P.; Sheng, G. G.; Feng, Y.; Miller, D. M. Role of wheat-residue-derived char in the biodegradation of benzonitrile insoil: nutritional stimulation versus adsorptive inhibition.EnViron.Sci. Technol.2005, 39, 5442-5448.

(42) Ghosh, U.; Gillette, J. S.; Luthy, R. G.; Zare, R. N. Microscalelocation, characterization, and association of polycyclic aromatichydrocarbons on harbor sediment particles.EnViron. Sci. Technol.2000, 34, 1729-1736.

(43) Ahmad, R.; Kookana, R. S.; Alston, A. M.; Skjemstad, J. O.The nature of soil organic matter affects the sorption of pesti-cides. 1. Relationship with carbon chemistry as determined by13C CPMAS NMR spectroscopy.EnViron. Sci. Technol.2001,35, 878-884.

(44) Abelmann, K.; Kleineidam, S.; Knicker, H.; Grathwohl, P.;Kogel-Knabner, I. Sorption of HOC in soils with carbonaceouscontamination: Influence of organic-matter composition.J. PlantNutr. Soil Sci.2005, 168, 1-14.

(45) Lu, Y. F.; Pignatello, J. J. Demonstration of the “conditioningeffect” in soil organic matter in support of a pore deformationmechanism for sorption hysteresis.EnViron. Sci. Technol. 2002,36, 4553-4561.

Received for review May 12, 2006. Revised manuscript received August31, 2006. Accepted September 4, 2006.

JF061354Y


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www.elsevier.com/locate/scitotenv

Science of the Total Environm

Bioavailability of diuron in soil containing

wheat-straw-derived char

Yaning Yanga,c, Guangyao Shenga,T, Minsheng Huangb

aDepartment of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, AR 72701, U.S.A.bDepartment of Environmental Science and Technology, East China Normal University, Shanghai 200062, P.R. China

cDepartment of Civil and Environmental Engineering, University of Illinois, Urbana, IL 61801, U.S.A.

Received 19 October 2004; accepted 26 January 2005

Available online 23 March 2005

Abstract

This study evaluated the bioavailability of diuron in soil as influenced by char arising from the burning ofwheat straw. Thewheat

char was a highly effective sorbent for diuron. The presence of 1%wheat char in soil resulted in a 7–80 times higher diuron sorption.

A 10-week incubation resulted in b40% of 0.5 mg/kg diuron in 0.5% char-amended soil microbially degraded, as compared to 50%

in char-free soil under the same conditions. Over the experimental range of diuron application rates from 0 to 12 mg/kg and of char

contents from 0% to 1.0%, a 4-week bioassay indicated that both the barnyardgrass survival rating and the fresh weight of

aboveground biomass decreasedwith increasing diuron application at given char contents but increasedwith increasing char content

at potentially damaging diuron application rates. Residual analyses of bioassayed soils showed that the soils with char contents of

0.5% and higher and diuron application rates of 3.0mg/kg and higher, as compared to thosewith no or low (0.05%) char and a diuron

application rate of 1.5 mg/kg, had higher residual diuron levels but higher barnyardgrass survival ratings and fresh weights. These

results suggest that enhanced sorption of diuron in soil in the presence of wheat char reduced the bioavailability of diuron, as

manifested by reduced microbial degradation of diuron and its herbicidal efficacy to barnyardgrass. This study may have greater

implication than for burning of wheat straw that field burning of vegetations may reduce bioavailability of pesticides.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Bioavailability; Diuron; Microorganism; Barnyardgrass; Sorption; Wheat char

1. Introduction

Many studies have suggested that soil-bound

organic contaminants are unavailable for microbial

0048-9697/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.scitotenv.2005.01.026

T Corresponding author. Tel.: +1 479 575 6752; fax: +1 479 575

3975.

E-mail address: [email protected] (G. Sheng).

degradation (Ogram et al., 1985; Shimp and Young,

1988; Steen et al., 1980). Although recent research

suggested that limited biodegradation of soil-sorbed

pesticides may occur (Feng et al., 2000; Park et al.,

2001, 2002, 2003), liquid-phase contaminants are

much more bioaccessible to soil microorganisms

(Ogram et al., 1985; Guerin and Boyd, 1992; Lahlou

and Ortega-Calvo, 1999). Other studies have estab-

ent 354 (2006) 170–178

Y. Yang et al. / Science of the Total Environment 354 (2006) 170–178 171

lished that phytotoxicity of herbicides is directly

related to their concentrations in the soil solution

(e.g., Lambert, 1966; Pillay and Tchan, 1971). It is

generally true that only dissolved nutrients and

organic chemicals in the soil interstitial bulk-like

water (i.e., plant-available water above the wilting

point) are available for plant-root uptake. Sorption

largely controls concentrations of organic contami-

nants in the soil solution and thus is the major

determinant of the bioavailability of pesticides to both

microorganisms and plants. Enhancing sorption by

increasing soil organic matter content leading to a

reduction in the solution-phase concentrations results

in a decreased microbial degradation of organic

contaminants (e.g., Guerin and Boyd, 1993). Charcoal

dipping or banding effectively protects many plants

from herbicidal injury (Arle et al., 1948; Burr et al.,

1972; Chandler et al., 1978; Jordan and Smith, 1971;

William and Romanowski, 1972).

Sorptive properties of agricultural soils, and thus

bioavailability of pesticides, are often influenced by

agricultural practices. Field burning of crop residues

worldwide incorporates the resulting chars into soils.

Hilton and Yuen (1963) postulated that the retained

sorptivity of many Hawaiian soils for ureas and s-

triazines after oxidative removal of soil organic matter

by hydrogen peroxide was a result of the peroxide-

resistant soil chars arising from burning of sugarcane

trash. Toth et al. (1999) observed a reduction in the

phytotoxicity of diuron applied over the ash of

recently burned kangaroo grass, due primarily to the

diuron sorption by the ash. We confirmed their

postulation by measuring the sorption of pesticides

on soil-free chars from burning of crop residues.

Sorption of diuron by the chars from burning of wheat

straw and rice residue was 400–2500 times higher

than that by a soil with 2.1% organic matter (Yang and

Sheng, 2003a). Amendment of the soil with the wheat

char up to 1% (by weight) enhanced the sorptivity of

the soil for diuron in proportion to the char content.

The char aged in the soil for one month remained

highly effective for diuron sorption and dominated the

sorption, although a small reduction (b30%) in

sorptivity was observed (Yang and Sheng, 2003b).

Further aging of the char for up to 12 months did not

result in a further sorptivity reduction, indicating that

the char was resistant to degradation. One direct

consequence of the high sorptivity of crop-residue-

derived chars may be the reduced bioavailability of

pesticides in soils to both microbes and plants. The

reduction in microbial degradation of benzonitrile in a

soil in the presence of wheat char has been reported

(Zhang et al., 2004). Reduced microbial degradation

increases the persistence of pesticides and thus the

environmental risk associated with pesticide use. The

high sorptivity of crop-residue-derived chars may also

reduce herbicidal efficacy to weeds. Poor herbicidal

efficacy is a concern both economically and environ-

mentally due to additional application of herbicides

for weed control.

In this study, we determined the bioavailability of

diuron to soil microorganisms and to barnyardgrass

(Echinochloa crus-galli (L.) Beauv.) in soil in the

presence of wheat-straw-derived char. Use of bar-

nyardgrass, a common rice weed, has both agronomic

and environmental significance. Our objectives were

to determine the microbial degradation of diuron and

its efficacy to barnyardgrass in relation to soil

sorption in the presence of wheat char and to evaluate

the impact of crop-residue-derived chars on the

bioavailability of pesticides in soil. Results from

laboratory measurements and greenhouse bioassays

indicated that wheat char was a highly effective

sorbent for diuron and its presence in soil resulted in

enhanced diuron sorption and subsequently dimin-

ished bioavailability.

2. Materials and methods

2.1. Materials

Wheat char used in this study was from our

previous studies (Yang and Sheng, 2003a,b). Air-

dried wheat (Triticum aestivum L.) straw (10 kg) was

collected from the Arkansas Agricultural Research

and Extension Center in Fayetteville, Arkansas.

Wheat char was obtained by burning the straw on a

stainless steel plate (1 m � 1 m) in an open field under

natural conditions in a July afternoon. The BET

surface area of the char was determined to be 10.1 m2/

g in a commercial service laboratory. Chemical

analysis showed that the char contained 13% elemen-

tal carbon and 42% silica.

Soil, classified as Stuttgart silt loam, was collected

at the Rice Research and Extension Center, Stuttgart,

Y. Yang et al. / Science of the Total Environment 354 (2006) 170–178172

Arkansas. The soil had a mechanical composition of

17.1% sand, 60.4% silt, and 22.5% clay. The soil

contained 2.1% organic matter and had a cation-

exchange capacity of 8.5 cmolc/kg. The soil, without

records of crop residue burns, was presumed to contain

minimal levels of chars. The soil was air-dried, ground,

and passed through a 1-mm sieve. Char-amended soils

were prepared by thoroughly mixing soil with accu-

rately weighed char in exact char contents of 0.05%,

0.1%, 0.5%, and 1.0% (by weight).

Diuron with a purity of 99% was purchased from

ChemService (West Chester, PA) and used as received.

Diuron is an electroneutral molecule. The pesticide has

a water solubility of ~42 mg/l and a log Kow of 2.68 at

room temperature (Howard and Meylan, 1997). The

Henry’s Law constant of 2.7�10�6 atm m3/mol

indicates that the pesticide is non-volatile and therefore

suitable for prolonged laboratory and greenhouse

studies. Diuron is a urea compound primarily used as

a preemergence herbicide in soils to control germinat-

ing grasses and broad-leaved weeds. As a photosyn-

thesis inhibitor, diuron injures weeds with symptoms

of foliar chlorosis concentrated around veins (some-

times interveinal) followed by necrosis.

A mixed diuron-degrading culture was isolated

from soil collected in a cotton field where diuron has

been applied annually for over 15 years. One gram of

the soil was inoculated into 100 ml of medium

containing mineral salts (Stanier et al., 1966), 0.1 ml

of vitamin solution (Wolin et al., 1963), and saturated

diuron. The mixture was incubated for 1 week at 28

8C on a platform shaker at 150 rpm. After two serial

transfers to fresh medium, the culture enrichment was

obtained. Preliminary tests showed that the isolated

culture readily degraded diuron in solution.

Barnyardgrass seeds, collected from the plant

grown in a rice field in Stuttgart, AR in 1983, were

acid-scarified in 1 N nitric acid for 1 h at room

temperature. The seeds were washed with deionized

water, spread evenly on filter paper in petri dishes,

covered with another filter paper, watered with 3 ml of

deionized water, and incubated in the dark at room

temperature for 72 h for germination.

2.2. Sorption isotherms for diuron

Sorption of diuron by soil, wheat char, and 1%

char-amended soil was measured by the batch

equilibration technique. Various quantities of diuron

in 0.005 M CaCl2 solution were added into 25-ml

Corex glass centrifuge tubes containing sorbents with

a constant mass between 0.01 and 3.5 g. The mass of

sorbents was adjusted to allow for N40% of added

diuron to be adsorbed. Additional 0.005 M CaCl2solution was added to bring the total liquid volume to

10 ml. Initial concentrations of diuron ranged from

1.25 to 12.5 mg/l. The tubes were closed with Teflon-

lined screw caps and rotated (40 rpm) at room

temperature (~25 8C) for 48 h. Other measurements

have shown that sorption of diuron by both the soil

and the char reached apparent equilibria within 24 h;

the sorption by char-amended soil was thus assumed

to also reach equilibrium within the same duration.

After the establishment of sorption equilibria,

sorbents and aqueous phases were separated by

centrifugation at 6000 rpm (RCF=5210 g) for 30

min. The diuron concentrations in supernatants were

analyzed by high-performance liquid chromatography

(HPLC). The amount of diuron sorbed was calculated

from the difference between the amount initially

added and that remaining in equilibrium solution.

All measurements were in duplicate with a variation

generally b5%, and the calculated average data were

reported. The measurements with blanks not contain-

ing sorbents found that glass tubes did not adsorb

diuron and no processes other than sorption con-

tributed to the loss of solution-phase diuron.

2.3. Microbial degradation of diuron

Sterilized soil and 0.5% char-amended soil (200 g

each) were placed in 1000-ml glass beakers, spiked

with 2 ml of 50 mg/l diuron stock solution in acetone,

thoroughly mixed, and allowed for acetone to

evaporate for 2 days. The soils were then watered

to near the field capacity and aged for another 2 days

to allow the diuron sorption to complete. Three 5-g

samples from each of the soils were extracted with 5

ml of H2O and 5 ml of water-saturated ethyl acetate

for 72 h. Following the phase separation, 2 ml of

ethyl acetate were dried under N2 gas and redissolved

in 1 ml of methanol. The diuron concentrations in

methanol were analyzed by HPLC. The recoveries

were 95.2% and 85.2% for soil and char-amended

soil, respectively. Each soil was inoculated with 5 ml

of the isolated culture enrichment. Preliminary tests


found that 5 ml of the enrichment in 200 g of soil

gave an appreciable degree of diuron degradation in

one week. The soils were thoroughly mixed again.

The beakers were then covered with aluminum foil

and placed in the dark at room temperature. Three 5-g

soil samples from each beaker were taken weekly for

10 weeks for diuron analysis. The soils were

extracted following the same extraction procedures

as those for the recoveries, except that extracting

water contained 0.5% Ag2SO4 to immediately termi-

nate biodegradation. The diuron concentrations were

adjusted for the recoveries. The soils, watered when

necessary, were maintained moist throughout the

degradation experiment.

2.4. Barnyardgrass bioassay for diuron

A series of 4 diuron solutions with concentrations

of 60, 120, 240, and 480 mg/l in acetone were

prepared. Five milliliters of each of the solutions,

along with acetone only, were added to 200 g of char-

free soil or char-amended soils in plastic bags,

resulting in the diuron levels of 0, 1.5, 3.0, 6.0, and

12 mg/kg in the soils, respectively. The five diuron

levels were referred to as 0X, 1X, 2X, 4X, and 8X,

where X=1.5 mg/kg and is within the range of

recommended field application rates. The five char

contents were 0%, 0.05%, 0.1%, 0.5%, and 1%. The

combination of the 5 diuron rates and the 5 char

contents resulted in a total of 25 treatments. Each

treatment was in triplicate. The soils were thoroughly

mixed in the bags, and transferred to plastic cups

following the evaporation of acetone from the opened

bags.

A small quantity of soil (~20 g) was first removed

from each cup. Ten pregerminated barnyardgrass

seeds with extended radicles and hypocotyls were

placed evenly on the soil surface in each cup and then

covered with the previously removed soil. Following

planting, the cups were placed in a completely

randomized block design in a greenhouse, watered

with 40 ml of deionized water, and maintained moist

throughout the experiment. The greenhouse was

maintained at 34/20 8C day/night temperatures with

a 14-h lighting cycle. Barnyardgrass seedling survival

was visually rated two weeks after planting as percent

of survival between 0 and 100, with 0% representing

no survival and 100% complete survival (no injury).

The survival rating was performed independently by

three individuals. Average survival ratings were

calculated using the data from the replicated samples

from all the individuals. Four weeks after planting,

plants were cut at the soil level and immediately

weighed to obtain the fresh weights of the above-

ground biomass. All the visual survival rating and

fresh weight data were statistically analyzed using the

SAS program.

Following the bioassay, the soil samples of selected

treatments were analyzed for residual diuron by

HPLC using the extraction procedures described

earlier. The average diuron concentration of the

replicate soils of the same treatment was reported.

The soils from the following 6 treatments were

selected based on the char contents, diuron rates,

and barnyardgrass aboveground fresh weights: S0-0,

S0-1.5, S0.05-1.5, S0.5-3.0, S1-3.0, and S1-6.0,

where the suffix C-D to S represents the char content

(C)-applied soil concentration of diuron (D).

2.5. Analysis of diuron

Diuron in the supernatants from sorption experi-

ments and in the extracts from microbial degradation

and greenhouse bioassay tests was analyzed on a

Hitachi reversed-phase high-performance liquid chro-

matograph (Hitachi High-Technologies Tokyo,

Japan) fitted with a UV-visible detector set at the

maximum absorption wavelength for diuron (252

nm). A Phenomenex Prodigy C18 column was used

(Alltech Assoc., Deerfield, IL). The mobile phase

was a mixture of acetonitrile and water (50:50, v/v)

at a flow rate of 1.0 ml/min. The injection volume

was 20 Al.

3. Results and discussion

Isotherms for the sorption of diuron by soil, wheat

char and 1% char-amended soil are presented in Fig.

1, in which the amount of diuron sorbed (mg/kg) is

plotted against the equilibrium concentration (mg/l) in

water. No single mathematical models provided

adequate fits for the sorption data. The curves were

drawn to assist in visualization and comparison of the

data. Soil effectively sorbed diuron, rather consistent

with the prediction from the log Kow value of diuron

Incubation Time (days)

0 20 40 60 80

Diu

ron

Deg

rade

d (%

)

0

10

20

30

40

50

60

Soil0.5% Wheat Char in Soil

Fig. 2. Microbial degradation of diuron over time in sterilized soi

and char-amended soil inoculated with a mixed enrichment culture

Equilibrium Concentration (mg/L)

0 2 4 6 8 100

20

40

60

80

100Soil1% Wheat Char in Soil

0 2 4 60

3000

6000

9000

Wheat Char

Am

ount

of D

iuro

n S

orbe

d (m

g/kg

)

Fig. 1. Isotherms for sorption of diuron from water by soil, wheat

char, and char-amended soil.


and the soil organic matter content. Wheat char had a

much higher sorptivity than soil for diuron (see the

inset in Fig. 1). From the curves, we estimated that the

char was 700–37,000 times more effective than the

soil in sorbing diuron over the experimental concen-

tration range (0–6 mg/l). These results are similar to

those obtained in our previous study (Yang and

Sheng, 2003a). It has also been reported in the

literature that chars (the term ash was used) derived

from burning of vegetation are effective adsorbents

for pesticides (Yang and Sheng, 2003b; Toth and

Milham, 1975).

Much higher sorptivity of wheat char than of soil

resulted in enhanced sorption of diuron by the soil in

the presence of the char, as indicated in Fig. 1.

Calculations show that 1% char-amended soil sorbed

about 7–80 times more diuron than char-free soil over

the experimental concentration range. Assuming that

the amendment of soil with 1% char did not change

the sorptivity of the soil for diuron, 1% char

contributed N86% to the total sorption of diuron,

indicating the predominance of the char for diuron

sorption. Normalization of the sorption to char content

resulted in a diuron isotherm slightly lower than that

for soil-free char, which may have resulted from the

competitive sorption of dissolved soil organic matter

on the char. While the diuron sorption by char-

amended soil was evaluated with only one char

content, enhanced sorption at other char contents is

expected. At recommended field application rates,

enhanced diuron sorption in the presence of wheat

char may decrease the concentration of diuron in the

soil solution, leading to reduced biodegradation and

loss of herbicidal efficacy.

An evaluation of the bioavailability of diuron to

soil microorganisms in the presence and absence of

wheat char in soil was made by comparing the

degradation of diuron in char-free soil and 0.5%

char-amended soil, both inoculated with the same size

of an isolated diuron-degrading culture. The initial

diuron concentration in both soils was 0.5 mg/kg. We

simply measured the dissipation of diuron over

incubation time and did not identify the degradation

products, thus offering no mechanistical information

on the diuron transformation reaction. In Fig. 2, the

degradation is expressed as the percent of total diuron

degraded at given time. Although diuron is a rather

persistent pesticide in field soils, it slowly degraded in

field soils (Hill et al., 1955). It has been reported that

mixed cultures from pond water and sediment aerobi-

cally degraded diuron to several identified products

and carbon dioxide (Ellis and Camper, 1982). While

we did not know the species and the population of the

isolated cultures, diuron in both soils was degraded

with time. The degradation was slower in char-

amended soil than in char-free soil. Over a 10-week

incubation, b40% of diuron in 0.5% char-amended

soil was degraded, in comparison to about 55% in

char-free soil. While direct degradation of soil-sorbed

organic compounds by bacteria may occur, we did not

know whether such a process was involved in diuron

degradation. However, our results clearly show that

l

.


enhanced sorption in the presence of wheat char

reduced the bioavailability of diuron to soil micro-

organisms. Reduced biodegradation of benzonitrile by

a bacterium in soil in the presence of wheat char was

also due to enhanced sorption (Zhang et al., 2004). In

addition to elemental carbon and silica, wheat char

contained 21% potassium, 1.5% phosphorous, 0.64%

nitrogen, and other microelements (Yang and Sheng,

2003b). When in their available forms in soil, some of

these nutrients may stimulate microbial activity. We

have found that when benzonitrile was not limiting,

1% wheat char provided nutritional stimulation on

benzonitrile degradation (data not shown). Such a

stimulation on diuron degradation in 0.5% char-

amended soil was not obvious.

Fig. 3 is the photograph comparing the barnyard-

grass growth among the soil samples subjected to

diuron applications in the absence and presence of

wheat char just prior to cutting the plants for their

fresh weights. The samples consisted of 25 cups, each

representing one of the three replicates for each of all

the treatments, and were placed de-randomized to aid

visualization. In the absence of diuron application,

barnyardgrass showed a normal growth without

observable growth stimulation by wheat char

nutrients. One week after planting, the barnyardgrass

injury was obvious (photograph not shown). The

injury increased with increasing diuron application

Application Rate of Diuron (0.0 1.5 3.0 6

Fig. 3. Photograph showing barnyardgrass growth in soils as a function

planting.

rate at a given char content and decreased with

increasing char content at a given diuron application

rate. The observation is consistent with the earlier

sorption measurements that the presence of wheat

char enhanced the diuron sorption by soil. By four

weeks after planting (prior to cutting), uninjured

barnyardgrass showed continued growth, whereas

injured ones did not recover (Fig. 3).

More quantitative barnyardgrass bioassay to eval-

uate the impact of wheat char on the bioavailability of

diuron was obtained by visually rating barnyardgrass

survival two weeks after planting and by weighing

aboveground fresh biomass four weeks after planting

(Fig. 4). Without application of diuron, barnyardgrass

was somehow injured in char-free soil. In the presence

of wheat char (z0.05%), the injury was eliminated.

This suggests that unknown herbicides likely phyto-

toxic to barnyardgrass may be present in char-free soil

but deactivated by the char. A full rate of diuron (1.5

mg/kg) in char-free soil showed almost complete

injury to barnyardgrass. However, both the barnyard-

grass survival rating and fresh weight increased with

increasing char content. A char content of 0.5% or

higher was sufficiently high that diuron completely

lost its efficacy to barnyardgrass. The application rates

of 3 mg/kg and higher resulted in complete-to-partial

losses of diuron efficacy to barnyardgrass. Similar to

the observations with the full rate of diuron, the

Whe

at C

har

in S

oil (

%)

mg/kg).0 12

1.0

0.5

0.1

0.05

0.0

of diuron application rate and wheat char content four weeks after

Table 1

Relationship between measured residual concentrations of diuron

and barnyardgrass fresh weights in selected soil and char-amended

soil samples subjected to various treatments four weeks after

planting as influenced by percent char content and application rate

of diuron

Soil Char

content

(%)

Rate of

diuron fresh

weight (g)

Barnyardgrass

fresh weight (g)

Residual

concentration

(mg/kg)

S0-0 0 0 0.0242 0.00

S0-1.5 0 1.5 0.0007 0.73

S0.05-1.5 0.05 1.5 0.0030 0.69

S0.5-3.0 0.5 3.0 0.0224 1.28

S1-3.0 1 3.0 0.0308 1.20

S1-6.0 1 6.0 0.0378 2.42

0

20

40

60

80

100

Sur

viva

l Rat

ing

(%)

Cha

r Con

tent

(%)

Cha

r Con

tent

(%)

Rate of Diuron (mg/kg)

Rate of Diuron (mg/kg)

0.00

0.01

0.02

0.03

0.04

0.05

Fre

sh W

eigh

t (g)

00.05

0.10.5

1.0

00.05

0.10.5

1.0

01.5 3.0 6.0

12

01.5 3.0 6.0

12

(a) (b)

Fig. 4. Growth of barnyardgrass in soils as a function of diuron application rate and wheat char content showing (a) survival rating of

barnyardgrass two weeks after planting, and (b) fresh weight of barnyardgrass four weeks after planting.


survival rating and fresh weight at higher application

rates increased with increasing char content over the

tested range of char contents in soil. The Student’s t

test at the 95% level of confidence (a=0.05) was usedto compare the individual survival ratings and fresh

biomass weights at various char contents and diuron

application rates. Survival ratings and fresh weights

were statistically different (a=0.05) for V0.05% char

with no diuron application, for V0.5% char with 1.5

mg diuron/kg, for z0.1% char with 3.0 mg or 6.0 mg

diuron/kg (fresh weights were significantly different

forz0.5% char with 6.0 mg diuron/kg), and for

z0.5% char with 12 mg diuron/kg. These results

suggest the decreased bioavailability of diuron to

barnyardgrass with increasing char content in soil, due

presumably to enhanced sorption of diuron in the

presence of the char.

The sorptive role of wheat char in reducing diuron

bioavailability (efficacy) to barnyardgrass is con-

firmed by measuring residual concentrations of diuron

in soils after cutting barnyardgrass. Soils from 6

selected treatments, where barnyardgrass fresh

weights differed significantly, were analyzed for

residual diuron. The concentrations in the three

replicate soils of each treatment were highly invariant,

with the difference b4.3%. The average concentra-

tions were calculated and presented in Table 1. Char-

free soil (S0-0) did not contain a measurable level of

diuron. All other soils that had received diuron

contained residual diuron with levels of about 40–

49% of their respective application rates. The soils S0-

1.5 and S0.05-1.5 containing no or low char (0% and

0.05%, respectively) had residual diuron concentra-

tions of ~0.7 mg/kg and produced much lower

barnyardgrass fresh weights than the soil S0-0,

indicating the availability of diuron to barnyardgrass

in these soils. Although the soils S0.5-3.0 and S1-3.0

containing 0.5% and 1% char, respectively, had

residual diuron concentrations almost twice those in

the soils S0-1.5 and S0.05-1.5, the barnyardgrass

fresh weights associated with the former two soils

were much higher than those with the latter two. In

fact, the barnyardgrass fresh weights with the soils


S0.5-3.0 and S1-3.0 were similar to that with char-free

soil without receiving diuron application (i.e. the soil

S0-0). The barnyardgrass fresh weight with the soil

S1-6.0 containing an even higher level of residual

diuron remained high. These results indicate that

diuron in soils with high contents of wheat char was

largely unavailable to barnyardgrass.

Our measurements indicate that at typical applica-

tion rates of diuron, a char content of as low as 0.1%

may appreciably reduce the bioavailability of diuron

in soil. We reported that burning of wheat straw

produced wheat char at ~6% of the straw weight

(Yang and Sheng, 2003a). Using the average produc-

tion of wheat straw of ca. 6000 kg/ha, its burning

would generate ~360 kg/ha wheat char. If this wheat

char were mixed in soil with a density of 1.4 g/cm3 to

the depth of furrow slice (~0.15 m), a single burning

would result in a wheat char content of~0.02%. Crop-

residue-derived chars are expected to accumulate in

soils, as crop residues are repeatedly burned, and the

resulting chars are expected to remain to be highly

effective sorbents for pesticides (Yang and Sheng,

2003b). As such, field burning of crop residues may

effectively reduce the bioavailability of pesticides.

4. Conclusions

Wheat char is a highly effective sorbent for diuron.

Field burning of wheat straw incorporates the resulting

wheat char into soil and enhances the sorption of

diuron by the soil. A direct consequence of this

agricultural practice is the reduced bioavailability of

diuron in soil. We found that diuron was less

biodegradable in soil in the presence of wheat char.

Its herbicidal efficacy to barnyardgrass decreased with

increasing char content in soil and, at recommended

field application rates, could be completely lost when

the soil char content was 0.5% or higher. Reduced

bioavailability of diuron appeared to result from the

enhanced sorption in soil in the presence of wheat char.

Although only wheat char and diuron were tested in

this study, it is expected that chars arising from field

burning of other crop residues and vegetations also

effectively sorb other pesticides and reduce their

bioavailability. The presence of crop-residue-derived

chars in soil may increase the environmental risk of

pesticides and reduce their efficacy to pests.

Acknowledgments

This research was supported by USDA National

Research Initiative Competitive Grants Program

(Grant No. 2002-35107-12350).

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Simultaneous biodegradation of chloro-and methylthio-s-triazines usingcharcoal enriched with a newlydeveloped bacterial consortium

Ken-ichi YAMAZAKI,† Kazuhiro TAKAGI*,†,††

Kunihiko FUJII,††† Akio IWASAKI,†††

Naoki HARADA†††† and Tai UCHIMURA†

† Department of Applied Biology and Chemistry, Tokyo University ofAgriculture, Setagaya-ku, Tokyo 156–8502, Japan

†† Organochemicals Division, National Institute for Agro-Environmental Sciences, Tsukuba, Ibaraki 305–8604, Japan

††† Kowa Research Institute, Kowa Co., Ltd., Tsukuba, Ibaraki 305–0856, Japan

†††† Faculty of Agriculture, Niigata University, Nishi-ku, Niigata 950–2181, Japan

(Received February 18, 2008; Accepted April 10, 2008)

A special type of charcoal, Charcoal A100, was enriched with anewly developed bacterial consortium using a perfusion method.The bacterial consortium consisted of a methylthio-s-triazine-de-grading bacterium (Rhodococcus sp. FJ1117YT) and the chloro-s-triazine-degrading bacterial consortium CD7 (containingBradyrhizobium japonicam CSB1, Arthrobacter sp. CD7w andb-Proteobacteria CDB21). Enriched charcoal was capable of degrading chloro-s-triazines (simazine and atrazine) andmethylthio-s-triazines (simetryn and dimethametryn) simultane-ously in sulfur-free medium. Almost complete degradation wasobserved after 4-day cultivation of chloro-s-triazines and 9-daycultivation of methylthio-s-triazines. These triazines were miner-alized via their 2-hydroxy analogues.

Keywords: biodegradation, methylthio-s-triazines, chloro-s-tri-azines, bacterial consortium, Charcoal A100.

Introduction

The s-triazines are recognized as a major class of herbicides andare widely used in agriculture for controlling various weeds, andthey have been detected in ground and surface water.1–3) Amongthe removal technologies for such residual pesticides, bioremedi-ation is considered to be the most cost-effective and safe technol-ogy; therefore, many studies concerning s-triazine-degrading

bacteria have been reported.In our study, bacterial consortium CD74) was obtained which

can mineralize simazine, and a degrading bacterium b-Pro-teobacteria CDB21 was isolated from CD7 by Iwasaki et al.5) Itwas considered that CD7 was more effective for bioremediationthan strain CDB21 because strain CDB21 could not utilizesimazine for its growth in mineral salt medium withoutcyanocobalamin, but CD7 could utilize simazine as sole carbonand nitrogen sources in mineral salt medium.4,5) In addition, aspecial type of charcoal, Charcoal A100, enriched with CD7 wasdeveloped, and was placed under the subsoil of a golf course todegrade simazine. The simazine-degrading capability of the en-riched charcoal was maintained for nearly 2 years.4) Thus, Char-coal A100 enriched with CD7 is considered to be an effectivematerial for bioremediation; however, CD7 and strain CDB21could not degrade methylthio-s-triazines detected in riverwater,3,6) a lake basin,7) and river sediments,8) while Rhodococcussp. FJ1117YT9) can transform methylthio-s-triazines to their hy-droxyl analogues via sulfur oxidation, and accumulate hydroxy-s-triazines. It is considered that simultaneous degradation ofchloro- and methylthio-s-triazines using a mixture of these bacte-ria is meaningful because river water3,10) and river sediment3)

contamination with both triazines has been reported.To take advantage of these useful properties of CD7 and Char-

coal A100, this study describes the development of CharcoalA100 enriched with strain FJ1117YT and CD7, and demonstra-tion of the simultaneous degradation of chloro- and methylthio-s-triazines using this novel material.

Materials and Methods

1. MaterialsSimazine, atrazine, simetryn, and dimethametryn were purchasedfrom Kanto Kagaku. Cyanuric acid and simazine-2-hydroxy werepurchased from Dr. Ehrenstorfer GmbH. The sulfur-free mineralsalt medium (MM) used in this study contained Na2HPO4·12H2O1.2 g/l and KH2PO4 0.5 g/l. Prior to autoclaving, the medium wassupplemented with 10 ml/l of a sulfur-free solution of trace ele-ments, which contained MgCl2· 6H2O 2000 mg/l, FeCl2·H2O 200mg/l, ZnCl2 10 mg/l, MnCl2 5 mg/l, CoCl2 24 mg/l, CuCl2 5 mg/l,NiCl2· 6H2O 5 mg/l, Na2MoO4 5 mg/l, H3BO4 30 mg/l, Ca(OH)2

50 mg/l, and EDTA 500 mg/l. Mineral salt medium containingsulfate (MM�S) was also used. MM�S contained MgSO4 20mg/l and a solution of trace elements described by Yanze-Kontchou and Gschwind.11) MM and MM�S were supplementedwith s-triazines before autoclaving. Vitamin mixture was used asdescribed by Fujii et al.9)

2. Analytical methodsThe concentration of s-triazines in the medium was determinedusing HPLC (Tosoh) using the following method. Separation ofs-triazines was achieved at 40°C on an ODS column (Capcell PakC18 UG120 3�250 mm, 5 mm particle size; Shiseido) with a mo-

J. Pestic. Sci., 33(3), 266–270 (2008)DOI: 10.1584/jpestics.G08-08

Note

* To whom correspondence should be addressed.E-mail: [email protected] online July 14, 2008© Pesticide Science Society of Japan

bile phase containing a gradient mixture of acetonitrile and water(20%/80% 0 min–20%/80% 5 min, linear gradient–40%/60% 11min, and linear gradient–20%/80% 15 min–20%/80% 20 min).The injection volume was 50 m l and the eluted compounds weredetected by UV at 220 nm. Metabolites of s-triazines were deter-mined using LC-ESI-MS. Separation was achieved using LC Al-liance 2695 (Waters) system equipped with the same ODS col-umn as above (40°C). A mixture of acetonitrile/0.2% acetic acidwas used as the eluent (5%/95% 0 min, linear gradient–50%/50%10 min–80%/20%10.1 min–80%/20% 15 min, and linear gradi-ent–5%/95% 20 min). The injection volume was 10 m l. The ESI-MS system was Quattro micro API (Waters) with the flow rate ofnebulization set at 100 l/h and the flow rate for desolvation gas(N2) set at 500 l/h. The respective temperatures of source and desolvation were set at 100 and 350°C; and capillary voltage was3.5 kV. Detection was performed by scanning between m/z 100and m/z 300 under cone voltage of 35 V in positive ion mode.Cyanuric acid was detected at m/z 128 [M�H]� under cone volt-age of 23 V in negative ion mode, and simazine-2-hydroxy wasm/z 184 [M�H]� under cone voltage of 35 V in positive ionmode.

3. Enrichment of Charcoal A100 with strain FJ1117YT andCD7

Charcoal A100 (Toyo Denka Kogyo) was used as the enrichmentmaterial. Enrichment of charcoal with a bacterial consortium wasperformed using a charcoal perfusion method, which was modi-fied from the soil perfusion method described by Audus.12) First,washed Charcoal A100 (7.5 g, dry weight) was packed in perfu-sion apparatus equipped with glass sintered filter, and then auto-claved. Subsequently, three pieces of stab cultures of CD7 on aMM agar plate containing 40 mg/l simazine were placed on thecharcoal, and the charcoal layer was covered with glass fiber filterpaper. Enrichment was performed in the dark at 25°C. MM (300ml) containing 5 mg/l simazine was perfused with air lift using anair pump for 14 days. The concentration of simazine in the perfu-sion fluid was determined by HPLC, and the perfusion fluid wasreplaced twice. After 14 days, the glass fiber filter paper was re-placed. A phosphate buffer suspension of strain FJ1117YT wasplaced on the filter paper. MM (300 ml) containing 5 mg/lsimazine, 5 mg/l simetryn was perfused under similar conditionsfor 21 days, and the perfusion fluid was replaced once during theperfusion process. Lastly, MM (300 ml) containing 5 mg/l sime-tryn was used as perfusion fluid for 38 days, and was replacedonce. The vitamin mixture was added twice. Total enrichmenttime was 73 days, and this material was used thereafter. Non-en-riched Charcoal A100 was also perfused as a control under thesame conditions.

4. Preparation of DNA and analysis of 16S rRNA geneAdherent bacteria on the surface of Charcoal A100 enriched withstrain FJ1117YT and CD7 were removed by sonication in phos-phate buffer for 2 min. Charcoal A100 inhabited with strainFJ1117YT and CD7 was pulverized, and total DNA was ex-tracted with Fast DNA Kit for soil (Q-Bio gene). Total DNA of

strain FJ1117YT and each member of CD7 were extracted fromsuspensions of bacterial colonies grown on R2A agar (Difco)plates by a protocol for gram-positive bacteria of DNeasy Blood& Tissue Kit (QIAGEN). Nucleotide sequences of 16S rRNAgenes of isolated bacteria were analyzed by direct sequencing ofthe PCR products described previously.5)

5. Denaturing gradient gel electrophoresis (DGGE) analy-sis

Touchdown PCR was performed with a TP600 thermal cycler(Takara BIO) using GoTaq Green Master Mix (Promega). GM5F-gc-clamp and R534,13) primers designed from a sequence of thevariable V3 region of 16S rRNA, were used for PCR. DGGEanalysis was performed using 6% polyacrylamide gel (ratio ofacrylamide to bisacrylamide 37.5 : 1) in 1�TAE (40 mM Trisbase, 20 mM acetic acid, and 1 mM EDTA) with a 30% to 60%denaturant gradient (100% denaturant containing 7 M urea and40% formamide). Electrophoresis was performed at a constantvoltage of 150 V and at a temperature of 60°C for 3.5 h by usingthe DcodeTM universal mutation detection system (Bio-Rad).After electrophoresis was completed, the gel was stained withSYBR gold (Invitrogen) for 20 min, rinsed, and the bands werevisualized with a Molecular Imager Pharos FX plus system (Bio-Rad).

6. Simultaneous degradation of chloro- and methylthio-s-tri-azines using Charcoal A100 enriched with strainFJ1117YT and CD7

Charcoal A100 enriched with strain FJ1117YT and CD7 (0.4 gdry weight) was inoculated in MM (30 ml) containing 5 mg/leach of simazine, atrazine, simetryn, and dimethametryn or inMM�S containing 5 mg/l of each herbicide in 50 ml flasks. Theflasks were shaken at 120 rpm at 25°C for 15 days. As controls,sterile Charcoal A100 and/or Charcoal A100 enriched with onlyCD7 were inoculated and shaken under the same conditions. Theconcentration of s-triazines in the medium was determined peri-odically by HPLC. Cyanuric acid, simazine-2-hydroxy, and hy-droxy analogues of atrazine and dimethametryn in the mediumafter 15 days were measured by LC-ESI-MS.

Results and Discussion

1. Enrichment of Charcoal A100 with a bacterial consor-tium

The extent of enrichment of Charcoal A100 with strainFJ1117YT and CD7 was determined from the change in the con-centration of simazine and simetryn in the perfusion fluid. In thefirst step of enrichment, CD7 was enriched in Charcoal A100.Concentration of simazine in the CD7-inoculated charcoal de-creased faster than the control, and the degradation rate ofsimazine increased with every replacement of the perfusion fluid(data not shown). The charcoal was subsequently further enrichedwith strain FJ1117YT and perfused with MM containingsimazine and simetryn. Simazine was degraded almost immedi-ately (Fig. 1-A until Day21), in contrast to the slow degradationof simetryn (Fig. 1-B until Day21). The disappearance rate of

Vol. 33, No. 3, 266–270 (2008) Simultaneous biodegradation of chloro- and methylthio-s-triazines 267

simetryn was initialing almost the same as that of control, but in-creased after the second perfusion (Fig. 1-B on Day8). The de-crease of pesticides in sterile Charcoal A100 was considered tooccur because pesticides were adsorbed on Charcoal A100. Inorder to aid the growth of strain FJ1117YT,9) vitamin mixturewas added but had little effect on the enrichment of FJ1117YT.However, because the enrichment of CD7 was sufficient, MMcontaining simetryn without simazine was further perfused (Fig.1-B after Day21), and the degradation rate of simetryn was fur-ther increased. This result indicates the enrichment of strainFJ1117YT in Charcoal A100.

2. Detection of bacterial community in Charcoal A100 en-riched with strain FJ1117YT and CD7

Colony isolation from the bacterial consortium CD7 and subse-quent analyses of 16S rRNA genes revealed that CD7 consistedof Bradyrhizobium japonicam CSB1, Arthrobacter sp. CD7w andstrain CDB21. The presence of all members of CD7 and strainFJ1117YT enriched in Charcoal A100 were confirmed by PCR-DGGE analyses (Fig. 2).

3. Simultaneous degradation of chloro- and methylthio-s-tri-azines, and detection of their metabolites

Charcoal A100 enriched with strain FJ1117YT and CD7 was ap-plied to simultaneous degradation of chloro- and methylthio-s-tri-azines. Simazine and atrazine were degraded to by 80–100% withCharcoal A100 enriched with both strain FJ1117YT and CD7 orCD7 alone after 9 days, and were completely degraded after 15days (Fig. 3-A, B). On the other hand, simetryn and dimethame-tryn were degraded by over 80% with strain FJ1117YT and CD7enriched charcoal in sulfur-free medium, but they were not de-graded in the presence of sulfate (in MM�S) (Fig 3-C, D). In thesulfur-free medium with strain FJ1117YT and CD7 after 15 days,the concentrations of simazine-2-hydroxy and cyanuric acid were

less than 0.1 mg/l and hydroxy analogues of atrazine anddimethametryn were not detected (data not shown). This resultsuggests that hydroxyl analogues of methylthio-s-triazines, whichcan not be metabolized by strain FJ1117YT, were mineralized byCD7 via N-ammelide analogue and cyanuric acid. These resultsalso indicate that methylthio-s-triazines could be mineralized bythe bacterial consortium that included strain FJ1117YT and CD7.

In conclusion, the respective degradation abilities of CD7 andstrain FJ1117YT were successfully maintained in Charcoal

268 K.-i. Yamazaki et al. Journal of Pesticide Science

Fig. 1. Enrichment of strain FJ1117YT and CD7 in Charcoal A100 using a charcoal perfusion method. Changes in the concentrations ofsimazine (A) and simetryn (B) during enrichment are illustrated (both figures overlapped until 21 days). Charcoal A100 without enrichment wasused as a control. In order to enrich CD7, MM containing 5 mg/l simazine was perfused for 14 days before these data. The arrows indicate as fol-lows: replacement with MM containing simazine and simetryn (black), replacement with MM containing simetryn (white), and addition of vita-min mixture (striped).

Fig. 2. PCR-DGGE band profiles of bacterial strains inhabitingCharcoal A100. Each lane represents DNA samples extracted fromthe following specimens: Charcoal A-100 enriched with FJ1117YTand CD7 (A); FJ1117YT (B); CDB21 (C); CSB1 (D); and CD7w(E).

A100. Chloro- and methylthio-s-triazines were degraded simulta-neously and their metabolites were hardly detected. The expectedmetabolic pathways of chloro- and methylthio-s-triazines in themixed culture are shown in Fig. 4. Degradation of methylthio-s-triazines by the bacterial consortium, strain FJ1117YT and CD7,was suppressed by the presence of sulfate (Fig. 3) as well as theculture of strain FJ1117YT reported previously.9) However, Char-

coal A100 enriched with strain FJ1117YT and CD7 could be apromising model to construct a multifunctional material enrichedwith bacterial consortium for in situ bioremediation. On the basisof this study, we will attempt to construct another charcoal mate-rial, which will include methylthio-s-triazines-degrading bacteriathat are not suppressed by external sulfur sources.

Vol. 33, No. 3, 266–270 (2008) Simultaneous biodegradation of chloro- and methylthio-s-triazines 269

Fig. 3. Time course of simultaneous degradation of chloro- and methylthio-s-triazines with Charcoal A100 enriched with strain FJ1117YTand CD7. Degradation of simazine (A), atrazine (B), simetryn (C), and dimethametryn (D) by strain FJ1117YT and CD7 with (�) or without(�) sulfate, with CD7 alone (�), and using non-enriched Charcoal A100 as a control (�) are shown.

Fig. 4. The expected metabolic pathways of chloro- and methylthio-s-triazines degraded by CD7 (strain CDB21) and strain FJ1117YT.Simazine (R1, R2�C2H5) and atrazine [R1�C2H5, R2�CH(CH3)2] were selected as chloro-s-triazines, and simetryn (R1, R2�C2H5) anddimethametryn [R1�C2H5, R2�CH(CH3)CH(CH3)2] were used as methylthio-s-triazines in this study.

Acknowledgments

This work was supported in part by a Grant-in-aid (Hazardous Chem-icals) from the Ministry of Agriculture, Forestry, and Fisheries ofJapan (HC-05-2441-1).

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8) T. Kawakami, H. Eun, T. Arao, S. Endo, M. Ueji, K. Tamura andT. Higashi: J. Pestic. Sci. 31, 6–13 (2006).

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10) http://web.nies.go.jp/edc/edrep/report/1-1-2-1.htm (in Japanese)11) C. Yanze-Kontchou and N. Gschwind: Appl. Environ. Microbiol.

60, 4297–4302 (1994).12) L. J. Audus: Nature 158, 419–419 (1946).13) G. Muyzer, E. de Waal and A. Uitterlinden: Appl. Environ. Mi-

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270 K.-i. Yamazaki et al. Journal of Pesticide Science

Transactions of the ASABE

Vol. 51(6): 2061-2069 � 2008 American Society of Agricultural and Biological Engineers ISSN 0001-2351 2061

EFFECT OF LOW‐TEMPERATURE PYROLYSIS CONDITIONS

ON BIOCHAR FOR AGRICULTURAL USE

J. W. Gaskin, C. Steiner, K. Harris, K. C. Das, B. Bibens

ABSTRACT. The removal of crop residues for bio‐energy production reduces the formation of soil organic carbon (SOC) andtherefore can have negative impacts on soil fertility. Pyrolysis (thermoconversion of biomass under anaerobic conditions)generates liquid or gaseous fuels and a char (biochar) recalcitrant against decomposition. Biochar can be used to increaseSOC and cycle nutrients back into agricultural fields. In this case, crop residues can be used as a potential energy source aswell as to sequester carbon (C) and improve soil quality. To evaluate the agronomic potential of biochar, we analyzed biocharproduced from poultry litter, peanut hulls, and pine chips produced at 400°C and 500°C with or without steam activation.The C content of the biochar ranged from 40% in the poultry litter (PL) biochar to 78% in the pine chip (PC) biochar. Thetotal and Mehlich I extractable nutrient concentrations in the biochar were strongly influenced by feedstock. Feedstocknutrients (P, K, Ca, Mg) were concentrated in the biochar and were significantly higher in the biochars produced at 500°C.A large proportion of N was conserved in the biochar, ranging from 27.4% in the PL biochar to 89.6% in the PC biochar. Theamount of N conserved was inversely proportional to the feedstock N concentration. The cation exchange capacity wassignificantly higher in biochar produced at lower temperature. The results indicate that, depending on feedstock, somebiochars have potential to serve as nutrient sources as well as sequester C.

Keywords. Agricultural residues, Biochar, Bioenergy, Black carbon, Carbon sequestration, Charcoal, Plant nutrition,Pyrolysis, Soil fertility, Soil organic carbon.

yrolysis of crop residues to produce renewable ener‐gy is one option to reduce the use of fossil fuels. Py‐rolysis generates biochar, oil, and gas products thatcan all be used as fuels (Ioannidou and Zabaniotou,

2007). Pyrolytic biochar can also potentially be used as a low‐cost sorbent (Ioannidou and Zabaniotou, 2007) or as a soilamendment to improve soil fertility and sequester carbon(Lehmann et al., 2006; Steiner, 2007). Removal of crop resi‐dues for energy production can have deleterious effects onsoil organic carbon (SOC) and consequently on soil fertility(Lal, 2004). Pyrolysis of crop residues with C returned to thesoil in the form of biochar may help maintain or increasestable SOC pools and cycle nutrients back into agriculturalfields. Pyrolysis with biochar C sequestration may offer anoption to reduce the conflict between cultivating crops fordifferent purposes, e.g., energy vs. C sequestration or food.

There are several lines of evidence that charcoal plays animportant role in soil fertility. Charcoal has been identifiedas an important soil constituent in fertile Chernozems(Schmitdt et al., 1999) and in anthropogenic enriched dark

Submitted for review in August 2008 as manuscript number SW 7634;approved for publication by the Soil & Water Division of ASABE inNovember 2008.

The authors are Julia W. Gaskin, Sustainable Agriculture Coordinator,Christoph Steiner, Post‐Doctoral Associate, Keith Harris, Technician, K.C. Das, Associate Professor, and Brian Bibens, Research Engineer,Department of Biological and Agricultural Engineering, DriftmierEngineering Center, University of Georgia, Athens, Georgia.Corresponding author: Julia W. Gaskin, Department of Biological andAgricultural Engineering, Driftmier Engineering Center, University ofGeorgia, Athens, GA 30602; phone: 706‐542‐1401; fax: 706‐542‐1886;e‐mail: [email protected].

soil (Terra Preta) found throughout the lowland portion of theAmazon Basin (Glaser et al., 2000). Research on tropicalsoils indicates that charcoal amendments can increase andsustain soil fertility (Steiner et al., 2007). The beneficial ef‐fects appear to be related to alterations in soil physical, chem‐ical, and biological properties, such as reduced acidity(Topoliantz et al., 2005), increased cation exchange capacity(CEC) (Cheng et al., 2008; Liang et al., 2006), enhanced ni‐trogen (N) retention (Lehmann et al., 2003; Steiner et al.,2008b), increased microbiological activity (Steiner et al.,2008a), and increased mycorrhizal associations (Warnock etal., 2007). Research on the effect of wildfire charcoal in for‐est ecosystems indicates that it stimulates microbial activity(Pietikäinen et al., 2000) and influences nitrogen cycling(Berglund et al., 2004; DeLuca et al., 2006; Wardle et al.,1998). Research also indicates that charcoal is recalcitrant(Seiler and Crutzen, 1980), and it may persist for hundreds orthousands of years.

Charcoals produced from wildfire or traditional charcoalproduction may have different chemical and physical charac‐teristics from pyrolytic biochars created under specific con‐ditions for energy production. Both feedstock and pyrolysisconditions such as temperature and carrier gas affect thechemical and physical characteristics of biochar (Antal andGrønli, 2003; Bansal et al., 1988; Benaddi et al., 2000; Guoand Rockstraw, 2007a; Strelko et al., 2002). Most of the liter‐ature discusses high‐temperature biochars that are producedat greater than 500°C or activated carbon typically producedat 800°C. As pyrolysis temperatures increase, volatile com‐pounds in the biochar matrix are lost, surface area and ash in‐crease, but surface functional groups that can provideexchange capacity decrease (Guo and Rockstraw, 2007a).

P

2062 TRANSACTIONS OF THE ASABE

Pyrolysis of nutrient‐rich feedstock is likely to producenutrient‐rich biochar, but nutrient conservation and availabil‐ity in biochars is not well understood. Nutrients susceptibleto volatilization such as N are almost completely lost after aburn (Giardina et al., 2000). Whether elements are retainedduring pyrolysis, the availability of nutrients for plants, andthe effect of pyrolysis conditions on these characteristics areunclear. For biochar to be used in agriculture, a better under‐standing of its properties and how it affects soil fertility isneeded. Therefore, our objectives were to determine the ef‐fect of feedstock, temperature, and carrier gas on key charac‐teristics of biochar for agricultural use. Specifically, wewished to compare characteristics critical for agricultural useincluding pH, CEC, total nutrient concentrations, and poten‐tially available nutrient concentrations in biochars from threefeedstocks under two temperature regimes using two carriergases with and without secondary steam activation.

MATERIALS AND METHODSBIOCHAR PRODUCTION

We selected three common feedstocks to represent a rangeof physical properties and mineral content: raw poultry litterfrom broiler houses (Gallus domesticus, PL), pelletized pea‐nut hulls (Arachis hypogaea, PN), and raw pine chips (Pinustaeda, PC). Biochars were produced in a batch pyrolysis unitat two peak temperatures (400°C and 500°C) with eithersteam or nitrogen (N2) as a carrier gas. The biochars producedwith N2 as a carrier gas were produced with or without steamactivation at the original pyrolysis temperatures (400°C and500°C). Each of the production combinations (three feed‐stocks, three pyrolysis types, two temperatures = 18) was rep‐licated three times. The conversion efficiency was calculatedas the percentage of the feedstock input (dry weight, DW) andbiochar output (biochar DW / feedstock DW).

CHEMICAL ANALYSESBiochars were ground in a ball mill to pass a 300 �m sieve

before nutrient analysis. Feedstock and the biochars wereanalyzed for total C, N, and sulfur (S) by dry combustion(CNS‐2000, Leco Corp., St. Joseph, Mich.). Total mineralswere extracted using a closed‐vessel microwave digestionwith HNO3 (USEPA method 3050; USEPA, 1994). A Meh‐lich I extraction (0.05 M HCl + 0.0125 M H2SO4) (Mehlich,1953) was also used on biochar samples as an index of poten‐tially plant‐available nutrients. Aluminum, Cu, Ca, Fe, Mg,Mn, P, K, Na, and Zn were measured by inductively coupledplasma spectrometry (ICP, Thermo Jarrell‐Ash model 61E,Thermo Fisher Scientific, Waltham, Mass.).

Biochar pH was measured in deionized water using a 1 to5 wt/wt ratio. Samples were thoroughly mixed and allowedto equilibrate for 1 h. The pH was measured with a digital pHmeter (AR15, Thermo Fisher Scientific, Waltham, Mass.).

Cation exchange capacity of the biochar was measured bya modified ammonium‐acetate compulsory displacement

(Sumner and Miller, 1996). Samples were leached with de‐ionized water five times before starting the CEC extractionto reduce interference from soluble salts. Twenty mL of de‐ionized water was added to a 1 g sample of biochar in a dis‐posable nalgene 0.45 �m cellulose nitrile filter flask. Theflask was placed on an orbital shaker and shaken at 180 rpmfor 5 minutes. The sample was vacuum filtered, and the lea‐chate was saved for further analysis. After the fifth wash,10�mL of Na‐acetate (pH 7) was added to the sample, and themixture shaken for 10 min. This process was repeated threetimes to ensure that exchange sites were saturated with Naions. Biochar samples were then washed three times withethanol to remove excess Na. Sodium ions were displacedwith NH4‐acetate (pH 7) three times and measured by atomicadsorption (PE 4100ZL, Perkin Elmer, Waltham, Mass.).

The reserved leachate from the five washings (CEC proce‐dure above) was composited and analyzed for dissolved car‐bon (DC), dissolved inorganic carbon (DIC), ammonium‐nitrogen (NH4-N), and nitrate‐nitrogen (NO3

-N). Dissolvedcarbon and DIC was measured by combustion (ShimadzuTOC‐5050A, Shimadzu, Columbia, Md.). Dissolved organicC (DOC) was calculated by difference (DOC = DC - DIC).Nitrate‐nitrogen and NH4-N were analyzed on anautoanalyzer using cadmium reduction and phenatecolorimetric methods (EnviroFlow 3000, Perstorp, Toledo,Ohio).

STATISTICAL ANALYSESTreatment effects were analyzed by general linear model

(GLM) univariate analysis of variance (ANOVA). Thedetection limit was used for results below the detection limit,if other results were above the limit. This allowed aconservative estimate of the elemental concentration of thebiochar. If all results were below the detection limit, then nostatistical analysis was performed. Significant differences(p�< 0.05) between the feedstock and treatments wereseparated by the Tukey test. Statistical analyses and plotswere performed using SPSS 12.0 and SigmaPlot 8.02 (SPSS,Inc., Chicago, Ill.).

RESULTS AND DISCUSSIONSteam pyrolysis of the peanut hull pellets in the batch reactor

presented difficulties due to excessive swelling by the peanuthull feedstock that clogged the reactor. Low‐temperature steampyrolysis in a batch reactor may not be appropriate for thisfeedstock. Analysis of PC and PL biochars revealed nodifference in total nutrients, Mehlich I extractable nutrients,CEC, or pH between steam and N2 as carrier gas; consequently,we report on the results from pyrolysis with the N2 carrier gaswith or without subsequent steam activation.

INFLUENCE OF FEEDSTOCK

The total element concentrations in the feedstock had thestrongest influence on the chemical composition of the

Table 1. Total element concentrations in the three agricultural feedstocks used for pyrolysis at 400°C and 500°C.

Feedstock

Values in g kg‐1 Values in mg kg‐1

C N P K S Ca Mg Al Fe Na Cd Cr Cu Mn B Mo Ni Zn

Poultry litter (PL) 326 45.1 19.5 29.5 5.8 28.0 5.66 6.32 3.91 9.27 1.4 7.3 381 377.0 49.9 3.5 8.0 414Peanut hulls (PN) 552 13.6 0.61 5.06 0.9 1.84 0.79 0.92 0.42 0.04 <1 2.0 36.5 44.0 15.2 15.6 1.5 20.2Pine chips (PC) 571 0.9 0.08 0.59 0 0.75 0.21 0.03 0.13 0.04 <1 2.1 1.7 13.8 2.1 <1.0 <2.0 47.8

2063Vol. 51(6): 2061-2069

Table 2a. Means and standard errors for pH, CEC, and total macronutrient concentrations in poultry litter, peanuthull, and pine chip biochars. Feedstock and temperature columns indicate significant differences (p < 0.05, n = 3).[a]

Poultry Litter (PL) Peanut Hulls (PN) Pine Chips (PC)

Feedstock

Temp.

400°C 500°C 400°C 500°C 400°C 500°C

Biochar SA Biochar SA Biochar SA Biochar SA Biochar SA Biochar SA

pH(S.U.)

10.1±0.04

10.1±0.07

9.74±0.05

9.88±0.09

10.5±0.05

10.5±0.10

10.1±0.02

9.96±0.01

7.55±0.09

7.99±0.09

8.30±0.15

8.10±0.60 PC<PL<PN

CEC(cmol kg‐1)

61.1±0.73

57.4±1.4

38.3±1.7

37.0±1.6

14.2±0.46

11.7±2.04

4.63±0.10

4.46±0.13

7.27±0.54

6.00±0.11

5.03±0.85

6.02±3.12 PC<PN<PL 500<400

C(g kg‐1)

392±3.8

399±7.4

392±8.6

421±23

732±14

762±3.4

804±1.7

806±5.8

739±17

761±3.6

817±1.9

820±17 PL<PN, PC 400<500

N(g kg‐1)

34.7±0.79

34.7±0.77

30.9±0.89

32.3±1.6

24.3±0.18

24.0±0.37

24.8±0.89

24.8±0.34

2.55±0.40

1.95±0.06

2.23±0.09

2.20±0.12 PC<PN<PL 500<400

P(g kg‐1)

30.1±0.16

32.2±2.3

35.9±1.6

34.8±2.6

1.83±0.11

1.70±0.12

1.97±0.03

2.06±0.11

0.15±0.004

0.14±0.004

0.14±0.02

0.20±0.02 PC<PN<PL 400<500

K(g kg‐1)

51.1±1.3

52.6±4.9

58.6±2.9

54.7±1.5

15.2±0.58

14.40±1.40

16.4±0.19

16.5±0.79

1.45±0.06

1.51±0.07

1.45±0.18

2.25±0.25 PC<PN<PL 400<500

Ca(g kg‐1)

42.7±0.30

45.7±3.0

50.4±2.2

49.1±3.7

4.62±0.06

4.46±0.29

5.12±0.12

5.21±0.20

1.71±0.11

1.69±0.02

1.85±0.14

2.17±0.04 PC<PN<PL 400<500

Mg(g kg‐1)

10.7±0.23

11.4±0.91

12.9±0.50

12.4±1.0

2.19±0.06

2.17±0.16

2.50±0.05

2.59±0.11

0.60±0.04

0.58±0.03

0.59±0.06

0.76±0.01 PC<PN<PL 400<500

S(g kg‐1)

13.67±0.39

12.3±0.09

13.93±1.1

13.9±0.37

0.56±0.02

0.51±0.03

0.55±0.09

0.37±0.09

0.01±0.04

0.16±0.05

0.06±0.01

0.08±0.04 PC, PN<PL

[a] SA = steam activation.

Table 2b. Means and standard errors for total micronutrient and selected element concentrations in poultry litter, peanuthull, and pine chip biochars. Feedstock and temperature columns indicate significant differences (p < 0.05, n = 3).[a]

Poultry Litter (PL) Peanut Hulls (PN) Pine Chips (PC) Feedstock Temp.

400°C 500°C 400°C 500°C 400°C 500°C


Al(g kg‐1)

9.87±1.36

8.12±1.59

13.02±0.36

14.25±1.97

2.40±0.07

2.33±0.16

2.73±0.05

2.81±0.13

0.07±0.01

0.05±0.005

0.07±0.01

0.06±0.008 PC, PN<PL 400<500

Fe(g kg‐1)

6.06±0.52

5.55±0.42

8.03±0.55

8.89±1.27

1.00±0.02

0.97±0.07

1.15±0.02

1.20±0.06

0.15±0.11

0.04±0.007

0.05±0.01

0.20±0.07 PC, PN<PL 400<500

Na(g kg‐1)

15.1±0.31

15.8±1.37

17.2±1.02

16.6±1.12

0.026±0.001

0.028±0.006

0.035±0.004

0.044±0.005

<0.014±0.004

0.053±0.032

0.013±0.002

0.075±0.054 PN, PC<PL

B(mg kg‐1)

91.5±3.16

96.0±8.25

100±0.31

93.0±3.98

32.5±1.57

29.9±2.87

33.7±0.27

34.1±1.15

5.69±0.30

6.69±0.21

4.21±0.62

6.94±1.33 PC<PN<PL

Cd(mg kg‐1)

2.75±0.73

<2.65±0.83 <1

<1.10±0.10

<1.35±0.35

<1.35±0.35 <1 <1 <1 <1 <1 <1

Cr(mg kg‐1)

28.0±4.1

28.8±5.2

59.4±3.3

56.1±4.5

3.95±0.31

3.00±0.57

3.63±0.31

3.94±0.16 <1

1.23±0.09

3.43±0.88

17.7±5.9 PN, PC<PL 400<500

Cu(mg kg‐1)

805±23

880±49

1034±68

943±81

16±0.60

13±1.27

19±0.50

19±1.84

25±7.03

10±6.18

9±2.34

13±5.57 PC, PN<PL 400<500

Mn(mg kg‐1)

596±5.6

637±37

725±29

697±46

116±2.3

116±8.0

131±2.3

136±5.7

274±9.3

269±7.8

258±30

350±4.0 PN<PC<PL 400<500

Mo(mg kg‐1)

17.1±5.3

12.1±0.41

14.2±1.1

13.8±1.2

4.78±3.6 <1 <1 <1 <1 <1 <1

<4.11±3.11 PC, PN<PL

Ni(mg kg‐1)

13.6±0.00

19.5±3.7

20.3±1.1

29.1±8.4

<2.29±0.29

<2±0

<2±0

<10.4±8.0

<2±0

<2±0

<2.91±0.55

17.5±14.7 PC, PN<PL

Zn(mg kg‐1)

628±12

680±41

752±28

728±50

35±2.2

31±2.9

37±2.1

36±0.00

15±1.1

16±0.7

18±0.6

20±2.4 PC, PN<PL 400<500

[a] SA = steam activation; < indicates mean contains results below the detection limit; ±0.00 indicates all results were near instrument detection limit.

biochar. Concentrations of plant nutrients in the feedstocksgenerally followed the pattern of PC < PN < PL. Feedstockcarbon concentrations had the opposite pattern, with PL < PN< PC (table 1).

There were significant differences in C concentrations inthe biochar, with PL containing less C than the PN or PCbiochar (table 2a). The nutrient‐rich poultry litter containsrelatively more minerals than the other feedstocks, which

decreases the C content. Nitrogen, P, K, Ca, and Mgconcentrations in the biochar were significantly different,with PC < PN < PL (table�2a). The concentration of themicronutrients B, Cu, Fe, Mn, Na, and Zn were significantlyhigher in PL biochar (p < 0.05), but there were no differencesdetected between the PN and PC biochars except for Mn(table 2b). Concentrations of metals such as Al, Cr, Ni, andMo were low. The PL biochar contained the highest


Figure 1. Percentages with standard errors of feedstock nutrients conserved in the biochar and percentages of total nutrients that were Mehlich Iextractable at two pyrolysis temperatures and in three biochars. Letters above the columns indicate significant difference of nutrients conservedbetween biochar types (p < 0.05, n = 3). Letters within columns indicate significant difference in the percentage of total nutrients that were Mehlich�Iextractable (p < 0.05, n = 3).

concentrations of these metals, as would be expected fromthe higher feedstock concentrations. Cadmium was belowthe detection limit in PC biochars and near or at the detectionlimits in PL and PN biochars (table 2b).

The amount of N conserved ranged from 27.4% in the PLbiochar to 89.6% in the PC biochar and was inverselyproportional to the feedstock N concentration (fig. 1b andtable 1). The higher N losses seen from the PL were likely dueto the volatilization of the poultry manure NH4-N and easilydecomposable N-containing organic compounds in themanure, such as uric acid. In contrast, the low concentrationof N in the PC feedstock is likely to be incorporated intocomplex structures that are not easily volatilized.

About 60% of the P in the PL and PC feedstock wasretained in the PL and PC biochar, while nearly 100% of theP in the PN feedstock was retained in the PN biochar (fig. 1c).

In general, the PL biochar had a lower proportion of nutrientsretained than the PN or the PC biochar (figs. 1c through 1f).This may be due to a higher proportion of some of theseelements retained in the aqueous/bio‐oil fraction in PLbiochar (K. C. Das, 2007, unpublished data, University ofGeorgia, Athens, Ga.).

The pattern of Mehlich I extractable concentrations wassimilar to that of the total nutrient concentrations (tables 3aand 3b). There were significant differences in Mehlich Iextractable P, K, Ca, and Mg concentrations, with PC < PN< PL. There were differences by feedstock in the percentageof the total nutrients that were Mehlich I extractable (figs. 1athrough 1f). Only 19% of the PL biochar P was Mehlich Iextractable compared to over 40% in the PN biochar (400°C,fig. 1c). About 90% of the PL biochar K was Mehlich Iextractable compared to only 45% in the PN biochar (400°C,

2065Vol. 51(6): 2061-2069

Table 3a. Means and standard errors of the Mehlich I macronutrient concentrations in poultry litter, peanut hull,and pine chip biochars. Feedstock and temperature columns indicate significant differences (p < 0.05, n = 3).[a]


400°C 500°C 400°C 500°C 400°C 500°C


P(g kg‐1)

5.58±0.31

4.09±1.22

5.33±0.18

4.66±0.20

0.76±0.02

0.67±0.06

0.57±0.04

0.59±0.03

0.03±0.002

0.034±0.004

0.04±0.008

0.06±0.03 PC<PN<PL

K(g kg‐1)

46.2±0.96

34.1±8.40

38.1±2.68

40.0±2.81

6.84±0.16

6.28±0.67

5.91±0.28

6.76±0.30

0.30±0.009

0.38±0.02

0.41±0.06

0.97±0.32 PC<PN<PL

Ca(g kg‐1)

3.34±0.84

1.95±0.82

2.21±0.36

1.63±0.13

1.68±0.02

1.48±0.15

1.19±0.06

1.22±0.06

0.30±0.04

0.31±0.05

0.43±0.10

0.39±0.16 PC<PN<PL

Mg(g kg‐1)

3.09±0.28

2.19±0.68

3.03±0.13

2.92±0.05

0.80±0.03

0.62±0.09

0.37±0.02

0.39±0.01

0.05±0.008

0.06±0.009

0.06±0.01

0.08±0.04 PC<PN<PL

[a] SA = steam activation.

Table 3b. Means and standard errors of the Mehlich I micronutrient and selected element concentrations in poultry litter,peanut hull, and pine chip biochars. Feedstock and temperature columns indicate significant differences (p < 0.05, n = 3).[a]

Poultry Litter (PL) Peanut Hulls (PN) Pine Hips (PC) Feedstock Temp.

400°C 500°C 400°C 500°C 400°C 500°C


Al(g kg‐1)

0.47±0.11

11.3±2.24

1.43±0.31

1.52±0.24

330±24

585±213

1129±32

1360±51

6.17±0.59

6.35±0.53

7.53±1.12

12.12±4.76 PL, PC<PN 400<500

Fe(g kg‐1)

0.66±0.21

3.16±0.08

0.06±0.007

0.19n = 1

140±2.2

142±18

197±3.8

221±11

3.72±0.26

4.58±0.19

14.6±2.89

33.3±8.39 PL, PC<PN 400<500

Na(g kg‐1)

9.57±0.19

7.08±1.61

6.98±0.43

7.24±0.07

0.02±0.001

0.02±0.002

0.02±0.58

0.03±0.002

0.03±0.002

0.03±0.002

0.03±0.005

0.08±0.037 PN, PC<PL

B(mg kg‐1)

16.7±1.59

18.8±2.05

18.67±0.85

20.4±0.59

4.20±0.12

4.96±1.08

3.97±0.22

5.84±0.66

0.45±0.04

0.41±0.07

0.52±0.07

1.15±0.49 PC<PN<PL

Cr(mg kg‐1)

0.19±0.03

0.19±0.02

0.14±0.01

0.11±0.01 <0.04 <0.04

0.41±0.04

0.52±0.03 <0.06 <0.06 <0.06 <0.06

Cu(mg kg‐1)

0.40±0.06

0.29±0.08

<0.08±0.02

<0.05±0.005

0.67±0.04

<0.59±0.32

<0.04±0.001 <0.04

6.55±2.18

2.48±0.68

2.70±0.89

3.82±3.34 PL, PN<PC

Mn(mg kg‐1)

7.69±1.23

8.64±1.28

6.75±1.03

5.17±0.43

24.7±0.70

21.2±2.33

14.4±0.45

16.3±0.71

22.6±2.61

25.2±3.79

24.1±6.67

36.2±12.5 PL<PN<PC

Mo(mg kg‐1)

0.87±0.19

1.11±0.22

1.42±0.14

1.94±0.19 <0.04 <0.04 <0.04 <0.04

0.15±0.002

0.25±0.06

0.11±0.03

0.65±0.35

Ni(mg kg‐1) <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 <0.2 <0.2 <0.2 <0.2

Zn(mg kg‐1)

0.06±0.01

0.30±0.02

0.05±0.07 <0.04

10.51±1.22

7.36±0.59

5.58±0.26

6.30±0.45

2.20±0.17

2.31±0.21

1.36±0.26

3.66±1.17 PL<PC<PN

[a] SA = steam activation; < indicates mean contains results below the detection limit.

fig. 1d). Manganese and Zn concentrations were significantlylower in the PL biochar than the PC or PN biochars. Copper,Al, and Fe was also lower in the PL biochar compared to thePN biochar. These patterns are the reverse of that seen in thefeedstock or the total element concentrations in the biochars.If pyrolysis can reduce P and other metal availability inpoultry litter, it may reduce some of the environmentalconcerns associated with land application of poultry litter.These results should be interpreted with caution. TheMehlich I extraction, which is a weak double acid extraction,may not have been strong enough to remove these acid‐soluble cations under the high pH conditions found in the PLbiochar.

The Mehlich I extraction was developed for acidic soils inthe southeastern U.S. with low CEC or base saturation (Kuo,1996), and it is the standard extraction used for plant‐available nutrients and fertilizer recommendations inAlabama, Georgia, Florida, South Carolina, Tennessee, andVirginia. In this study, Mehlich I extractable elementconcentrations were used as an index to compare the

potential for different biomass sources and productiontechniques to supply plant‐available nutrients. Theextraction has not been calibrated for biochar and may notreflect actual plant‐available nutrient concentrations.However, data from a greenhouse trial using pine chip andpeanut hull biochar amendment of three different Ultisols(Speir, 2008) and from a field trial with the same biochars(Gaskin et al., 2007) indicate an increase in Mehlich I K andMg in soils amended with peanut hull biochar. The increasedMehlich I K in the soil was reflected in an increase of thesenutrients in corn tissue (Zea mays) in the field trial.

The pH and CEC of the biochars were also significantlyinfluenced by feedstock (table 2a). All the biochars werebasic, with the highest pH seen in the PN biochar. Tryon(1948) reported increased soil pH with the addition of pineand hardwood charcoal. He attributed the greater pH increaseseen in the hardwood charcoal treatment to the higher ashcontent, in particular to the hydrolysis of salts of Ca, K, andMg in the presence of water. In this study, PC biochar hadboth the lowest total concentrations of these cations and the


Table 4. Means and standard errors of dissolved carbon (DC), dissolved inorganic carbon (DIC), dissolved organic carbon(DOC), ammonium‐nitrogen (NH4-N), and nitrate‐nitrogen (NO3-N) in leachate from poultry litter, peanut hull,and pine chip biochars. Feedstock and temperature columns indicate significant differences (p < 0.05, n = 3).[a]


400°C 500°C 400°C 500°C 400°C 500°C


DC(g kg‐1)

2.20±0.31

1.85±0.25

0.85±0.01

0.75±0.02

0.51±0.09

0.40±0.02

0.52±0.02

0.41±0.10

0.13±0.10

0.13±0.10

0.12±0.05

0.19±0.07 PC<PN<PL 500<400

DIC(g kg‐1)

0.39±0.04

0.44±0.04

0.57±0.03

0.54±0.03

0.32±0.03

0.31±0.03

0.38±0.03

0.37±0.04

0.014±0.003

0.025±0.003

0.034±0.005

0.055±0.012 PC<PN<PL 400<500

DOC(g kg‐1)

1.81±0.34

1.46±0.29

0.28±0.04

0.21±0.04

0.20±0.06

0.10±0.03

0.14±0.03

0.10±0.03

0.12±0.01

0.10±0.01

0.09±0.003

0.10±0.01 PC, PN<PL 500<400

NH4‐N(mg kg‐1)

8.5±0.39

6.69±0.69

11.3±6.41

3.49±0.15

2.86±0.27

1.94±0.01

2.12±0.12

2.28±0.44

1.75±0.29

7.93±6.16

2.41±0.16

2.37±0.08 PN<PL

NO3‐N(mg kg‐1)

<0.4 <0.4 <0.4 <0.4 1.02±0.01

1.07±0.02

1.27±0.06

1.11±0.02

<0.4 <0.4 <0.4 <0.4

[a] SA = steam activation; < indicates mean contains results below the detection limit.

lowest pH, which would support Tyron's hypothesis;however, the pH of PL biochar was similar to the PN biocharalthough it contained higher concentrations of total Ca, K,and Mg than PN biochar (table 2).

Higher CEC was associated with higher concentrations ofminerals in the feedstock. Mészáros et al. (2007)hypothesized that K, Mg, Na, and P in the biomass maycatalyze the formation of oxygen groups on the biocharsurface at low pyrolysis temperatures. Oxygen groups suchas carboxyls, lactones, and phenols could contribute to thepresence of negative surface charges (Boehm, 1994).

Dissolved C concentrations were very low (table 4).Feedstock had a significant effect on DC in the biocharleachate, with PC < PN < PL. Dissolved inorganic C was alsoaffected by feedstock, with PC < PN < PL. The PL biocharhad a higher proportion of DOC than PC or PN biochars. ThePL feedstock is a combination of wood chip (typically pine)bedding and poultry manure. The manure may contribute tohigher DOC leached from the PL biochar.

DOC plays an important role in many soil processes,including serving as an energy source for the microbialcommunity and reacting with other soil solution components(Sposito, 1989). Biochars are known to contain condensedvolatile compounds. These compounds are either lost to thegaseous or liquid phase or undergo further reactions to formsecondary char at high temperatures (Antal and Grønli,2003). Garcia‐Perez et al. (2007) identified water‐solublecompounds from pyrolysis of lignin materials to containmono‐ and oligo‐sugars, formic and aecetic acids, as well asmethanol, hydroxyl‐acetaaldehyde, and 1‐hydroxyl‐2‐propanone. Schnitzer et al. (2007) identified numerousorganic compounds in the light and heavy fractions of poultrylitter pyrolyzed at 330°C, including N-heterocyclics,substituted furans, phenol and substituted phenols, benzenesand substituted benzenes, as well as aliphatic C chains. It islikely that some of these compounds remain trapped in thebiochar pore structure, but few of these compounds appear tobe immediately water soluble.

Ammonium‐nitrogen in the biochar leachate was alsofound in very low concentrations (table 4). No NO3-N wasdetected in any of the leachates. The NH4-N concentrationswere highest in the leachate from the PL biochar. Freshpoultry litter typically contains about 2.8 g NH4-N kg-1

(University of Georgia Agricultural and Environmental

Services Laboratory, unpublished data). Small amounts ofthis NH4-N may remain trapped, or microbes may havemineralized nitrogen‐containing organic compounds in thebiochar. Das et al. (2008) found that the liquid productsobtained from poultry litter pyrolysis enhanced microbialgrowth in well water and concluded that N-heterocycliccompounds derived from proteins were responsible for thatincrease. A small fraction of these compounds may bepresent in the biochars.

INFLUENCE OF PYROLYSIS TEMPERATURE

The average conversion ratio (biochar weight / feedstockweight) was 33.2%. Biochar yield decreased with increasedpyrolysis temperature, and except for N, nutrientconcentrations were higher in the biochar produced at 500°C(tables 2a and�b). Due to the wide range of initial nutrientconcentrations in the feedstock, there were significantinteractions between feedstock and temperature for total N,P, Mg, Mn, Cu, Fe, Zn, and Al (p < 0.05).

As noted earlier, N was conserved in the biochar (fig. 1b).After forest fires, on average, only 3% of the N in the biomassis found in ash, which contains black carbon or biochar(Giardina et al., 2000). Almendros et al. (2003) found C andN enrichment in charred residues during thermaltransformation of peat organic matter. Nitrogen wasincorporated into structures resistant to heating at moderatethermal oxidation by aromatization and formation ofheterocyclic N (Almendros et al., 2003). Studies of wildfireeffects on biomass composition indicate that N begins tovolatilize at 200°C, and above 500°C half of the N in organicmatter is lost to the atmosphere. Our study indicated that arelatively high proportion of the feedstock N was conservedat low pyrolysis temperatures, and as expected more N wasretained in the biochar at 400°C compared to 500°C (fig. 1b).

Knicker et al. (2005) has shown that fire and carbonizationcan increase the N content of SOC, but the alterations inchemical structure have long‐term consequences for Navailability (Knicker and Skjemstad, 2000). Field trials of PNand PC biochar as a soil amendment with corn (Zea mays)indicate that PN biochar N is not plant available (Gaskin et al.,2007). However, Tagoe et al. (2008) studied N recovery of15N‐labeled chicken manure and did not find differences in Navailability between carbonized and dried chicken manure.

2067Vol. 51(6): 2061-2069

Figure 2. Representative relationship of the ratio of nutrient (K) in thebiochar to feedstock and conversion efficiency for pine chip, peanut hull,and poultry litter biochars. Solid circles represent means, and barsindicate standard errors.

The total concentration of other elements (P, K, Ca, andMg) significantly increased with increasing volatizationlosses of C, H, O, and N (tables 2a and 2b). Potassium isrepresentative of the nutrient concentration seen (fig. 2).Potassium and P vaporize at temperatures above 760°C, Sand Na need temperatures above 800°C, and Mg and Ca arelost only at temperatures above 1107°C and 1240°C,respectively (Lide, 2004, reviewed by Knicker, 2007). Therewas a significant interaction between temperature andfeedstock for Mehlich I extractable concentrations of theseelements (p = 0.05). At the low nutrient concentrations seenin the PC biochar, temperature appeared to have little effect.In the PN and PL biochars, Mehlich I extractable nutrientstended to decrease with increasing temperature. Mehlich Iextractable Al and Fe were significantly increased in the500°C biochar (table 3b).

The CEC of biochar produced at 500°C was significantlyless than that produced at 400°C (table 2a, p < 0.01). Therewas a significant interaction between feedstock andtemperature. In general, the literature indicates the loss ofsurface functional groups with the increase in pyrolysistemperature. Guo and Rockstraw (2007b) showed that thenumber of acidic functional groups decreased withincreasing temperature. The highest decrease occurredbetween 300°C and 400°C, and the loss of these acidicgroups slowed after 400°C. This process may havecontributed to the lower CEC seen at higher temperatures.Iyobe et al. (2004) indicated that lignin and cellulose undergothermolysis at 400°C to 500°C, which creates acidicfunctional groups such as carboxyls and phenolic hydroxyls.Chun et al. (2004) found decreasing acidity and increasingbasicity with increasing pyrolysis temperature.

Temperature influenced DC (table 4). The higher temper-ature reduced the concentration of organic C but increasedinorganic C significantly.

INFLUENCE OF STEAM ACTIVATION

Steam activation had little effect on the studiedparameters (tables 2a, 2b, 3a, 3b, and 4). Productiontechnology is known to influence physical parameters, andsteam can improve the yield and surface characteristics atelevated pressures and temperatures (Antal and Grønli,2003). At the relatively low pyrolysis temperatures used inthis study, we only found significantly higher C and MehlichI extractable B concentrations in steam‐activated biochar(p�< 0.05).

CONCLUSIONSPyrolytic biochar has the potential to be used in

agricultural production to sequester carbon and serve as afertilizer. Although pyrolysis conditions are known to affectthe chemical and physical characteristics of biochar, at therelatively low pyrolysis temperatures used in this study,feedstock characteristics had the greatest influence on keyagricultural characteristics. Carbon concentrations in thebiochars decreased with increasing mineral content of thefeedstock. Little DC was leachable from the fresh biochar. Ahigh proportion of the feedstock N was conserved in thebiochar; however, the N may not be plant available. Nutrientssuch as P, K, and Ca are extractable with a weak double acidextractant and may be plant available.

The higher pyrolysis temperature increased nutrientconcentrations, except for N, but decreased CEC. Recentliterature has shown that natural long‐term oxidation ofbiochar in the soil increases the amount of negative chargeson the biochar surface (Cheng et al., 2008). Development andoptimization of pyrolysis and post‐production treatments toincrease CEC or available nutrients is important in order toincrease the immediate benefits of biochar applications inagriculture.

ACKNOWLEDGEMENTS

This work was conducted with funding from the State ofGeorgia and the U.S. Department of Energy. We wish tothank Dr. Jim Kastner for his helpful comments on variousideas in the manuscript, and Mr. Roger Hilten for assistancewith this project.


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Glaser, B., E. Balashov, L. Haumaier, G. Guggenberger, and W.Zech. 2000. Black carbon in density fractions of anthropogenicsoils of the Brazilian Amazon region. Org. Geochem. 31(7‐8):669‐678.

Guo, Y., and A. D. Rockstraw. 2007a. Physicochemical propertiesof carbons prepared from pecan shell by phosphoric acidactivation. Bioresource Tech. 98(8): 1513‐1521.

Guo, Y., and D. A. Rockstraw. 2007b. Activated carbons preparedfrom rice hull by one‐step phosphoric acid activation.Microporous Mesoporous Mat. 100: 12‐19.

Ioannidou, O., and A. Zabaniotou. 2007. Agricultural residues asprecursors for activated carbon production: A review. Renew.Sust. Energy Rev. 11(9): 1966‐2005.

Iyobe, T., T. Asada, K. Kawata, and K. Oikawa. 2004. Comparisonof removal efficiencies for ammonia and amine gases betweenwoody charcoal and activated carbon. J. Health Sci. 50(2):148‐153.

Knicker, H. 2007. How does fire affect the nature and stability ofsoil organic nitrogen and carbon? A review. Biogeochem. 85(1):91‐118.

Knicker, H., and J. O. Skjemstad. 2000. Nature of organic carbonand nitrogen in physically protected organic matter of someAustralian soils as revealed by solid‐state 13C and 15N NMRspectroscopy. Australian J. Soil Res. 38(1): 113‐127.

Knicker, H., F. J. Conzález‐Vila, O. Polvillo, J. A. González, and G.Almendros. 2005. Fire‐induced transformation of C- and N-forms in different organic soil fractions from a dystric cambisolunder a Mediterranean pine forest (Pinus pinaster). Soil Biol.Biochem. 37(4): 701‐718.

Kuo, S. 1996. Phosphorus: Part 3. Chemical methods. In Methodsof Soil Analysis, 869‐919. Madison, Wisc.: SSSA and ASA.

Lal, R. 2004. Soil carbon sequestration impacts on global climatechange and food security. Science 304(5677): 1623‐1627.

Lehmann, J., J. P. da Silva Jr., C. Steiner, T. Nehls, W. Zech, and B.Glaser. 2003. Nutrient availability and leaching in an archaeologicalanthrosol and a ferralsol of the central Amazon basin: Fertilizer,manure and charcoal amendments. Plant Soil 249(2): 343‐357.

Lehmann, J., J. Gaunt, and M. Rondon. 2006. Bio‐charsequestration in terrestrial ecosystems: A review. Mit. Adapt.Strat. Global Change 11(2): 403‐427.

Liang, B., J. Lehmann, D. Solomon, J. Kinyangi, J. Grossman, B.O'Neill, J. O. Skjemstad, J. Thies, F. J. Luizão, J. Petersen, andE. G. Neves. 2006. Black carbon increases cation exchangecapacity in soils. SSSA J. 70(5): 1719‐1730.

Mehlich, A. 1953. Determination of P, Ca, Mg, K, Na, and NH4.Mimeo 1953. Raleigh, N.C.: North Carolina Department ofAgriculture, North Carolina Soil Test Division.

Mészáros, E., E. Jakab, G. Varhegyi, J. Bourke, M. Manly‐Harris, T.Nunoura, and M. J. Antal. 2007. Do all carbonized charcoalshave the same chemical structure? 1. Implications ofthermogravimetry: Mass spectrometry measurements. Ind. Eng.Chem. Res. 46(18): 5943‐5953.

Pietikäinen, J., O. Kiikkilä, and H. Fritze. 2000. Charcoal as ahabitat for microbes and its effect on the microbial communityof the underlying humus. Oikos 89(2): 231‐242.

Schmitdt, M. W. I., J. O. Skjemstad, E. Gehrt, and I.Kögel‐Knabner. 1999. Charred organic carbon in Germanchernozemic soils. European J. Soil Sci. 50(2): 351‐365.

Schnitzer, M. I., C. Monreal, G. Jandl, P. Leinweber, and P. B.Fransham. 2007. The conversion of chicken manure to biooil byfast pyrolysis: II. Analysis of chicken manure, biooils, and charby curie‐point pyrolysis‐gas chromatography/mass spectrometry.J. Environ. Sci. Health B 42(1): 79‐95.

Seiler, W., and P. J. Crutzen. 1980. Estimates of gross and net fluxesof carbon between the biosphere and the atmosphere frombiomass burning. Climatic Change 2(3): 207‐247.

Speir, R. A. 2008. Use of pyrolysis char in southeastern soils. MSthesis. Athens, Ga.: University of Georgia, Warnell School ofForestry and Natural Resources.

Sposito, G. 1989. The Chemistry of Soils. New York, N.Y.: OxfordUniversity Press.

Steiner, C. 2007. Slash and char as alternative to slash and burn:Soil charcoal amendments maintain soil fertility and establish acarbon sink. PhD diss. Bayreuth, Germany, University ofBayreuth, Faculty of Biology, Chemistry and Geosciences.

Steiner, C., W. G. Teixeira, J. Lehmann, T. Nehls, J. L. V. d.Macêdo, W. E. H. Blum, and W. Zech. 2007. Long‐term effectsof manure, charcoal, and mineral fertilization on crop productionand fertility on a highly weathered central Amazonian uplandsoil. Plant Soil 291(1‐2): 275‐290.

Steiner, C., K. C. Das, M. Garcia, B. Förster, and W. Zech. 2008a.Charcoal and smoke extract stimulate the soil microbialcommunity in a highly weathered xanthic ferralsol.Pedobiologia 51(5‐6): 359‐366.

Steiner, C., B. Glaser, W. G. Teixeira, J. Lehmann, W. E. H. Blum,and W. Zech. 2008b. Nitrogen retention and plant uptake on ahighly weathered central Amazonian ferralsol amended withcompost and charcoal. J. Plant Nutrition Soil Sci. (in press).

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Chapter _ CHARACTERIZATION OF CHAR FOR AGRICULTURAL USE IN THE SOILS OF THE SOUTHEASTERN UNITED STATES J. GASKIN, K. DAS, A. TASISTRO, L. SONON, K. HARRIS, B. HAWKINS Dept. of Biological and Agricultural Engineering and Soil, Plant and Water Laboratory, University of Georgia, and EPRIDA., Athens, Georgia, US Abstract: Char produced from the pyrolysis of biomass has potential as an agricultural amendment for increasing agricultural productivity in the

infertile, low C soils of the southeastern United States, but it is unclear if the chars produced by pyrolysis plants will function in soils similar to the charcoal in Terra Preta. Recent work in characterizing pyrolysis char indicates that the feedstock, temperature, and carrier gas has a strong influence on important characteristics for agricultural production, such as available nutrients, cation exchange capacity, and mineralization rates. Preliminary data indicate pyrolysis char may increase CEC, sorbs P, and serves as a source of plant available K. Nitrogen mineralization data and first growing season field trials with corn (Zea mays) indicate although some mineralization may occur, N in high N char (2%) is not readily available. A better understanding of char effects on soil processes is needed.

Keywords: char, Ultisols, agricultural amendment, nutrients, nitrogen, mineralization, cation exchange capacity, phosphorus sorption

1. INTRODUCTION Char produced from the pyrolysis of biomass has potential as an agricultural amendment in low fertility soils. Much

of the interest in its potential use as an agricultural amendment has been stimulated by research discussed in this book and the previous volumes on the role of charcoal in Terra Preta soils. Results from studies conducted in South American and African tropics on acidic, highly-weathered Oxisols with low organic carbon, cation exchange capacity, and base saturation indicates that addition of charcoal has significantly influenced nutrient cycling, soil biology, and crop productivity (Glaser et al. 2002; Lehmann and Rondon 2006; Oguntunde et al. 2004). Increased yields and biomass have been reported for various legumes (Iswaran et al. 1980; Lehman et al. 2003; Topoliantz et al. 2005) and for corn (Lehmann and Rondon 2006; Oguntunde et al. 2004). Increased productivity may be related to available nutrients (Glaser et al. 2002; Lehman et al. 2003; Steiner et al. 2007), or increases in pH (Topoliantz et al. 2005; Steiner et al. 2007), and cation exchange capacity (CEC)(Steiner et al. 2007, Liang et al. 2006), as well as changes in water relations and soil biology (Glaser et al. 2002; Steiner et al. 2004). Although most studies report increased plant productivity with charcoal addition, plant biomass decreases have been observed, particularly at high application rates (Glaser et al. 2002). These responses could be related to nitrogen immobilization through high C:N ratios and sorption of NH4-N and NO3-N(Lehmann and Rondon 2006).

The southeastern United States is an important agricultural area. The state of Georgia alone has approximately 4.3 million hectares of corn (Zea mays), soybean (Glycine max), cotton (Gossypium hirsutum), and peanuts (Arachis hypogaea) in production and 9.6 million hectares of forestland largely in loblolly pine (Pinus taeda) production (USDA 2002; Georgia Forestry Association 2007). The growing interest in biofuels is increasing demands on row crop production and may also increase demand on forestlands. The Ultisols of the southeastern United States are similar to tropical Oxisols with low organic carbon contents of less than 1%, low cation exchange capacities of approximately 5 cmol kg-1, and low base saturation of usually less than 30% (Perkins 1987). Char produced as a byproduct of energy production through pyrolysis may provide an opportunity to increase the productivity of southeastern soils, similar to the way charcoal functions in Terra Preta. However, because char characteristics vary with feedstock and pyrolysis conditions (Harris et al. 2006; Antal and Gronli 2003), a better understanding of the influence of these factors on char characterisitics and the effect of different chars on soil processes in the southeastern United States is needed.

2. PYROLYSIS CONDITIONS AND CHAR CHARACTERISTICS

Char or charcoal corresponds to black carbons that result from the incomplete combustion of biomass. Black carbon consists of graphite-like planes (graphene layers) that show varying degrees of disorientation. The resulting spaces between these planes constitute porosity. The capacity of char to remove impurities from solutions and gases has been known for many centuries. This is due to the porous nature of the material (Barkauskas 2002) and to the surface chemical properties including the type and number of functional groups (Stoeckli et al. 2004). Charcoal has chemical reactivity due to the existence of unsaturated valence (active sites) at the edges of the aromatic planes. The ratio of these active sites in relation to the inert carbon atoms within

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the graphene layers increases as the surface area increases. Heteroatoms, such as oxygen, hydrogen or nitrogen also have a strong influence on the mechanisms of the adsorption process. Oxygen is the most important heteroatom and is part of chemical groups that have both Lewis base properties such as chromene and pyrone or acidic properties such as anhydrides, lactones, lactols, phenols, carbonyls, and carboxyls. The presence and quantity of these groups affect the capacity of char to add to the cation or anion exchange capacity of the soil and other soil productivity properties. Charcoals are known to sorb cations (Lima and Marshall 2005a) and also anions when basic surface oxides are present due to exposure to the atmosphere (Boehm, 1994). These sorption capacities may create the potential for char to retain needed nutrients in the low exchange capacity soils of the southeastern United States. 2.1 Feedstocks

The mineral content of the char depends upon the nature of the feedstock and can influence the surface chemistry of charcoal by interaction with electrons of the aromatic rings and through electron paramagnetism. (Benaddi et al. 2000). Ash complicates interpretation of surface phenomena of carbon. Ash solubility in water is variable, making the analysis of surface groups difficult at higher ash concentrations. Insoluble metal oxides involved in the charge development on the carbon surface become charged in aqueous suspension, and are considered part of the active surface sites.

Feedstock particle size also affects char yield from pyrolysis. At low pyrolysis temperature, larger particle sizes favor longer inter-pore residence time for volatiles increasing yield (Antal and Gronli, 2003).

2.2 Pyrolysis Conditions Important parameters that determine quality and yield of the carbonized product are the rate of heating, final temperature, and the gas environment (Bansal et al., 1988). A low heating rate during pyrolysis leads to lower volatilization and higher char yields. This creates char with higher carbon contents but does not affect char microporosity. In addition, chars developed at low heating rates are heavier and denser than those from high heating rates. This may be an advantage for agricultural use in terms of handling properties. The final temperature during pyrolysis typically ranges between 400 and 600 oC, and does not exceed 800 oC. Guo and Rockstraw (2007) observed that surface area and porosity did not develop at temperatures < 300 oC and that from 300 oC onwards, the concentration of acidic surface groups decreased with increasing temperature. The decrease occurred more quickly between 300 and 400 oC, and slowed after 400 oC, probably due to an equilibrium between decomposition and formation of strong acidic surface groups, or because most of the temperature-sensitive strong acidic groups had disappeared. Iyobe, et al. (2004) reported that thermolysis of cellulose or lignin occurred actively at 400 to 500 oC, with the formation of acidic functional groups, such as carboxyls and phenolic hydroxyls. The amount of acidic functional groups continue to decrease with pyrolysis temperatures > 600 oC. Hydroxide (C-OH), C=O, and C-H groups are largely lost at temperatures > 650°C, and most of the aromatic and C-H groups are decomposed above 750°C (Antal and Gronli, 2003). Above 950°C chars are almost like graphite with little active chemistry on its surfaces. The effect is decreasing ability to sorb cations. Asada et al. (2002) reported that char obtained by carbonizing bamboo at 500 oC had the highest removal effect for NH3 compared to carbonizing at 700 or 1000oC. In general, these data indicates chars produced at lower temperatures (<500 oC) may hold the greatest promise for agricultural use in terms of nutrient holding capacity. The gas environment during pyrolysis also exerts considerable influence on char properties. Lower carrier gas flow rates result in longer residence time of vapors in the char matrix, which allows for char-catalyzed secondary reactions to occur. Steam may increase the presence of oxygen in surface functional groups. Carbon-oxygen surface compounds are by far the most important in influencing surface reactions, surface behavior, hydrophilicity, and electrical and catalytic properties of carbons. Substantial quantities of oxygen can be introduced in the course of charcoal production by an oxidating gas such as steam (Strelko et al. 2002). 2.3 Comparison between traditional two-step pyrolysis and activation with 1-step steam pyrolysis Typically chars produced at temperatures around 400 to 600 oC do not have the well developed surface areas or adsorbent properties of activated carbons because of tars deposited on the solid surface that restrict pore structures. Steam activation at temperatures between 800 and 1,100 oC physically removes these residues and opens pores. After activation, chars have higher surface area, adsorption capacity and pore size distribution (Gregova et al. 1994; Alaya et al. 2000). The combination of this two-step process into a single step, which involves pyrolyzing under steam conditions, may increase surface area and increase adsorbent properties, and requires less energy and less time. Steam pyrolysis at low temperatures (600 oC) has been shown to increase micropores with the ratio of micropore volume to total pore volume approaching 95% (Alaya et al. 2000). These authors suggest that steam enhances the evolution of volatile molecules at

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lower temperatures and prevents the cracking of volatiles. In addition, gasification (conversion of solids to gases) is induced much earlier (600 oC compared to 800 to 900 oC in non-steam environments) and results a more porous carbon skeleton. Chars produced at lower temperatures with steam may have a more active surface chemistry; however, the literature is not clear about the impacts of one-step processing on nutrient properties and surface chemistry. Based on available literature on char and activated carbons, it appears that chars produced at low pyrolysis temperatures with steam may hold the greatest promise for agricultural use due to lower production cost, higher surface functional groups for sorption, and a more dense char product.

3. AGRICULTURAL CHARACTERISTICS OF PYROLYSIS CHAR 3.1 Feedstock and Pyrolysis Condition Effects on Nutrient Status Analyses of char from common feedstocks in the Southeastern US confirm the effect of feedstock and temperature on char composition. Total nutrients were analyzed in chars produced from peanut hull (PN), pine chip (PC), and hardwood (HW) feedstocks pyrolyzed at low temperatures (380, 400, and 420 oC) with steam in a small furnace, and poultry litter (PL) at 400 oC in a batch reactor in a steam flow environment (Table 1). At these lower pyrolysis temperatures, the initial nutrient content of the feedstock had a larger effect on char nutrient concentration than pyrolysis temperature (Table 1, Figure 1). Small increases in pyrolysis temperature increased the total nutrient concentration in the char of most nutrients (e.g. K, Figure 1). Table 1. Total carbon and nutrient concentrations for feedstocks and chars (on an as is basis) produced from those feedstocks at 400 oC with steam.

Constituent Peanut hull Feedstock Char

Poultry Litter Feedstock* Char

Pine chips Feedstock Char

Hardwood Feedstock Char

C (%) 47.7 65.5 N/A 41.7 46.5 67.0 44.7 70.3 N (%) 1.44 2.00 3.80 3.70 0.05 0.14 0.20 0.30 C:N 33 33 N/A 11 949 543 224 234 S (%) 0.13 0.13 0.42 1.18 0.02 0.02 0.02 0.02 P mg kg -1 732 1,620 11,930 33,580 30.0 235 92.9 278 K mg kg -1 6,340 15,372 19,339 45,593 436 1,973 937 2,409 Ca mg kg -1 1,880 4,420 17,900 46,760 418 1,686 794 2,709 * Average Georgia poultry litter concentrations analyzed by the University of Georgia Agricultural and Environmental Services Laboratory N/A – not available

0

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Figure 1. Total nutrients in char produced from pine chips (PC), hardwoods (HW), and peanut hulls (PN) pyrolized with steam at three different temperatures. At these low pyrolysis temperatures, the total N concentration in the char was similar to that of the initial feedstock (Table 1). Total N concentration in the PL and PN char was high at 3.7% and 2%, respectively. The PL char concentration was higher than that reported for active carbon produced from turkey litter (1.12%) although the N concentration of the turkey litter feedstock was similar at 3.84%(Lima and Marshall 2005b). The turkey litter active carbon was produced at 700 oC and activated with steam at 800 oC, which may have volatilized more N. The N concentrations in PC and HW char were similar to those reported for pinewood (0.11%) and oak board (0.18%) char by Antal and Gronli (2003).

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Although the N concnetration of the PN char is potentially high enough to offer a substantial nitrogen input and the C:N ratio is relatively low (33, Table 1), the N does not appear to be readily available. Nitrogen mineralization was very low in incubations (24-days at 25 o C, 55% water filled pore space) of infertile, low C Tifton soils (fine-loamy, siliceous, thermic Plinthic Kandiudults) amended with PN and PC chars at 11 and 22 Mg ha-1 equivalent rate (Table 2). These PN and PC chars were produced in a pilot scale pyrolysis unit at 400 oC with steam. Peanut hull char C and N concentrations were 72.85and 1.90%, respectively, and PC char C and N were 76.99 and 0.17%, respectively. There was no statistical difference in NH4-N concentrations between the control and char amended soils (p=0.05). There was a trend for higher NO3-N concentrations in the PN amended soils, but only the PN 11 Mg ha-1 rate was statistically different from the control. Table 2. Mean change (final –initial) in ammonium- and nitrate-nitrogen concentrations with standard deviations in Tifton soils amended with peanut hull (PN) and pine chip (PC) char at 11 and 22 Mg ha –1 and incubated for 24 days. Analysis of variance with mean separation by Tukey-Kramer Multiple Comparison test. Letters within the same column indicate statistical difference at the p=0.05 level.

Feedstock n Δ NH4-N Δ NO3-N

---------------mg kg-1-------------- PN 11 4 1.49 +/- 0.24 5.53 +/- 0.65b PN 22 4 0.94 +/- 0.78 5.08 +/- 0.62a PC 11 4 1.19 +/- 0.36 3.62 +/- 0.51a PC 22 4 1.44 +/- 0.26 4.41 +/- 0.16a

Control 4 1.37 +/- 0.38 3.26 +/- 1.66 We saw similar indications that N in the high N char was not plant available in the first year of field trials on similar Tifton soils with irrigated corn (Zea mays, Gaskin et al. 2006). Peanut hull char was incorporated to a depth of 15 cm in microplots (1.8 x 2.2 m) at rates of 0, 11 and 22 Mg ha-1 in a factorial combination with two rates of nitrogen fertilizer (0 and 213 kg N ha-1) surface applied as ammonium nitrate. Tissue samples at the earleaf stage during the first growing season only showed a significant effect (p=<0.0001) due to N fertilizer. The mean N tissue concentration in the PN char/no N fertilizer treatments were similar to the control (1.40%) and had average N concentrations averaging 1.13% for the PN 11 and 1.52% for the PN 22 treatment. Nitrogen tissue concentrations in the N fertilized treatments averaged 2.91%. At the p=0.05 level, there was a significant effect due to N fertilizer for both grain yield and stover (p= <0.0001; Figure 2), but no significant effect due to char rate for grain (p=0.7197). There was a significant effect of char rate for stover (p=0.0241). The interaction between char and fertilizer was only significant for the stover (p=0.0145). These preliminary data indicate, although some N may be mineralizing, the N in the PN char is not readily available to microorganisms in the short–term (24-days) and is not highly plant available over a growing season (approximately 4 months).

Grain Stover

02468

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er

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FPN22

PN11

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Figure 2. Corn grain yield and stover (dry wt basis) from Tifton soil plots amended with peanut hull (PN) biochar. Fertilizer – N fertilizer check,

PN22+F- PN char at 22 Mg ha-1 + N fertilizer, PN11+F- PN char at 11 Mg ha-1 + N fertilizer, PN22- PN char at 22 Mg ha-1, PN11 char at 11 Mg ha-1, Control- no amendment or N fertilizer.

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Although N in the char does not appear to be readily available, the char may serve as a source for other nutrients, particularly K. Mehlich I K at the end of the first growing season was higher in the PN char amended plots than the control (Table 3). Table 3. Mehlich I K in Tifton soil amended with peanut hull (PN) char at 11 and 22 Mg ha-1. Analysis of variance with mean separation by Tukey-Kramer Mulitple Comparision Test. Letters within rows indicate statistical difference at p=0.05 level.

Depth Control Fertilizer PN 11 PN 11 + F PN 22 PN 22 + F

cm --------------------------------------------------- mg kg-1 ---------------------------------------------------------

0-15 28.3 +/- 8.7a 33.2 +/- 12.6a 53.2 +/- 6.8b 49.2 +/- 9.9b 74.1 +/- 11.0c 65.9 +/- 14.3c 15-30 21.3 +/- 4.4a 24.0 +/- 8.4a 43.2 +/- 4.1b 38.4 +/- 7.4b 68.2 +/- 11.3c 51.0 +/- 7.0c

3.2 Feedstock and Pyrolysis Condition Effects on Cation Exchange Capacity The PN, PC, and HW chars (Table 1) were analyzed for cation exchange capacity (CEC) using a modified Na-acetate /ethanol/NH4-acetate compulsory replacement method (Sumner and Miller 1996) with sodium analyzed by atomic absorption spectrophometry. Due to interference of the char ash, chars were leached with deionized water before analysis to remove soluble salts. In this preliminary study, there was a trend for higher CEC at 400 oC (Table 4). The PN char had the highest CEC perhaps due to its higher initial mineral concentrations. Table 4. Mean cation exchange capacity and standard deviation in peanut hull(PN), pine chip (PC) and hardwood (HW) chars produced at three pyrolysis temperatures with steam.

Temperature

Feedstock 380° C 400° C 420° C ---------------------------------cmol kg-1------------------------------------

PN 36.7+/-0.76 (n=4) 44.0+/-0.35 (n=2) 28.0+/-5.26 (n=4) PC 18.6+/-1.34 (n=3) 27.0+/-0.60 (n=2) 16.5+/-2.42 (n=4) HW 22.6+/-0.04 (n=2) 22.9+/-3.21 (n=2) 14.1+/-0.34 (n=2)

3.3 Feedstock and Pyrolysis Condition Effects on Sorption Properties Subsamples of the PC and PN chars (Table 1) pyrolyzed at 420oC were ground to <420 µm and washed with deionized water to remove soluble salts and air-dried. Chars were then added to Tifton soils at the rate of 0.05 g char g-1 soil and phosphorus sorption isotherms were determined using batch techniques. Soil-char mixtures were equilibrated with five concentrations of P (0, 5, 20, 50, and 100 mg P L-1) in 0.01M CaCl2 matrix. The capacity and intensity of sorption by soil varied with the type of char added to soil. The amount of P sorbed was highest in soil amended with PN char, while the lowest P sorption occurred in unamended soil (Figure 3). All systems showed a sharp increase in adsorption at low equilibrium P concentrations but sorption eventually reached a plateau. This is a characteristic of an L-curve isotherm where the adsorbate (P) has high affinity for the sorption sites but sorption diminishes regardless of the amount of adsorbate as surface area decreases (Sposito 1989). Such a relationship suggests a strong interaction between the P and the exchange surfaces and that the overall sorption was dependent on the properties of both components (Giles et al. 1960; McBride 1994).

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Figure 3. Phosphorus adsorption isotherm form a Tifton soil amended with pine chips (PC), and peanut hull (PN) chars pyrolyzed at 420 oC with steam at 0.05 g char g-1 soil . 4. SUMMARY Soils in the southeastern United States are typically have low C, CEC, and base saturation. Studies of Terra Preta soils show charcoal has an important influence on these soils productivity and reviews of the activated carbon literature illuminate some of the physical and chemical mechanisms that could influence soil productivity with char addition. Pyrolysis chars may have the potential to supply nutrients, sorb cations and anions. The literature and our data indicate pyrolysis conditions and the feedstock have considerable effects on char characteristics. Our studies on feedstocks commonly available in the southeastern United States indicate had CECs that potentially increase the ability of low C loamy sands to retain nutrients. Some chars also have the potential to increase P sorption. It is unknown at this point if there would be subsequent desorption of P by char and what affect this may have on crops. Preliminary studies indicate that N from chars with a relatively high N content such as peanut hulls was not readily bioavailable during the first year of cropping, but some chars contain mineral nutrients such as K that are available to crops. Our preliminary work indicates char addition may have potential agricultural benefits, but a better understanding of how char from various feedstocks and produced under different pyrolysis conditions changes soil processes and crop response is needed. 5. REFERENCES Alaya, M.N., B.S. Girgi, and W.E. Mourad. (2000). Activated carbon from some agricultural wastes under action of one-

step steam pyrolysis. Journal of Porous Materials 7: 509-517. Antal, M.J. and M. Gronli. (2003). The art, science, and technology of charcoal production. Industrial and Engineering

Chemistry Research 42:1619-1640. Asada, T., Ishihara, S., Yamame, T., Toba, A., Yamada, A., and Oikawa, K. 2002. Science of bamboo charcoal: study on

carbonizing temperature of bamboo charcoal and removal capability of harmful gases. Journal of Health Science 48[6], 473-479.

Bansal, R.C., J. Donnet, F. Stoeckli. 1988. Active Carbon. Marcel Dekker, Inc. New York. 482 pp. Barkauskas, J. (2002). Functional groups on the surface of activated carbons. Part A. Investigation by means of proton

affinity distribution. Chemine Technologia, 24 (3). Benaddi, H., T. J. Bandosz, J. Jagiello, J. A. Schwarz, J. N. Rouzaud, D. Legras, and F. Beguin. 2000. Surface

functionality and porosity of activated carbons obtained from chemical activation of wood. Carbon 38(5):669-674. Boehm, H.P. (1994). Some aspects of the surface chemistry of carbon balcks and other carbons. Carbon, 32 (5), pp. 759-

769. Gaskin, J., L. Morris, D. Lee, R. Adolphson, K. Harris, and K.C. Das. (2006). Effect of pyrolysis char on corn growth and

loamy sand soil characteristics. Abstracts of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America International Annual Meetings. Nov. 12-16, 2006. Indianapolis, IN.

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Georgia Forestry Commission. (2007). Georgia Facts. http://www.gfagrow.org/facts.asp Giles, C.H., MacEwan, T.H., Nakhwa, S.N., and Smith, D. 1960. Studies in adsorption. isotherms and its use in

diagnosis of adsorption mechanisms and in measurements of specific surface areas of solids. J. Chem. Soc., London, 3973-3993.

Glaser, B., J. Lehmann, and W. Zech. (2002). Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review. Biology and Fertility of Soils 35:219-230

Gregova, K., N. Petrov, and S. Eser. (1994). Adsorption properties and microstructure of activate carbons produced from agricultural by-products by steam pyrolysis. Carbon 32(4):693-702.

Guo, Y. and D. A. Rockstraw. 2007. Physicochemical properties of carbons prepared from pecan shell by phosphoric acid activation. Bioresource Technology, 98 (8), 1513-1521

Harris, K., J.W. Gaskin, L.S. Sonon, and K.C. Das. (2006). Characterization of pyrolysis char for use as an agricultural soil amendment. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America International Annual Meetings. Nov. 12-16, 2006. Indianapolis, IN.

Iswaran, V., K.S. Jauhri, and A. Sen. (1980). Effect of charcoal, coal and peat on the yield of moong, soybean and pea. Soil Biol. Biochem. 12:191-192.

Iyobe, T., T. Asada, K. Kawata, and K. Oikawa. (2004). Comparison of removal efficiencies for ammonia and amine gases between woody charcoal and activated carbon. Journal of Health Science 50[2], 148-153.

Liang, B., J. Lehman, D. Solomon, J. Kinyangi, J. Grossman, B. O’Neill, J.O. Skjemstad, J. Thies, F.J. Luizao, J. Peterson, and E.G. Neves. (2006). Balck carbon increases cation exchange capacity on soils. Soil Sci. Soc. Am. J. 70:1719-1730.

Lehman, J. and M. Rondon. (2006). Bio-char soil management on highly weathered soils in the humid tropics. In: Uphoff, N., A.S. Ball, E. Fernandes, H. Herren, O.Husson, M.Lang, C. Palm, J. Pretty, P. Sanchez, N. Sanginga, and J. Theis (eds). Biological Approaches to Sustainable Soil Systems. CRC Taylor and Francis, Boca Raton, FL.

Lehman, J. J. Pereira da Silva, Jr., C. Steiner, T. Nehls, W. Zech, and B Glaser. (2003). Nutrient availability and leachng in an archealogical Ahtrosol and a Ferrasol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant and Soil 249:343-357.

Lima, I. and W.E. Marshall. 2005a. Adsorption of selected environmentally important metals by poultry manure-based granular activated carbons. Journal of Chem Technol Biotechnol 80:1054-1061.

Lima, I and W.E. Marshall. 2005. Utilization of turkey manure as granular activated carbon: physical, chemical and adsorptive properties. Waste Management 25:726-732.

McBride, M.B. 1994. Environmental Chemistry of Soils. Oxford University Press, 406 pp. Oguntunde, P.G., M. Fosu, A.E. Ajayi, N. van de Giesen. (2004) Effects of charcoal production on maize yields, chemical

properties and texture of soil. Biol. Fertil. Soils 39:295-299. Perkins, H.,F. (1987). Characterization Data for Selected Georgia Soils. The Georgia Agricultural Experiments Stations,

College of Agriculture, The University of Georgia. Athens, GA. Special Publication 43. Sonon, L. K. Harris, J. Gaskin, and K Das. (2006). Phosphorus sorption characteristics of Tifton soil amended with

pyrolysis-derived chars. Abstracts of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America International Annual Meetings. Nov. 12-16, 2006. Indianapolis, IN.

Sposito, G. (1989). The Chemistry of Soils. Oxford University Press. NY, USA. Stoeckli, F., A. Guillot, and A.M. Slasli. (2004). Specific and non-specific interactions between ammonia and activated

carbons. Carbon 42 (8-9): 1619-1624. Strelko, V., D.J. Malik, and M. Streat. (2002). Characterisation of the surface of oxidized carbon adsorbents. Carbon

40(1):95-104. Steiner, C., W.G. Teixeira, J. Lehman, T. Nehls, J.L. Vasconcelos de Macedo, W. E. H. Blum, W. Zech. (2007). Lang

term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil. Plant Soil 291(1-2):275-290.

Steiner, C. W.G. Teixeira, J. Lehman, and W. Zech. (2004). Microbial response to charcoal amendments of highly weathered soils and Amazonian dark earths in Central Amazonia – Preliminary results. In: B. Glaser and W.I. Woods (eds). Amazonian Dark Earths: Explorations in Space and Time. Springer-Verlag, New York, NY. pp. 195-212.

Sumner, M.E. and W.P. Miller. (1996). Cation exchange capacity and exchange coefficients. In: Methods of Soil Analysis. Part 3. Chemical Methods. Soil Sci. Soc. Am. and Am. Soc. Agron. SSSA Book Series No. 5.

Topoliantz, S., J-F. Ponge, and S. Ballof. (2005). Manioc peel and charcoal: a potential organic amendment for sustainable soil fertility in the tropics. Biol. Fertil. Soils 41:15-21.

USDA. (2002). Census of Agriculture. 29 May 2007. <http://www.nass.gov/Data_and_Statistics/Quick_Stats/>

Danny M. Day, Eprida, Inc., 6300 Powers Ferry, Suite 307, Atlanta, Georgiadanny.day AT eprida.com, 404-228-8687Robert J. Evans, National Renewable Energy Laboratory, Golden, CoJames W. Lee, Oak Ridge National Laboratory, Oak Ridge, TN

Introduction and Abstract

Carbon dioxide (CO2) emissions from fossil fuel combustion directly contribute to ris ing atmospheric CO2 levels, which in turn are likely linked to global climate change. The need for efficient and economical technologies to rapidly sequester point source production of carbon dioxide has become both an urgent and widespread technical need. The significant adoption of any mitigation technology requires a measurable return to end-users. An example is coupling enhanced oil recovery (EOR) with deep well injection of CO2, though to be economically viable, the carbon dioxide source must be co-located with the oil fields. We propose an integrated sequestration approach in which agricultural waste products are used to produce hydrogen, a renewable fuel, and a carbon sequestering soil amendment (char) as a valuable co-product. The dual function char,derivitized with ammonium bicarbonate (2NH4HCO3) (“ABC”) obtained from treating power plant CO2 emissions, acts both as an enriched carbon, organic slow release fertilizer and a long-lived carbon storage medium in soils or ECOSS™.

This project had the following objectives:

?To verify a hydrogen co-product could be produced that would offer sufficient value for high volume application

?Test a simply production process that would allow the co-product to be produced from the exhaust of fossil fuel combustion,

?Analyze the material for characteristics needed of a large volume co-product.

The ammonium bicarbonate technology, developed through the collaboration of Oak Ridge National Laboratory (ORNL), the National Renewable Energy Laboratory (NREL) and Eprida Scientific Carbons, Inc. (E-SCI), operates at ambient temperature and pressure and does not require carbon dioxide separation or energy intensive compression. Chars generated from agricultural waste pyrolysis have been derivitized with the ammonium bicarbonate. This research provides results that point toward the utilization as a time-release fertilizer while concurrently sequestering stable charcoal in soils and producing an excess of hydrogen. This hydrogen manufacturing and sequestration strategy utilizes the largest existing market for hydrogen (i.e. the production of fertilizer) and leverages the existing farm fertilizer infrastructure to restore soil carbon lost by erosion and extensive tillage. An ancillary benefit of this process is the accrual of carbon credits from capturing power plant emissions, producing a long-lived carbon soil amendment, and enhancing plant growth. If this integrated strategy ultimately proves successful, then the agricultural sector can play an inte gral role in developing the hydrogen economy and restore soil carbon, sequestering vast amounts of carbon, while increasing available nitrogen and sustained natural sequestration will occur through enhanced plant growth. Implementation could allow hydrogen production to work synergistically with fossil fuel emission reductions. A global economic stimulus is possible through profitable sequestration, increased farm productivity, local energy production, rural income opportunities, small business development and offer hope for a positive and sustainable future.

Distributed Hydrogen Production with Profitable Carbon Sequestration: A Novel Integrated Sustainable System for Clean Fossil Fuel Emissions and a Bridge to the New Hydrogen Economy and Global Socio-Economic Stability

1

Step 1. Hydrogen Production Leveraging Photosynthesis

Extract Hydrogen From Organic Matter

100-Hour Field Demonstration of Hydrogen From Biomass Catalytic Steam Reforming (August 2002)

Catalytic Steam Reforming60% H220% CO27% CO3% CH4

Plus 20% (by weight) Charcoal

But why produce charcoal?2

Step 2: Evaluation of Charcoal as a Sequestration Media and Carrier for Plant Nutrients

Charcoal Background

? Forest fires have been sequestering carbon in the soil in as charcoal for billions of years ? The half-life of charcoal in the soil is measured in 1000’s of years (Skjemstad)? Charcoal even in weathering environments can be found as old as 11,000 years old (Gavin)

A Valuable Co-Product?

We began to investigate the use of the material as a soil amendment and nutrient carrier after employees mentioned that a mound of char, used to supply char for start-up operations was covered in vegetation and more specifically turnips. Someone had tossed some turnip seeds, on the two year old, chest high, char pile. It was comprised only of char with no soil, yet on plants completely covered the mound. The plants appeared healthy with roots that enveloped each char particle. The turnips, unfortunately could not be inspected as they already had been eaten, but it was reported they were “Good!”.

The missing turnips

Charcoal is a natural part of all soil carbon content

Carbon in the Soil?Char is a pyrogenic carbon, often lumped under the classification of black carbon

? Black carbon is a term widely used for soot, an amorphous residue of combustion and a contributor to global warming. Char is not soot.

? Char found in soils from forest and range fires has a carbon framework remaining after the pyrolysis of volatile organics.

? Charcoal has proven itself with over 2000 years of testing as a soil amendment in terrapreta soils.

The Terra Preta Soil Experiment, 2000 Years Old

Terra Preta refers to black high carbon (9%) earth-like anthropogenic soil with enhanced fertility due to high levels of soil organic matter (SOM) and nutrients such as nitrogen, phosphorus, potassium, and calcium. Terra Preta soils occur in small patches averaging 20 ha. These man-made soils are found in the Brazilian Amazon basin, also in Western Africa and in the savannas of South Africa. C14 dating the sites back to between 800 BC and 500 AD. Terra Preta soils are very popular with the local farmers and are used especially to produce cash crops such as papaya and mango, which grow about three times as rapid as on surrounding infertile soils.

(Map reprinted by permission: Steiner, 2002)

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Pyrogenic Carbon Benefits• Terra Preta soils contain 15-60 Mg/ha C in 0-0.3m but 1-3Mg/ha may be

sufficient to enhance plant growth (GLASER et al.)

• Surface oxidation increased cation exchange capacity (GLASER)

• Char decreased leaching significantly (LEHMANN)

• Char traps nutrients and supports microbial growth (Pietikainen)

• Char increased available water capacity by more than 18% than surrounding soils (GLASER)

• Char experiments have shown up to 266% more biomass growth (STEINER) and 324% (Kishimoto and Sugiura)

The images above were provided for this poster by Christoph Steiner, who has been recreating Terra Preta soils in Brazil since 1999.

•Amount of applied organic matter (25% increase of Corg in 0-10 cm• Increased the soil C content ~ 0.75% •Applied Charcoal 11 t / ha•Mineral fertilizer: N (30), P (35), K (50), lime (2100 kg/ha)

International Workshop on Anthropogenic Terra Preta Soils, (July 2002 Brazil)

Current Research

1. A source for microbial energy

2. Low leaching rates

3. Internal pore structure for deposition

4. Good cation exchange

Leaching Examination of Different Chars

77.5

88.5

99.510

pH Int

itail 2 4 6 8 10 12

100ml Rinse - Char Sample 20.0g

pH

900 C

600 C

450 C

400 C

Characteristics of an Optimized Pyrogenic Fertilizer

Intra-particle volatile fatty acids deposits (Runkle et al.) occurring inside exothermic zone of pyrolysis are an excellent microbial energy source (Westjohn et al.) for processing nitrogen compounds. We speculated that near the dew point temperature a suitable material might require no outside fuel.

Leaching experiments were conducted of materials from different temperatures. Crushed and sieved (US #30 mesh), 20g samples was soaked for 5 minutes in 48% NH4NO3 solution and allowed to dry for 24 hours. Samples were leached with 100 ml rinses ( 8.0 pH). The 400C sample displayed very low leaching rates and was chosen as a starting material.

4

Step 3: Process MapAn additional benefit of the process is its ability to combine with SOx and NOx from fossil fuel exhaust. Both of the molecules are scrubbed from the exhaust to form value added nutrients.

Step 3: Process Map

Process Flow : H2 Production w/ECOSS (Patent Pending)

PyrolysisReactor#3 (Opt)

Char

Steam

Pressure Swing Adsorption

Purifier/Dryer N2

CO2

Compressor

Heat Exchanger

Catalytic Converter

CondenserRecyclingPump

FluidizedCyclone

PyrolysisOff-Gas

AmmoniaChar

Fossil Fuel Gases w/ CO2/SOx/NOx

CleanExhaust

Multistage ReleaseECOSS Fertilizer

Water

Stea

m R

efor

mer

(or

alte

rnat

e H

2Sy

stem

)

H2 + CO2

PyrolysisReactor#2 (Opt)

PyrolysisReactor

#1

CharChar

BlendingMetering

Forest Residue / Energy Crops

Nutrient Mix/PK

H2(27%)

H2 (73%) Use/Sell

(Opt. Ammonia Purchased)

5

The reactor was fed powdered char, ammonia (saturated with water), and CO2. A variable speed rotor suspended the particles and as the ammonia and CO2 derivitizedammonium bicarbonate, they would gain mass and move down the cyclone until reaching the discharge cyclone. The speed of the rotor controlled average residency time. The sand like material formed within 5-15 minutes and the larger granules (Nitrogen >10%) between 15-30 minutes.

Step 4: Bench Scale Reactor

50 kg of char was prepared at 400C. After initial heat up, no additional heat was added and the pyrolysis unit ran exothermically. The high temperature rotary value discharged the char into a closed container where it cooled. The granular material was ground and sieved to a uniform particle range. (20-30 US Mesh)

Step 4: Bench Scale Reactor

Step 5:Analysis

The exterior images show the visible build up on the outside of the particles. After crushing a particle, the formation of the ammonium bicarbonate inside the fractures and interior cavities can be clearly identified.

Formation of ABC in Fractures

Sizable Interior Cavities

Exterior Buildup as Expected

Slow Release Mechanisms

Volcano like Structures

around pores

Interior View 422x

Char

Sand like

Granular

Exterior

6

ABC Deposits

Charred Plant

FrameworkThe image below shows ammonium bicarbonate has filled the interior of the large granular particles.

Granular Interior – 1000X

Interior Image (Sand Like - 2000X)The SEM to the left is of the sand like material and was taken of the crushed interior. The charred carbon framework of the plant cell structure is visible, appearing like plastic. The volatile organics inside this char provide the needed energy source for microbial action. The ammonium bicarbonate appears as cotton-like fibers.

ABC Deposits

Charred Plant

Framework

ABC Deposits

Charred Plant

FrameworkThe image below shows ammonium bicarbonate has filled the interior of the large granular particles.

Granular Interior – 1000X

Interior Image (Sand Like - 2000X)The SEM to the left is of the sand like material and was taken of the crushed interior. The charred carbon framework of the plant cell structure is visible, appearing like plastic. The volatile organics inside this char provide the needed energy source for microbial action. The ammonium bicarbonate appears as cotton-like fibers.

Current energy use ~400Ej/yr (Lysen) and CO2 is increasing by 6.1 Gt/yr (IPCC). Each 1.0 MBTU H2/ECOSS represents 91kg (as measured, notcalculated) of sequestered CO2, then 6.1Gt/91kg equals 0.07Ej or 0.01.8% of the current world consumption of energy.

Step 6: Potential Impacts Evaluation

-100 -50 0 50 100

H2 & ECOSS

Natural Gas (Pipeline)

Liquified Petroleum Gases (LPG)

Propane

Gasoline

Diesel

Bituminous

Fuel

Carbon Dioxide per Million BTU

CO2 kg/MBTU

7

Conclusions

Material Balance and Production Limits (Energy is not the limiting factor) At theoreticalmaximum H2 –CO2 conversion there would only be enough CO2 to convert 61% of H2 toABC and since our target nitrogen content for the pyrogenic carbon is 10%, (requiring 45%carbon by weight), our limit becomes the 20% carbon char (wt. 12) vs the 56% of ABC(mol.wt. 79). The limit is therefore the carbon char as a carrier utilizing only 27% of avail-able hydrogen but sequestering 91kg of carbon dioxide (as measured experimentally) permillion BTU of hydrogen utilized for energy. In addition, there is more than 91kg when thecarbon sequestered in the form of additional plant growth and CO2 equivalents from reducedgreenhouse gas emissions from lower power plant and fertilizer NOx release.

? Hydrogen and carbon sequestration can be economically combined.

? Production of a valuable sequestering co-product during hydrogen production has a

potentially large volume application

? The material displays characteristics which will reduce nutrient leaching and loss

? Production of a nutrient inside carbon pores for physical slow release mechanism possi-

bly enhancing plant uptake and reducing fertilizer GHG emissions.

? Physical micro pore structure offers safe haven for enhanced microbial activity and in-

creased soil fertility

? Intra-particle deposition of volatile fatty acids offer microbial energy source and enhance-

ment of nitrogen compound processing.

? Increased cation exchange and water holding capacity provide better plant-soil efficien-

cies.

? Provides a stable sequestration method where existing fertilizer business infrastructure

can profit

? Offers forestry and agriculture a method to enhance carbon sequestration and fiber/crop

yields

8

Danny DayEprida6300 Powers Ferry Rd, Suite 307Atlanta, GA 30339

danny.day AT eprida.com404-228-8687http://www.eprida.com

The Potential for BiofertilisersThe growth in agricultural production during the last three decades has been accom-panied by a sharp increase in the use of chemical fertilisers, causing serious concern(Marothia, 1997). Foremost among these concerns is the effect of excessive fertiliser(especially nitrogenous fertilisers) on the quality of soil and ground water.8

Biofertilisers are considered to be an important alternative source of plant nutrition.They are biologically active products, including bacteria, algae or fungi, with the abilityto provide plants with nutrients. Most biofertilisers belong to one of two categories:nitrogen fixing and phosphate solubilising. Nitrogen fixing biofertilisers fix atmos-pheric nitrogen into forms which are readily useable by plants. These include rhizo-bium, azatobacter, azospirillum, blue green algae (BGA) and azolla. While rhizobiumrequires symbiotic association with the root nodules of legumes to fix nitrogen, otherscan fix nitrogen independently. Phosphate solubilising micro-organisms (PSM) secreteorganic acids which enhance the uptake of phosphorus by plants by dissolving rockphosphate and tricalcium phosphates. PSMs are particularly valuable as they are notcrop specific and can benefit all crops (Table 2).

Table 2. Major biofertilisers and target crops

Biofertiliser Target CropRhizobium Leguminous crops

(Pulses, oilseeds, fodder)Azatobacter Wheat, rice, vegetablesAzospirillum rice, sugarcaneBlue green algae (BGA) riceAzolla ricePhosphate solubilising microorganisms (PSMs) all

Production of biofertilisers in India

The idea of using micro-organisms to improve land productivity has been around inIndia for at least 70 years, but it was only in the 1990s that large scale production ofvarious biofertilisers commenced. Presently, a number of agricultural universities, stateagricultural departments and commercial enterprises produce various biofertilisers.

The promotion of biofertilisers is mainly carried out by the National Biofertiliser Devel-opment Centre (Ghaziabad), which was set up in 1987. The main objectives of theNational Centre are to:

8 GATEKEEPER SERIES NO .SA93

8 Water containing excess of nitrates can affect the blood’s ability to transport oxygen, with serious health implica-tions (WHO, 1963).

• produce and market biofertilisers of required quality;• isolate and maintain biofertiliser strains suitable to various agro-climatic regions;• train agricultural extension workers;• promote biofertilisers through field demonstrations;• prepare quality parameters;• test samples of biofertilisers produced by others;• provide technical and financial assistance to units producing biofertilisers.

The National Centre has the capacity to produce 375 tons of biofertilisers per year. Inaddition to this, 58 commercial production units have been set up with governmentsupport. India’s total production in 1998-99 was reported to be 16,000 tons.9 Rhizo-bium accounts for the largest proportion (40%) of the total production in India. Thisis followed by azatobacter. With the increase in the price of phosphate fertilisers, thepotential for the use of PSM has also increased.

Effectiveness of biofertilisers

A considerable amount of research has been done to establish the effectiveness of biofer-tilisers on various crops, in different agro-climatic regions. Most agricultural universi-ties, the ICAR and the National Biofertiliser Development Centre have carried out anumber of field trials to document the effectiveness of these micro-organisms. Theseprogrammes show that the use of biofertilisers can have a significant effect on the yieldof most crops. However, their effectiveness is found to vary greatly, depending largelyon soil condition, temperature and farming practices. As an example, Table 3 shows theeffect of azatobacter on yield.

Table 3. Effect of azatobacter on crop yield

Crop Increase in yield over Crop Increase in yield overyields obtained with yields obtained withchemical fertilisers (%) chemical fertilisers (%)

Food grains OtherWheat 8-10 Potato 13Rice 5 Carrot 16Maize 15-20 Cauliflower 40Sorghum 15-20 Tomato 2-24

Cotton 7-27Sugarcane 9-24

Source: Das, 1991

GATEKEEPER SERIES NO .SA93 9

9 Dr. T. Singh, pers. comm., Director, National Biofertiliser Development Centre.

The Case Study: Karnal and Bhiwani Districts, Haryana

A field study was initiated in two districts in Haryana to try to understand why biofer-tilisers and biopesticides were not being adopted on a wide scale. The study focusedon two districts: Karnal and Bhiwani. While Karnal represents intensive agriculturewith a high degree of irrigation, Bhiwani represents dryland farming, with low levelirrigation. The potential for biofertilisers and pesticides is described below, followedby the results of our interviews with farmers to establish why biofertilisers and biopes-ticdes have not been taken up more widely.

The Potential for Biopesticides and Biofertilisers in Haryana

The problems caused by excessive pesticide use are particularly serious in rice andcotton in Haryana, both important crops in our study districts. The American boll-worm, jassid and white fly in cotton; and stem borer in rice; have developed resistanceto chemicals in many parts of Haryana, including parts of the districts studied. In thissituation there is great potential for biopesticides.

The potential of biofertilisers is evidenced by the fact that about 90% of Haryana’s soilis deficient in nitrogen, indicating severe nutrient deficiency (Dahiya et al., 1993). Thedryland districts such as Bhiwani, Mohindergarh, Sirsa and Faridabad are particularlylow in nitrogen, and soils are short of organic matter due to poor vegetative cover, hightemperatures and the light texture of soil. Biofertilisers could play a role in providingthe much needed nutrients and improving soil conditions in these dryland areas, whichaccount for about 28% of the state’s total cultivable area.

Biofertilisers can also reduce the intensity of chemical fertiliser consumption, especiallyin irrigated areas. With the increase in cropping intensity (see below), the use of chem-ical fertilisers has increased significantly in these areas. The use of organic manure, onthe other hand, has not increased. As a result, many parts of Haryana face deteriorat-ing soil conditions and increasing ground water contamination.

The suitability of biofertilisers for various crops grown in Haryana has been shownthrough demonstrations conducted by the Hissar Centre of the National BiofertiliserDevelopment Centre (NBDC). Azatobacter and azospirillum, which can be used for awide range of crops, are estimated to have particularly large potential. For example,NBDC experiments showed an increase in yield between 3 and 25% with the applica-tion of azotobacter in cotton. Similarly, in the case of wheat, use of azotobacter resultedin yield increases between 2 and 20%.10


10 National project on use and development of biofertilisers. Biofertiliser News, 1(2), December 1993.


The potential for the use of rhizobium is largely confined to the dryland areas ofHaryana, where pulses are commonly grown, and where the soils show poor to moder-ate nodulation.11

Karnal DistrictIn Karnal the main nutrient and pest problems relate to the district’s high croppingintensity. Wheat-rice rotation has been common for some time now, and cropping inten-sity has recently increased further with the introduction of short duration rice varietiessuch as Govinda (90 days). Planting these varieties allows farmers to take two rice cropsbetween April and October. The first paddy crop is planted in April-May, as soon aswheat has been harvested. This rice crop is ready for harvest by mid July. This isfollowed immediately by the transplanting of fresh paddy seedlings. The second ricecrop is harvested by the end of October, to be followed by wheat, which is sown byearly November.

This very high intensity of cropping has worsened both the soil quality and pest problemin parts of Karnal. It is extremely damaging to the soil condition, as large amounts ofnutrients are used continuously without replenishment. As a new crop is planted assoon as the older crop is harvested (sometimes both activities are done simultaneously),there is no time for proper land preparation and for using organic manure. As the useof chemical fertilisers has increased to provide the required nutrients, soil and waterconditions have deteriorated.

The problem of pests and pesticide use in Karnal is largely confined to rice. Growingtwo rice crops without a break is one factor. The continuation of rice plants in the samefield, and the high degree of moisture, enable pests to multiply without a break, leadingto particularly intense pest attacks in the second crop. Another reason is the popular-ity of certain basmati varieties which are highly susceptible to pests and diseases. Thisis particularly serious in one of the most popular of these varieties, called duplicatebasmati. This variety was introduced about five years ago from West UP, and becamevery popular because of its high yields,12 and totally replaced the desi (traditional)basmati variety in many areas. After performing well for three years, the variety beganto be affected by pests (stem borer, leaf folder and white back plant hopper) and diseases(sheath blight, blast and bacterial leaf blight) two years ago. The attack was particu-larly severe last year, forcing many farmers to stop planting basmati in general, andduplicate basmati in particular. In one of the villages we studied, Kuuchhpura, farmersmade up to 15 pesticide applications last year but could not save the crop. This year,very few farmers have planted basmati in the village.

11 The assimilation of atmospheric nitrogen by the roots of pulse (and other leguminous) crops is carried outby the nodules formed in the roots of these plants. The low degree of nodulation suggests that their ability toassimilate atmospheric nitrogen is low and that they could benefit from the use of rhizobium.12 Compared to the average yield of 10 quintal/acre from desi basmati, the yields of duplicate basmati wereabout 20 quintal/acre.

The problem of pesticide resistance in stem borer is now common in Karnal, largelycaused by the indiscriminate and excessive use of pesticides. Another important reasonrelates to the fact that farmers in Karnal do not spray their fields themselves. This isdone by professional workers who are sent by the shops selling pesticides. As theseworkers are paid by the area covered, they do a rushed job. The spraying is not uniform:while some parts of the fields get very little, others get excessive pesticides. Secondly,in order to save time they use about one third of the water prescribed to make the pesti-cide solution. The non-uniform spray of highly concentrated pesticide solution isreported to be a major reason for the development of resistance in rice pests in manyparts of the district.13

Bhiwani DistrictIn Bhiwani, the focus of the study is on cotton and gram, which, along with wheat andmustard are the main crops in the area. The use of chemical fertilisers is comparativelylow in Bhiwani, being used only on wheat and cotton, and not at all on gram andmustard. But, as in Karnal, use of organic manure is not common and the condition ofthe soil is poor. Three biofertilisers have potential for Bhiwani: rhizobium for gram andazatobacter and PSM for wheat. The potential of rhizobium is reported to be particu-larly high in Bhiwani because the level of nodulation is very low.

The District Agriculture Department is responsible for the sale of rhizobium in Bhiwani.Being a major gram growing district, it was allocated the largest amount of rhizobiumlast year and its sale to farmers is subsidised at the rate of 50%.

The main pest problem in Bhiwani concerns cotton, which is attacked by American,pink and spotted bollworm, white fly and jassid. These pests have become resistant tomost pesticides. According to a study of pesticide use in Bhiwani in 1998, about 70%of farmers reported that they were unable to control pests with pesticides (Saini andJaglan, 1998). Some of these farmers had used up to 11 pesticide applications.

The pest problem in Bhiwani is closely linked with the spread of irrigation facilities.Large parts of Bhiwani district are irrigated by the Indira Gandhi Canal, which suffersfrom large scale seepage. This has led to a rise in the groundwater level from 50-60 feetbelow the surface in the past to 5-10 feet at present in many areas. As a result, waterlogging and high humidity are serious problems in many areas of the district. Apartfrom causing direct damage, this has also created favourable conditions for the growthof pests. Consequently, the problem of pests has become extremely serious in the districtduring the last five years.

The pest problem caused the area under cotton to decline in the second half of the1990s from 57, 000 hectares in 1996-97 to 51,000 hectares in 1999-2000.14 As in rice


13 Information from the District Agricultural Officers.14 Information provided by the State Agricultural Department, Bhiwani.


in Karnal, the pest problem in cotton in Bhiwani is closely related to the susceptibilityof the varieties being planted. The cultivation of cotton in this area is comparativelynew: it was introduced in the 1970s. Most of the varieties introduced since then arelong staple, American types. Although they fetch high prices, they are highly suscepti-ble to various cotton pests. The problem of pests and the excessive use of pesticides inBhiwani is mostly confined to the American varieties. Desi varieties, which are compar-atively resistant to pests and diseases, require less use of pesticides.

We observed a shift back in favour of desi cotton in one of the divisions of Bhiwanifollowing severe losses to pests to the American varieties. Whilst many more farmerswould prefer to shift to desi cotton varieties, as they provide stable yields, their whole-sale prices are too low. In addition it appears that the state agriculture departmentprefers to promote long staple American varieties, as they have large domestic andexport markets.

Farmers’ Perspectives

We selected 11 villages from the two districts, six villages from Karnal and five fromBhiwani, in which to interview farmers to establish their awareness and use of biofer-tilisers and biopesticides. A total of 74 farmers from these villages were interviewed, andwere mainly selected because they had attended one of the demonstration programmescarried out by government agencies to promote IPM, biopesticides and biofertilisers(58 of the farmers, or about 80% of the sample). However, some farmers who had notbeen to the programmes were also interviewed (16 farmers). All the farmers were men;only men had participated in the demonstration programmes, and we were told thatmen take the decisions about the types of fertilisers and pesticides to be used.

The farmers included in the study represent the range of small, medium and largefarmers. While 29% of the farmers have less than 5 acres of land, 46% have between5 and 20 acres. 25% of the farmers have landholdings larger than 20 acres. In termsof education, about one third of the farmers have studied up to class 10 or more. Asemi-structured questionnaire was used for interviews, which were conducted infarmers’ homes.

Findings: Biopesticides

Although biopesticides and bio-control agents are important components of IPM, theIPM programmes being conducted by various agencies put very little emphasis on theseagents. None of the farmers we interviewed had ever used biopesticides, and few wereeven aware they existed. We found that none of the farmers had even used neem, widelybelieved to be commonly used by Indian farmers.

In fact, we found that IPM itself was not being practised by most farmers. While someof the farmers were aware of IPM practices, such as the need for monitoring and

augmenting natural enemies of pests, very few farmers have adopted these practices.None of the farmers practised IPM fully, but about 15% practised partial IPM. In mostcases this meant delaying the first spray of pesticides until damage by pests becomesevident. The situation is particularly bad in Bhiwani, where 85% of farmers reportednot using IPM at all and only 9% reported using some aspects of IPM. Compared tothis, 20% of farmers reported using limited IPM in Karnal. This is despite the fact thatmost of the farmers included in the study participated in the IPM demonstrationprogrammes conducted by the Central IPM.

Why is IPM not practised?We found four important reasons for the low acceptance of IPM:

1. Lack of awareness. This reason was found to be particularly important in Bhiwani,where 77% of farmers were unaware of the concepts of IPM. Compared to this, fewerthan 3% of farmers in Karnal were unaware of IPM. Clearly, there is a big district-wise difference in the success of IPM demonstration programmes and state agriculturalextension workers in familiarising farmers with IPM. In Karnal these agencies havebeen successful in at least making farmers aware of the need to practise IPM.

2. Lack of skills. Almost all the farmers, including all of those who were aware of IPM,reported that they lacked the skills necessary to practise IPM. Their ability to practiseIPM was, for example, severely constrained by the fact that most of them could not differ-entiate between harmful and beneficial insects. In fact, many farmers thought that allinsects were a potential threat to their crop and had to be destroyed. They were also notable to work out economic thresholds15 to determine the timings of pesticide application.

3. Lack of faith in IPM. This factor was found to be very important amongst 60% offarmers in Karnal. Although almost all of them were aware of IPM, they felt that theydid not have sufficient faith in it to reduce the use of chemical pesticides. Many ofthem felt that the support from the agricultural department was not adequate for themto try IPM practices, which were considered risky. As the CIPM personnel do not keepin touch with the farmers after IPM demonstrations, they felt that they would not getadequate advice and support if things went wrong. Similarly, the local extensionworkers (ADOs) are not sufficiently trained in IPM to instil confidence in the farmers.

The issue of skills and confidence is obviously linked to the intensity of trainingprovided by the IPM agencies to farmers and extension workers. We found that thetraining is very basic and superficial, being conducted for three to four days in avillage, during which 30 villagers and five extension workers are trained. The farmersfelt that the training was not intensive and did not impart sufficient skills for themto feel competent and confident in following IPM practices.


15 The economic threshold is the level of pest population at which the damage to crop justifies the use of pestcontrol methods.


4. IPM practices are difficult and cumbersome. About 70% of the farmers in bothdistricts who were aware of IPM, felt that the IPM practices were too cumbersomeand time consuming to be used regularly. Both the monitoring of pest populationsand the calculation of economic thresholds were considered by farmers to be imprac-tical. In Karnal, where cropping intensity is high, the farmers felt that they did nothave time to keep a close watch on their fields to monitor pests and calculateeconomic thresholds.

Whose advice is taken?An important reason for the failure of the IPM programme, and the lack of biopesti-cide use, is related to the fact that most farmers depend on shopkeepers for advice onpesticide application. More than 80% of the farmers reported that shopkeepers, dealersand representatives of pesticide manufacturers were their most important sources ofinformation about pest control methods (Table 4).

Table 4. Importance of source of advice for pesticide application

Other Extension Shops/manufacturers/ Farmers workers and dealers

agricultural universityKarnal 12 (30) 18 (45) 33 (83)Bhiwani 10 (30) 9 (26) 27 (80)Total 22 (30) 27 (36) 60 (81)

Number of responses=74. Note that some farmers listed more than one source of advice as beingequally important

Note: Figures in parenthesis indicate percentages.

Compared to the manufacturers and sellers of pesticides, agricultural extension workersplay a small role, especially in Bhiwani, where only 26% of farmers reported them tobe important.

The role of shopkeepers and dealers is particularly important because many farmers(58%) purchase their pesticides on credit. This gives the shopkeepers strong controlover the amount and choice of pesticides used. It also makes it easier for the shop-keepers to sell spurious pesticides.

Finally, we found that the knowledge of the State Agricultural Department aboutbiopesticides was extremely limited. This was particularly true of the village levelworkers (ADOs), but also the case even in the Central IPM office in Faridabad. Consid-ering the importance given to the use of biopesticides by national government agen-cies, the neglect of biopesticides at the state and district level is difficult to understand.The main emphasis is on the monitoring of pest populations and the use of economicthresholds, which farmers find too difficult and time consuming. Further, the Haryana

Agricultural University recommends the use of only two biopesticides (Bt and neem) ononly one vegetable crop. On all other crops, including cotton and rice, the recommen-dations include only chemical pesticides.

Findings: Biofertilisers

Few (19%) farmers have ever used biofertilisers in the two districts. Their number wasespecially small in Karnal, where only three out of 40 farmers had used them. InBhiwani about 75% of farmers were not even aware of biofertilisers; the proportion ofsuch farmers was even higher in Karnal (85%).

The most important reason for this lack of awareness is the fact that agriculture exten-sion workers do not promote biofertilisers. On the whole, only 15% of farmers hadbeen told about biofertilisers by the extension workers. The emphasis on biofertiliserswas particularly low in Karnal, where only one farmer out of 40 had heard about themfrom extension workers.

The District Agricultural Departments do not have a positive attitude towards biofer-tilisers. They feel that their quality is poor, and their performance totally unreliable.Therefore, they are not prepared to risk their reputation and good will with the farmersby recommending them. The extension services run by the Haryana Agriculture Univer-sity (krishi vigyan kendra) feel that in areas of wheat/paddy rotation, such as Karnal,the potential of biofertilisers is low. The farmers in these areas can get the same yieldby using the recommended dose of chemical fertilisers. As these fertilisers are easy touse, the farmers prefer them. Biofertilisers have to be stored and applied in conditionswhich are suitable for the multipication of micro-organisms. This requires special facil-ities and care, which farmers are often unable to provide. Chemical fertilisers, on theother hand, can be stored and applied without special care. In fact, the KVK in Karnaldoes not recommend the use of biofertilisers at all.

Nevertheless, the extension workers in Bhiwani are required to sell a fixed number ofrhizobium packets. This explains the larger number of farmers who are aware of biofer-tilisers, and have used them in this district. But we found that a large proportion of therhizobium allotted to the district is not sold to the farmers, and is allowed to go towaste. The ADOs say that the quality and performance is so poor that the farmers arenot interested in buying it. The quota is shown as sold in official records, and thepayment is made by the ADOs from their salary.16 The fact that the rhizobium meantfor sale in various pulse growing districts is not being used by farmers is widely knownto both the State Agricultural Department and the National Biofertiliser Development


16 For example, one of the ADOs in Bhiwani was given a quota of 2000 packets of rhizobium this year. Hecould manage to sell only about 200 packets, mostly to his contact farmers. But these have not actually beenused by the farmers. He feels that the contact farmers accept biofertilisers because they want to stay in the goodbooks of the ADOs, from whom they receive subsidised or free goods, such as seed kits. He will have to payto the Agricultural Department Rs. 8,000/- (@Rs. 4.00 a packet).

Centre. However, every year the practice of fixing quotas and reporting of sale is carriedout, as if rhizobium is actually being used.

Out of 19 farmers who were aware of biofertilisers, 14 had used them, showing thatfarmers are prepared to try biofertilisers. However, most of these farmers stopped usingthem after one crop - only three were still using them. Two reasons were reported tobe important for the discontinuation of use: lack of availability and poor performance.

AvailabilityMany farmers who stopped using biofertilisers reported that this was partly because thesupply was extremely unreliable. This was largely because biofertilisers were not beingsold by most shops. While none of the shops stock biofertilisers in Karnal, two shopsin Bhiwani do. The shopkeepers, in turn, say that they do not stock biofertilisersbecause sales are poor. One of the Bhiwani shops, for example, has been stocking biofer-tilisers from National Fertilisers Ltd. for the last four years but has sold only 30 packets.

QualityIt is clear that the poor quality and performance of biofertilisers present serious prob-lems. Most studies suggest that the biofertilisers being sold in the market are contam-inated and have a low count of micro-organisms. It is therefore not surprising that theirperformance is poor and uneven. For example, in a survey of rhizobium carried out byICRISAT, 90% of samples from India were found to have a rhizobia count lower thanthat required for effective performance (Singleton et al., 1996). Incidentally, thisproblem exists in most developing countries. For example, in a survey of 12 develop-ing countries, only 19% of the samples met the standards prevalent in developed coun-tries (Singleton et al., 1996).

The poor performance of biofertilisers in India is primarily linked to inappropriatestrains and inefficient production technology. Essentially, the production of bacterialbiofertilisers requires the selection of strains appropriate for a particular crop in a givenagro-climate. These strains are mass multiplied by adding bacterial culture to a suit-able sterilised broth, either using the shake flask method (for small scale production)or the fermenter method (for large scale production). When an adequate growth ofbacteria is achieved, the solution is mixed with a carrier such as lignite or charcoal andis packaged.

As agro-climatic conditions and soil characteristics vary widely, a large range of strainsof each biofertiliser needs to be isolated for each area. The problem of identifying suit-able strains is particularly serious in north India, as many of the strains do not survivethe very hot temperatures prevalent in these areas. Until strains which can tolerate widevariations in temperature can be identified, the performance of biofertilisers will remainuneven. The Haryana Agriculture University is reported to be working in this directionand has developed improved strains for pearl millet, wheat, mustard, potatoes, andflowering plants. These are, however, yet to be used in large scale production.


Furthermore, the production of biofertilisers is prone to contamination, which reducesthe effectiveness of micro-organisms. It is, therefore, vitally important that throughoutthe process extreme care is taken to maintain sterile conditions. It is also importantthat precautions are taken to avoid contamination during the packaging, storage andapplication of biofertilisers.

The production technology employed in India is inefficient and is responsible for mostof the contamination common in Indian biofertilisers. Generally, production is under-taken by the flask method, which is unsuitable for large scale production. Althoughsome firms use fermenters, they lack the sophisticated controls and monitoring facili-ties necessary to regulate factors such as pH, temperature and aeration. As a result thequality of the bacterial broth is often poor and uneven.

Another problem relates to the fact that Indian producers do not sterilise the carriersused for mixing the bacterial solution. For example, both the producers in Haryana, theHissar Biofertiliser Centre and the HAU, use non-sterilised charcoal, as they do nothave facilities to sterilise large amounts of charcoal in a short time. This is an impor-tant cause of the poor quality and short shelf life of these biofertilisers (Singh et al.,1999). Although India has ISI (Indian Standards Institution) standards for some of thebiopesticides (rhizobium and azatobacter), they are not enforced. This is reportedlybecause the ISI lacks facilities to test biofertilisers.

ConclusionsBiopesticides

The problem of pests, the development of pesticide resistance and the excessive use ofpesticides need to be seen in the totality of the agricultural system. Our study shows thatin Karnal and Bhiwani the problem is linked to the increase in cropping intensity (threecrops in Karnal), the expansion of irrigation facilities (Bhiwani), the release and adop-tion of susceptible varieties (govinda and basmati rice in Karnal, and American cottonvarieties in Bhiwani), purchase of pesticides on credit (in both the districts) and inap-propriate agricultural practices (the use of contract labour for pesticide application,using power spraying machines in Karnal). In the circumstances, mere reliance on pestcontrol, without correcting the basic problem in the system, will not produce sustain-able results.

The efforts of various government agencies to popularise integrated pest management(IPM), and the use of biopesticides have had little impact. IPM departments have verylittle knowledge and experience of biopesticides, and most state agricultural universi-ties, on whose recommendations pest control methods are promoted, do not include theuse of biopesticides in their recommendations. In the absence of active promotion bythe agriculture department, the demand for these products has not developed. It is forthis reason that most private shops and dealers do not stock and sell biopesticides.

18 GATEKEEPER SERIES NO .SA9318 GATEKEEPER SERIES NO .SA91

A Study ofBiopesticides andBiofertilisers inHaryana, India

Ghayur Alam

2000

Gatekeeper Series no. 93

Submitting papers to the Gatekeeper SeriesWe welcome contributions to the Gatekeeper Series from researchers and practitioners alike. The Series addresses issues of interest to policy makers relatingto the broad area of sustainable agriculture and resource management.Gatekeepers aim to provide an informed briefing on key policy issues in a readable, digestible form for an institutional and individual readership largelycomprising policy and decision-makers within aid agencies, national governments,NGOs and research institutes throughout the world. In addition to this primaryaudience, Gatekeepers are increasingly requested by educators in tertiary education institutions, particularly in the South, for use as course or seminar discussion material.

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Editorial processPlease send two hard copies of your paper. Papers are reviewed by the editorialcommittee and comments sent back to authors. Authors may be requested tomake changes to papers accepted for publication. Any subsequent editorialamendments will be undertaken in consultation with the author. Assistance withediting and language can be provided where appropriate.

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Gatekeeper EditorSustainable Agriculture and Rural Livelihoods Programme IIED, 3 Endsleigh Street, London WC1H ODD, UK Tel:(+44 020) 7388 2117; Fax: (+44 020) 7388 2826; e-mail: [email protected]

GATEKEEPER SERIES NO.SA93 1

The Gatekeeper Series produced by IIED’s Sustainable Agriculture and Rural Liveli-hoods Programme aims to highlight key topics in the field of sustainable agricultureand resource management. Each paper reviews a selected issue of contemporary impor-tance and draws preliminary conclusions for development that are particularly relevantfor policymakers, researchers and planners. References are provided to importantsources and background material. The Series is published three times a year – in April,August and December – and is supported by the Swedish International DevelopmentCooperation Agency (Sida).

The views expressed in this paper are those of the author(s), and do not necessarilyrepresent those of the International Institute for Environment and Development (IIED),The Swedish International Development Cooperation Agency (Sida), or any of theirpartners.

Dr Ghayur Alam is Director of the Centre For Technology Studies in New Delhi. Hismain areas of interest include technology policy, intellectual property rights,agricultural biotechnology and the adoption of environmentally suitable technologiesin industry and agriculture. He can be contacted at: Centre For Technology Studies,U 24/20, DLF III, Gurgaon, Haryana 122002, India. Email: [email protected]: +91 (0124) 6355942; Fax: +91 (0124) 6358322

2000

2 GATEKEEPER SERIES NO.SA93

Executive SummaryThe use of chemical pesticides and fertilisers in Indian agriculture has seen asharp increase in recent years, and in some areas has reached alarming levelswith grave implications for human health, the ecosystem and ground water. It istherefore increasingly urgent that environmentally friendly methods of improv-ing soil fertility and pests and disease control are used.

The potential of biopesticides and biofertilisers for promoting sustainable agri-culture has been known for many years. A number of government agencies,including the Ministry of Agriculture and the Department of Biotechnology, areengaged in supporting research, production and application of these agents.However, in spite of these efforts, their use in India is small. This paper investi-gates the potential of and constraints in the use of biopesticides and biofertilis-ers, taking the state of Haryana as a case study. It explores the factors responsi-ble for the limited use of these agents, based on detailed discussions with alarge number of farmers, various agencies engaged in the promotion of biopes-ticides and biofertilisers, State Agricultural Department officials, and shopkeep-ers.

The study found that for the use of biopesticides, a key problem was thatdepartments promoting Integrated Pest Management (IPM) have very littleknowledge and experience of biopesticides, and most state agricultural universi-ties, on whose recommendations pest control methods are promoted, do nottend to recommend biopesticides. In the absence of active promotion by theagriculture department, the demand for these products has not developed, andmost private shops and dealers do not stock and sell biopesticides. The paperrecommends that the agricultural departments and universities pay greaterattention to the promotion of biopesticides, that IPM training is improved, andthat there is a greater focus on cropping techniques and varieties which do notrequire such a dependence on pesticides.

In the case of biofertilisers, their poor quality and performance is a major factorin their limited uptake by farmers. This is primarily linked to inappropriatestrains and inefficient production technology. As a result it is recommended thatresearch and development to identify more suitable strains, to develop betterproduction technology and quality control methods is greatly increased, andthat in the meantime the various grants and subsidies on biofertilisers are divert-ed to support these R&D programmes.

A Study of Biopesticides and Biofertilisers inHaryana, India

Ghayur Alam

IntroductionThe use of chemical pesticides and fertilisers in Indian agriculture has seen a sharpincrease in recent years. In some areas, such as Haryana, Punjab and west UttarPradesh, it has reached alarming levels. The heavy use of these chemicals has alreadycaused grave damage to health, ecosystems and ground water. It is therefore increasinglyurgent that environmentally friendly methods of improving soil fertility and pests anddisease control are used.

The potential of biopesticides and biofertilisers for promoting sustainable agriculturehas been known for many years. A number of government agencies, including theMinistry of Agriculture and the Department of Biotechnology, are engaged in support-ing research, production and application of these agents. However, in spite of theseefforts, their use in India is small. This paper investigates the potential of and constraintsin the use of biopesticides and biofertilisers, and explores the factors responsible forthe limited use of these agents. It is based on a study in the state of Haryana, a statewhich represents the problem of excessive use of pesticides and fertilisers, common inmany parts of India. The paper also suggests policy measures for the promotion ofbiopesticides and biofertilisers in the state. The study is based on detailed discussionswith a large number of farmers, various agencies engaged in the promotion of biopes-ticides and biofertilisers, State Agricultural Department officials, and shopkeepers. Thestudy was carried out in 1999 as part of a research project on agricultural problems,undertaken by the Agricultural Economics Research Centre, University of Delhi.

The Potential for BiopesticidesAbout 80,000 tons of pesticides are used in agriculture in India annually (Srinivasan,1997), mostly in cotton and rice. While cotton is planted on about 5% of the totalcultivable area (on about 8 million hectares out of a total of 170 million), it accountsfor about 45% of pesticide application (Dhaliwal and Pathak, 1993). Rice accountsfor another 23%. Vegetables and fruit also account for a significant proportion (Table1).


Table 1. Cropwise consumption of pesticide in India (%)

Cotton 44.5Paddy 22.8Jowar 8.9Fruits and Vegetables 7.0Wheat 6.4Arhar 2.8Other 7.6Total 100.00

Source: Dudani and Sengupta, 1991

The intensive use of pesticides in agriculture is a cause of serious concern. The problemis especially serious because of the development of resistance to pesticides in importantpests and the presence of pesticide residue in agricultural and dairy products.

Pesticide resistance in agriculture was first noticed in India in 1963 when a number ofserious pests were reported to have become resistant to DDT and HCH (two of themost commonly used pesticides during the 1960s and 1970s). Since then the numberof pests with pesticide resistance has increased. The most serious problem of resistanceis witnessed in cotton, for which American bollworm is a serious pest. The bollwormhas developed resistance to almost all pesticides in a number of regions, and is partic-ularly serious in parts of Punjab, Haryana, Andhra Pradesh, Karnataka and Maha-rashtra. Other important pests of cotton, white fly and jassid, have also developedpesticide resistance in some places.

Growing pesticide resistance has meant that a large proportion of agricultural produc-tion is lost to pests. According to some estimates, these losses amount to between 20-30% of total production (Mehrotra, 1989). The losses are particularly serious in cotton.For example, cotton production in Punjab declined by about 50% during 1997 and1998,1 causing a number of cotton farmers to commit suicide in the affected areas.2

Pesticide resistance has mainly been caused by excessive and indiscriminate use of pesti-cides (Jayaraj, 1989). Pesticides of spurious quality, which are commonly sold in smalltowns and villages, have also contributed to resistance in many areas. For example, inBidar (Karnataka) where the problem of pest resistance has become extremely serious,more than 50 brands of pesticides were found to be sub-standard in 1998-99. In anotherincident, the licenses of 115 pesticide producers were cancelled in Punjab for selling


1 “Another bad season for cotton farmers”, Hindustan Times, September 17, 1998.2 For example, in Punjab 133 farmers were reported to have committed suicide in 1998 due to crop failurecaused by pest attack. “Another farmer in debt trap commits suicide”, Hindustan Times, October 4, 1998.


sub-standard pesticide.3 Sub-standard pesticides contribute to resistance as the pestsare repeatedly exposed to a low concentration of pesticides. This contributes to thebuild-up of resistance, without destroying the pests.

The other important problem caused by the excessive and inappropriate use of chem-ical pesticides concerns the presence of pesticide residue in food. Many of the pesti-cides currently being used have a tendency to survive in plants for a long time. They alsoenter the food chain and are found in meat and dairy products. The problem of pesti-cide residue is already a serious threat to health and environment in India. The inci-dence of pesticide residue is much higher in India than in developed countries. Forexample, according to one study, more than 80% of milk samples tested in India werefound to contain residues of DDT and HCH (Handa, undated). According to anotherstudy, residue of DDT and benzene hexachloride, both suspected carcinogens, werefound in breast milk samples collected from mothers in Punjab. The amount of residuewas very high and babies were ingesting 21 times the amount of these chemicals consid-ered acceptable through their mothers’ milk (Jumanah, 1994).

Compared to this, only 0.17% of samples tested in the US in 1990 were found tocontain residues over the acceptable limits.4 Similarly, in a study in the UK, only 1% ofthe samples were found to contain residues above the prescribed limit.5

It is clear that the excessive use of chemical pesticides in agriculture is a serious causeof concern. It is, therefore, important that alternative, environmentally friendly methodsof plant protection are adopted, such as integrated pest management (IPM) techniques,including the use of biopesticides.

Biopesticides and Bio-control Agents

Biopesticides are derived from animals, plants and micro-organisms such as bacteriaand viruses. The advantages of biopesticides are:

• They are inherently less harmful than chemical pesticides;• They are more target specific than chemical pesticides affecting only the target pests

and their close relatives. In contrast, chemical pesticides often destroy friendly insects,birds and mammals.

• They are often effective in small quantities. Also, they decompose quickly and do notleave problematic residues.

The most commonly used biopesticides include Bacillus thuringiensis (Bt), Baculovirusesand neem. In addition to these, trichoderma, which is a fungicide, is also used. Bio-control agents, such as Trichogramma, are parasites and predators of pests and their

3 “Another bad season for cotton farmers”, Hindustan Times, September 17, 1998.4 “Current Pesticide Residue Levels in Food are Safe”, Pesticide Outlook (5)1, Feb 94. Cambridge.5 “Latest UK Pesticide Residue Results Published”, Pesticide Outlook, Dec 1994, pp8. Cambridge.


eggs. These biopesticides and bio-control agents are briefly described below:

• Bacillus thuringiensis (Bt). Bacillus thuringiensis is the most commonly used biopes-ticide globally. It is primarily a pathogen of lepidopterous pests which are some ofthe most damaging. These include American bollworm in cotton and stem borers inrice. When ingested by pest larvae, Bt releases toxins which damage the mid gut ofthe pest, eventually killing it. Bt based pesticides are being marketed by three compa-nies in India. The total sale in 1999 was about 70 tons.6

• Baculoviruses. These are target specific viruses which can infect and destroy a numberof important plant pests. They are particularly effective against the lepidopterouspests of cotton, rice and vegetables. Their large-scale production poses certain diffi-culties, so their use has been limited to small areas. They are not available commer-cially in India, but are being produced on a small scale by various IPM centres andstate agricultural departments.

• Neem. Derived from the neem tree (Azadirachta indica), this contains several chem-icals, including ‘azadirachtin’, which affects the reproductive and digestive processof a number of important pests. Recent research carried out in India and abroad hasled to the development of effective formulations of neem, which are being commer-cially produced. As neem is non-toxic to birds and mammals and is non-carcinogenic,its demand is likely to increase. However, the present demand is very small. Althoughmore than 100 firms are registered to produce neem-based pesticides in India, only ahandful are actually producing it. Furthermore, very little of the production is soldlocally, most being for export markets.

• Trichoderma. Trichoderma is a fungicide effective against soil born diseases such asroot rot. It is particularly relevant for dryland crops such as groundnut, black gram,green gram and chickpea, which are susceptible to these diseases. Three companiesare marketing trichoderma in India.

• Trichogramma. Trichogramma are minute wasps which are exclusively egg-parasites.They lay eggs in the eggs of various lepidopteran pests. After hatching, theTrichogramma larvae feed on and destroy the host egg. Trichogramma is particularlyeffective against lepidopteran pests like the sugarcane internode borer, pink bollwormand sooted bollworms in cotton and stem borers in rice. They are also used againstvegetable and fruit pests. Trichogramma is the most popular bio-control agent inIndia, mainly because it kills the pest in the egg stage, ensuring that the parasite isdestroyed before any damage is done to the crop. A number of countries produceTrichogramma on a large scale. For example, in the former Soviet Union more than10 biological factories were reported to produce about 50 billion Trichograma andother parasites per season. Similarly, more than 50 commercial insectaries are reported

6 Dr MC Sharma, pers. comm. Director, Biotech International, New Delhi.


to be producing Trichogramma and other parasites in the USA and Canada. A numberof communes in China are also known to produce Trichogramma on a large scale.

Whilst India does not have technology to produce Trichogramma on a large scale, theyare being produced in small scale facilities for local use, mostly by sugar mills and coop-eratives, state agricultural departments, IPM centres and agricultural universities.Recently, some companies have started marketing Trichogramma through direct selling.But the volume of sale is very small. Trichogramma eggs have to be used within a shortperiod (before the eggs hatch). This limits their production and marketing on a largescale, and is also the reason why Trichogramma is not sold through dealers and shop-keepers.

Promotion and effectiveness of Integrated Pest Management andbiopesticides

The Ministry of Agriculture and the Department of Biotechnology are responsible forpromoting biopesticides, the former via the Central IPM Centre (Faridabad), theNational Centre for IPM (NIPM) under the Indian Council For Agricultural Research(ICAR) and the Directorate of Biological Control. As a part of the Department ofBiotechnology’s demonstration programme, biopesticides have been demonstrated onabout 55,000 hectares (Wahab, 1998). The Department has also supported a pilot plantat the Tamil Nadu Agricultural University (Coimbatore) to develop and demonstrateproduction and application technologies for baculoviruses, trichoderma andTrichogramma.

Some Integrated Pest Management (IPM) demonstrations have shown success incontrolling pests without the use of chemical pesticides. For example, NIPM carriedout a demonstration in rice in a village in west UP on 100 acres in 1999. NIPM totallysubstituted chemical pesticides with the bio-control agent Trichogramma, which is effec-tive against both stem borer and leaf folder. According to NIPM, the control of pestswas complete and the yields were between 6-7 tons/hectare. Compared to this, the yieldin the area where chemical pesticides were applied was only 3.5 to 4 tons per hectare(Damodran, 1999).

In another successful demonstration by NIPM on cotton in Maharashtra during 1998-99, Baculoviruses, neem and Trichogramma were found to be more effective in control-ling pests than chemical pesticides. The yield in these plots was about 1 ton/hectare,compared to yields of only 300 to 500 kilograms/hectare in the fields where chemicalpesticides were used.7

7 “Integrated Pest Management Module for Dryland Regions - ICAR Trials in Cotton Fields Successful”.Hindu Business Line, 4.1.1999.

The Potential for BiofertilisersThe growth in agricultural production during the last three decades has been accom-panied by a sharp increase in the use of chemical fertilisers, causing serious concern(Marothia, 1997). Foremost among these concerns is the effect of excessive fertiliser(especially nitrogenous fertilisers) on the quality of soil and ground water.8

Biofertilisers are considered to be an important alternative source of plant nutrition.They are biologically active products, including bacteria, algae or fungi, with the abilityto provide plants with nutrients. Most biofertilisers belong to one of two categories:nitrogen fixing and phosphate solubilising. Nitrogen fixing biofertilisers fix atmos-pheric nitrogen into forms which are readily useable by plants. These include rhizo-bium, azatobacter, azospirillum, blue green algae (BGA) and azolla. While rhizobiumrequires symbiotic association with the root nodules of legumes to fix nitrogen, otherscan fix nitrogen independently. Phosphate solubilising micro-organisms (PSM) secreteorganic acids which enhance the uptake of phosphorus by plants by dissolving rockphosphate and tricalcium phosphates. PSMs are particularly valuable as they are notcrop specific and can benefit all crops (Table 2).

Table 2. Major biofertilisers and target crops

Biofertiliser Target CropRhizobium Leguminous crops

(Pulses, oilseeds, fodder)Azatobacter Wheat, rice, vegetablesAzospirillum rice, sugarcaneBlue green algae (BGA) riceAzolla ricePhosphate solubilising microorganisms (PSMs) all

Production of biofertilisers in India

The idea of using micro-organisms to improve land productivity has been around inIndia for at least 70 years, but it was only in the 1990s that large scale production ofvarious biofertilisers commenced. Presently, a number of agricultural universities, stateagricultural departments and commercial enterprises produce various biofertilisers.

The promotion of biofertilisers is mainly carried out by the National Biofertiliser Devel-opment Centre (Ghaziabad), which was set up in 1987. The main objectives of theNational Centre are to:


8 Water containing excess of nitrates can affect the blood’s ability to transport oxygen, with serious health implica-tions (WHO, 1963).

• produce and market biofertilisers of required quality;• isolate and maintain biofertiliser strains suitable to various agro-climatic regions;• train agricultural extension workers;• promote biofertilisers through field demonstrations;• prepare quality parameters;• test samples of biofertilisers produced by others;• provide technical and financial assistance to units producing biofertilisers.

The National Centre has the capacity to produce 375 tons of biofertilisers per year. Inaddition to this, 58 commercial production units have been set up with governmentsupport. India’s total production in 1998-99 was reported to be 16,000 tons.9 Rhizo-bium accounts for the largest proportion (40%) of the total production in India. Thisis followed by azatobacter. With the increase in the price of phosphate fertilisers, thepotential for the use of PSM has also increased.

Effectiveness of biofertilisers

A considerable amount of research has been done to establish the effectiveness of biofer-tilisers on various crops, in different agro-climatic regions. Most agricultural universi-ties, the ICAR and the National Biofertiliser Development Centre have carried out anumber of field trials to document the effectiveness of these micro-organisms. Theseprogrammes show that the use of biofertilisers can have a significant effect on the yieldof most crops. However, their effectiveness is found to vary greatly, depending largelyon soil condition, temperature and farming practices. As an example, Table 3 shows theeffect of azatobacter on yield.

Table 3. Effect of azatobacter on crop yield

Crop Increase in yield over Crop Increase in yield overyields obtained with yields obtained withchemical fertilisers (%) chemical fertilisers (%)

Food grains OtherWheat 8-10 Potato 13Rice 5 Carrot 16Maize 15-20 Cauliflower 40Sorghum 15-20 Tomato 2-24

Cotton 7-27Sugarcane 9-24

Source: Das, 1991


9 Dr. T. Singh, pers. comm., Director, National Biofertiliser Development Centre.