chapter 3_material & method

Chapter 3 Materials and Methods

Chapter 3

MATERIALS AND METHODS

Different experimental approaches were used to accomplish the stipulated objectives.

The research was carried out into different phases using various waste material

combinations. The detailed methodology is given in this chapter.

3.1 THE COMPOST MATERIAL

Cattle (Buffalo) manure, mixed vegetable wastes (uncooked), food waste (pulses and

cooked vegetable), grass cuttings, paper waste, dry tree leaves and saw dust were used for

preparation of different waste mixtures based on various C/N ratios. These are the major

ingredients of municipal solid waste generated in Indian cities (CPCB, 2006). Cattle manure

(C/N=20) was obtained from Tyagi dairy near the campus. Mixed vegetable wastes

(C/N=18) and food waste (C/N=16) collected from student hostels including Jawahar,

Sarojini, Ravindra, Govind and Azad Bhavans (Student hostels) of institute campus and

vegetable market (Sabzi mandi) of Rookee city. Grass cuttings (C/N=15), dry tree leaves

(C/N=120) and paper waste (C/N=250) collected from lawns and office premises of institute

campus. Sawdust (C/N=540) was purchased from nearby saw mill. The compost was

prepared with different proportioning of waste composition as described in experimental

design. Municipal solid waste was also collected from the temporary storage bins located in

civil lines area of Roorkee city. After manual sorting of plastics and other non-compostable

materials waste was ready for composting. Prior to composting, the maximum particle size

of the mixed waste was restricted to approximately 1 cm in order to provide better aeration

and moisture control. The material is rendered more susceptible to bacterial invasion

through exposing a greater surface area to attack and destroy the natural resistance of

vegetation to microbial invasion (Gotaas, 1956).

3.2 THE COMPOSTING REACTORS

3.2.1 BATCH OPERATION

Fig. 3.1 and 3.2 show a schematic diagram and pictorial views of a pilot-scale rotary

drum composter of 250 L capacity used for batch operation. The main unit of the

composter, i.e. the drum is of 0.92 m in length and 0.9 m in diameter, made up of a 4 mm

thick metal sheet. The inner side of the drum is covered with anti-corrosive coating. The

drum is mounted on four rubber rollers, attached to metal stand and the drum is rotated

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manually. In order to provide the appropriate mixing of wastes, 40 mm long angles are

welded longitudinally inside the drum. In addition, two adjacent holes are made on top of

the drum to drain excess water. Clockwise turning was carried out manually by handle,

which ensures proper mixing and aeration. Thereafter, aerobic condition was maintained by

opening half side doors. Two to three rotations at a time were made to ensure that the

material on the top portion moved to the central portion, where it was subjected to higher

temperature.

Fig. 3.1. Schematic diagram of rotary drum composter for batch operation

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Nylon roller

Dia = 0.9 m Length = 0.92 m

Revolving handle

Metal chain0.3 mm metal sheet

Front view Inside view

Feeding Waste within drum

Air Loading

Rollers


Fig. 3.2. Pictorial views of pilot-scale rotary drum composter

3.2.2 CONTINUOUS OPERATION

In order to study the continuous composting process, a full-scale rotary drum composter

of 3.5 m3 capacity was installed in institute campus (Fig. 3.3 and 3.4). The main unit of the

composter, i.e. the drum of 3.7 m in length and 1.1 m in diameter, made up of a 4 mm thick

metal sheet. The inner side of the drum was painted with anti-corrosive coating. The drum

is mounted on four metal rollers attached to metal stand. A 7.5 kW motor with gear reducer

is used to turn the drum in clockwise direction at a speed of 2 rpm. In order to provide the

appropriate mixing and agitation, 400 mm long angles with 4 mm width and 150 mm height

were welded longitudinally. These angles provided tumbling action and help to move the

waste material along the drum. With regards to the composting process, the main function

of rotation is to expose the material to air, add oxygen and release the heat and gaseous

products of decomposition. Two main openings are provided at both ends for waste inlet

and compost outlet. A 2.5 kW air blower fixed at the inlet end was used to suck the air from

outlet end for aeration. It also promoted the escape of water vapors and foul gases generated

during composting. Two ports are provided at the middle and outlet zone of drum to drain

possible excess water and to collect compost samples. The shredded mixed organic waste is

loaded into the drum by the means of plastic container on daily basis. To reach the

stabilization phase, the retention time was kept as 7 days. Two rotations at a time on daily

basis were made to ensure that the material on the top portion moved to the central portion,

where it will be subjected to higher temperature. Thereafter aerobic conditions were

maintained by opening the air blower.

Furthermore, the obtained primary stabilized compost was subjected to windrows and

vermicomposting for maturation.

Fig. 3.3. Schematic diagram of rotary drum composter for continuous operation

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Sampling ports

Dia = 1.1 m Length = 3.7 m

Speed = 2 rpm Unloading


Fig. 3.4. Pictorial views of full-scale rotary drum composter

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Side view Inside view

Front view Rear view

Composting shed Feeding into drum

Waste within drum Water Vapors after turning


3.3 EXPERIMENTAL DESIGN

In order to accomplish the objectives, the research was carried out in two attempts i.e.

Household batch composter and full-scale continuous operated composter. Each attempt

was divided into different phases as summarized in Fig. 3.5.

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Attempt 2Attempt 1Development of Rotary drum composters

Household Batch Composter(Performance evaluation)

Full-scale Continuous operated Composter

(Performance evaluation)

Phase 1-Different kind of waste combinations

[Mixture 1(C/N 16), Mixture 2 (C/N 22), Mixture 3 (C/N 30)]

Phase 2-Same kind of wastes combinations based on C/N

ratio(C/N 16, 22, 30, 38)

Selection of best combinations of wastes

Phase 3-Turning frequency

optimization (6 h, 12 h, 18 h, 24 h)

Utilization of MSW

Phase 4-Amendment of MSW (C/N>32) by Cattle manure (C/N 22) and Tree leaves (C/N 22)-Phase 4(Trial 1, Trial 2, Control)

Phase 5-Various combinations of MSW and Cattle manure-Phase 5

(1:0.67, 1:1, 1:1.5)

Optimal Operational mode

Phase 1-Start-up and waste combinations in different seasons

(Winter, spring, summer)

Phase 2-Maturation of drum compost in different seasons

using Windrows and Vermicomposting methods

(Run 1, Run 2, Run 3)

Optimal Operational mode


Fig. 3.5. Experimental design of the research work

3.3.1 BATCH OPERATION

As per the objectives of this thesis, the first attempt was to develop the pilot-scale rotary

drum for batch operation. The size of reactor explained earlier was decided on the basis of

the capacity of a single person, which can be easily handled by manual rotation and 60 to 70

kg of wastes. Initially all trials of different kind of wastes and their combinations were tried

on pilot-scale rotary drum. Later on experiments were tried for full-scale rotary drum

composter. The composting period of 20 days was decided for both active degradation

period and stabilization period based on the performance of earlier in-vessel composting

reactors. Initially two to three rotations were decided after every 24 hours.

The experimental work was carried out in five phases. The best combination of wastes

based on their chemical nature was decided in the first two phases. In the first phase,

composting was carried for three combinations of different kinds of wastes based on the

initial C/N ratios of 16 (mixture 1), 22 (mixture 2) and 30 (mixture 3). Grass cuttings,

mixed vegetable wastes and food waste were utilized for preparation of mixture 1. Mixture

2 contained cattle manure, mixed green vegetables and sawdust in a 2.5:2:1 ratio on wet

mass basis. Mixture 3 with C/N ratio of 30 was prepared by mixing cattle manure, mixed

green vegetables, food waste, paper waste and sawdust. Table 3.1 shows the proportion of

each waste in each mixture and physico-chemical parameters of mixtures on a dry matter

basis. In the second phase, composting was carried out for four combinations of same kind

of wastes based on the initial C/N ratios. Initial C/N ratios of 16, 22, 30 and 38 were

prepared using same kind of waste in different proportion including cattle manure, grass

cuttings, food waste, mixed green vegetables waste and saw dust. Table 3.2 shows the

proportion of each combination and physico-chemical parameters of each combination on a

dry matter basis.

The objective of the third phase was to evaluate the quality of compost under different

turning frequencies. The best performing combination during phase 1 (Mixture 2) was

chosen for the continuation of the experimentation to the third phase. Organic wastes

combination i.e. cattle manure, vegetable wastes/food waste and sawdust was taken into

account. Composting was stimulated by mixing/aeration of compost material by turning at

different time intervals i.e. 6 (Run A), 12 (Run B), 18 (Run C) and 24 hours (Run D) up to

15 days of composting. Experiments were focused on the effect of turning regime on

chemical composition of finished compost as well as the stability of compost by means of

rate of oxygen consumption and carbon dioxide evolution.

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Table 3.1: Waste composition and characteristics of three mixtures

Feedstock material (MSW composition) Mixture 1 Mixture 2 Mixture 3

Cattle manure (kg) 0 25 18

Grass cuttings (kg) 15 0 0

Food waste (Cooked) (kg) 10 0 25

Vegetable waste (Uncooked) (kg) 15 20 10

Paper waste (kg) 0 0 4

Saw dust (kg) 0 10 10

Manure (kg) 5 5 5

Total weight of mixture (kg) 45 60 69

Initial Moisture Content (%) 68.04 61.12 64.93

Initial pH 6.46 7.82 6.18

Initial electrical conductivity (dS/m) 5.41 2.52 3.21

Initial total organic carbon (%) 38.12 32.2 51.11

Initial ash content (%) 54.13 45.8 37.42

Initial total nitrogen (%) 2.37 1.42 1.67

Initial C/N ratio 16 22 30

Table 3.2: Waste proportion (weight basis)

Feedstock material (MSW composition) C/N 16 C/N 22 C/N 30 C/N 38

Cattle manure (kg) 5 10 16 22

Grass cuttings (kg) 8 6 4 2

Food waste (Cooked) (kg) 16 10 10 7

Vegetable waste (Uncooked) (kg) 30 20 20 18

Saw dust (kg) 0 2.7 7.5 10

Compost (kg) 5 5 5 5

Total weight of mixture (kg) 63 55.7 61.5 62

Initial Moisture content (%) 72.31 69.01 68.71 67.71

Initial pH 5.61 5.90 7.50 7.51

Initial electrical conductivity (dS/m) 5.11 4.41 4.31 4.80

Initial ash content (%) 48.51 53.01 49.11 41.81

Initial total organic carbon (%) 29.82 35.21 41.21 46.52

Initial total nitrogen (%) 1.91 1.51 1.30 1.22

Initial C/N ratio 16 22 30 38

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The aim of the fourth phase was to investigate the performance of pilot-scale rotary

drum during composting of both MSW (unamended control) and amended MSW with cattle

manure (trial 1) and tree leaves (trial 2) at an initial C/N ratio of 22. Table 3.3 shows the

physico-chemical parameters of unamended MSW and amended MSW on a dry matter

basis. Changes in physico-chemical and biological parameters including stability parameters

were analyzed for 20 days of composting period. In the fifth phase, study of composting

process of three different mixtures of MSW and cattle manure was carried out in a rotary

drum composter. The compost was prepared with three mixtures of municipal solid waste

(MSW) and cattle manure in 1:1.5 (Batch 1), 1:0.67 (Batch 2) and 1:1 (Batch 3) ratios, on

wet mass basis. Mixing proportion and physico-chemical parameters of mixtures on a dry

matter basis are detailed in Table 3.4.

Table 3.3: Waste composition and characteristics

Feedstock material Trial 1 Trial 2 Control

MSW (kg) 40 60 60

Cattle manure (kg) 30 - -

Tree leaves (kg) - 5 -

Compost (kg) 5 5 5


Initial Moisture content (%) 71.21 73.61 70.36




Initial C/N ratio 22 22 32

Table 3.4: Waste proportion of mixtures and physico-chemical characteristics

Feedstock material Batch 1 Batch 2 Batch 3

MSW (kg) 20 30 30

Cattle manure (kg) 30 20 30

Compost (kg) 5 5 5


Initial Moisture content (%) 76.81 76.12 79.53




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3.3.2 CONTINUOUS OPERATION

As per the objectives of this thesis, the second attempt was to develop a full-scale rotary

drum for continuous operation. The size of reactor as explained earlier was decided on the

basis of the amount of wastes required (maximum 120 kg/day) which can be easily

collected form various sources. Initially one rotation at the rate of 2 rpm and 10 min

aeration were decided before and after the feeding of wastes into drum. The experimental

work divided mainly into two phases. In the first phase, the main objective was to

monitoring of start-up conditions and performance evaluation for different waste

combinations. The effects of different waste combinations during ambient temperature (10-

30oC) on the outlet compost quality were monitored. The successful waste combination

during phase 1 of pilot-scale rotary drum was utilized for initial feeding into the drum. Later

on the waste combinations were changed according to the outlet and weathering condition

because the reactor started during winter season (Table 3.5 in Appendix). Mixing proportion

and physico-chemical parameters of initial mixtures on a dry matter basis are detailed in

Table 3.6. In the starting phase, cattle manure was used as inlet for the growth and

enhancement of the microbial activities. Afterwards, the main objective of utilization of

major components of MSW i.e. food/vegetable waste and tree/lawn waste was started.

Temperature and moisture content were observed on daily basis along with changes in

physico-chemical and biological parameters on alternate day basis in different seasons

including winter (0-70 days), spring (70-120 days) and summer (120-150 days). The results

of this study would be useful in defining operational guidelines and start-up conditions of

industrial-scale rotary drum composter dealing with different kind of organic wastes.

Table 3.6. Waste proportion and physico-chemical characteristics

Feedstock material Weight/Characteristics

Cattle manure (kg) 30

Mixed vegetable waste (kg) 50

Saw dust (kg) 7

Total weight of mixture (kg) 87

Initial Moisture content (%) 77.21

Initial ash content (%) 57.23

Initial total organic carbon (%) 35.36

Initial total nitrogen (%) 1.37

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In the second phase, a study was conducted to optimize the maturation process of

primary stabilized compost from rotary drum composter at ambient temperature by using

traditional composting, which was matured for a period of 20 days. The methods used for

maturation are as under:

Windrow composting (M1)

In this method of maturation, primary stabilized compost was formed into trapezoidal

piles (length 2100 mm, base width 350 mm, top width 100 mm and height 250 mm, having

length to base width (L/W) ratio of 6 as shown in Fig 3.6. Pile contained approximately 40

kg of primary stabilized compost and was manually turned on days 5, 10 and 15. The

maturation lasted total for 20 days.

Fig. 3.6. Maturation by windrow composting (L/W = 6)

Vermicomposting (M2)

Vermicomposting bed, each with an area of 0.25 m2 contained bedding material

comprising wheat straw, saw dust and matured compost (0.3 m deep) as shown in Fig 3.7.

Bedding was separated from primary stabilized compost using wire mesh which allowed

earthworm migration and beds were inoculated with Eisenia Foetida at the rate of 3 kg/m2.

Mean individual biomass for Eisenia Foetida was approximately 0.5-0.7 g. Primary

stabilized compost (approximately 5 kg) was applied to bed. Bed was covered and

maintained at approximately 60% moisture throughout. Physico-chemical and biological

analysis was performed on the mixed vermicomposted material collected from five random

locations within the bed.

The maturation study of primary stabilized compost was performed in three different

seasons, labeled as Run 1, Run 2 and Run 3. The details of the runs are tabulated in Table

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3.7. Initial physico-chemical and biological characteristics of primary stabilized composts

for Run 1, 2 and 3 are detailed in Table 3.8.

Fig. 3.7. View of Vermicomposting using Eisenia Foetida

Table 3.7. Detail of maturation study in different seasons

S. No. Season Month Ambient temperature (ºC) Label

1. Winter December 5-15 Run 1

2. Spring February 8-20 Run 2

3. Summer April 25-40 Run 3

Table 3.8. Initial characteristics of primary stabilized composts

Physico-chemical/Biological Characteristics Run 1 Run 2 Run 3


Initial Moisture Content (%) 73.51 74.02 73.01

Initial pH 8.39 8.38 8.74

Initial electrical conductivity (dS/m) 4.42 4.73 3.89


Initial C/N ratio 8.51 5.71 7.92

CO2 evolution (mg/g VS/day) 5.17 3.38 3.85

BOD (mg/L) 560 410 390

3.4 METHODS

Different experimental methods were used in the study to accomplish the stipulated

objectives. Physico-chemical and biological analysis of the samples collected from the

composters were carried out in different departments/centres of I.I.T. Roorkee, namly

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Environmental Engineering laboratory (Civil Engineering Departments), IA laboratory

(Chemical Engineering Department), AAS and TG laboratory (Institute Instrumentation

Centre), Instrumentation laboratory (Chemistry Department) and Central facilities

(Biotechnology Department). The flow chart demonstrates the patterns of physico-chemical

and biological analysis of collected samples (Fig. 3.8).

Fig. 3.8. Pattern of physico-chemical and biological analysis of samples

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Samples collection(Rotary drum & Initial waste)

Stored at 4oC

Wet samples Dry samples

Biological analysis

DW extraction

24 h in oven

Grinded and Sieved (0.2 mm)

Physico-chemical analysis

Bio-Degradability (BOD, COD)

Stability (CO2, OUR)

Coliforms(TC, FC, FS)

Pathogens(E. Coli,

Selmonella sp., Shigella sp.)

DW Extraction

Acid Extraction

PhysicalAnalysis(pH, EC,

WSOC, VFA)

NutrientsAnalysis(TN, TP,

Nutrients, Heavy metals

Ignition(TOC, Ash

content)

Spectroscopic(FTIR)

Thermal(DTA, TG)


3.4.1 SAMPLING

About 100 g of each grab samples were collected from six different locations, mostly at

the mid span and end terminal s of the pilot-scale rotary drum composter by compost

sampler without disturbing the adjacent materials. Finally all the grab samples were mixed

together and considered as homogenized sample. Samples were collected on day 1, 3, 5, 8,

10, 12, 15, 17 and 20 of the composting process. Triplicates homogenized samples were

collected and stored for maximum 2 days at 4oC immediately for biological analysis. Three

grab samples from inlet, middle and outlet ports were collected from full-scale rotary drum

composter every alternate day. The samples from the windrows and vermicomposting beds

were collected at every fifth day of maturation period (5, 10, 15 and 20 days). Wet samples

were used for biological analysis after properly mixing. Sub-samples were air dried

immediately, ground to pass through 0.2-mm sieve and stored for further analysis. Each

sub-sample was analyzed for the physico-chemical parameters.

3.4.2 PHYSICO-CHEMICAL ANALYSIS

Temperature

Temperature was monitored on the basis of 6 hour time interval using a digital

thermometer throughout the composting period within pilot-scale rotary drum composter.

During full-scale rotary drum composting, temperature readings were taken directly using

handheld analog thermometer, inserted into the composting mass in three different locations

at 24 hour time interval.

Moisture content

Moisture content was determined by weight loss of compost sample (105oC for 24 hour)

using the gravimetric method (BIS, 1982).

pH and electrical conductivity (EC)

Stirred 5 g of the sub-sample in 50 ml distilled water and pH was measured using a pH

meter with a glass electrode, previously calibrated and corrected for temperature (BIS,

1982). Filtrate of the above mixture by Watman filter paper No. 42 and was used to

measuse the EC using a conductivity meter.

Total Organic Carbon (TOC) and Ash content

About 250 mg of sub-sample used for determination of TOC by Shimadzu (TOC-VCSN)

Solid Sample Module (SSM-5000A). Ash content was measured by the ignition method

(550oC for 2 hour in muffle furnace) (BIS, 1982). Decomposition (Dec) was calculated

according to the following formula (Jouraiphy et al., 2005):

Dec (%) = 100 × [(Af-Ai)/Af × (100-Ci)] × 100,

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Where Af is final ash content (in fraction), Ai is initial ash content (in fraction) and C i is

initial TOC (in fraction).

Total nitrogen (TN), ammonical nitrogen (NH4-N) and Nitrate (NO3-N)

100 ml samples were prepared for analyzing TN using Kjeldahl method and HACH

TKN kit by acid digestion of 0.5 g of sub-samples in 4 ml of conc. H2SO4 in the presence of

10-15 ml of 30% H2O2. KCl (30 ml of 0.2 M KCl) extraction of 3 g of each sub-sample was

used for the analysis of NH4-N and NO3-N using Standard methods (Tiquia, 2000; APHA,

1995).

Nutrients and trace elements

100 ml samples were prepared for analyzing nutrients including (total phosphorus,

potassium, sodium and calcium) and trace elements including Cr, Ni, Fe, Cd, Pb, Zn and Cu

by acid digestion of 0.5 g of sub-samples in 2 ml of each conc. HNO3 and conc. HCl in

presence of 10 ml of 30% H2O2. Total phosphorus (TP) was analyzed using stannous

chloride method (APHA, 1995). Potassium, sodium and calcium were determined using

flame photometry. Trace elements were analyzed using Atomic Absorption Spectroscopy

(APHA, 1995).

Water- soluble organic carbon (WSOC) and Volatile fatty acids (VFAs)

Ten grams of each sub-sample was weighted into a 250 ml polycarbonate centrifuge

tube and extracted with 100 ml of deionized water by shaking for 24 hours. The extracts

were centrifuged at 8000 rpm for 20 min and filtered through 0.45 µm filter membranes.

Water extracts were stored at 4oC for analysis of water-soluble organic carbon using

Shimadzu TOC-5000A (Huang et al., 2006). The presence of VFAs (water soluble)

including acetic acid, formic acid, butyric acid, propionic acid was determined in the same

prepared samples using Hewlett-Packard (HP) Liquid Chromatograph accomplished with

UV detector (Column: NovaPac 39 mm O.D. × 150 mm length).

Fourier-transform infrared (FTIR) spectroscopy

The FTIR spectra were obtained on wave number range of 400-4000 cm -1 on a Perkin

Elmer GX FT-IR system equipped with OMNIC software. The sub-samples (1, 7, 15 and 20

days) were prepared for analysis by mixing 1 g of dried KBr with approximately 7-10 mg of

sub-sample and compressing the mixture to pellets.

Thermal analysis

Four samples (1, 7, 15 and 20 days) were selected from a sample set of 9 samples

collected during the composting process for thermal analysis. Thermogravimetry (TG) and

Derivatives thermogravimetry (DTG) were carried out with a Mettler TG20 Termobalance,

TA 3000 system. A calibration with trafoperm, nickel and isotherm contemporarily,

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followed by a check with nickel, was performed before the analysis. The following

conditions were adopted for all TG and DTG analyses: heating rate of 10oC/min from 25 to

800oC, oxidizing atmosphere for static air, and sub-samples weights of about 10 mg.

Differential thermal analysis (DTA) was carried out with a Mettler TA-STAR 821. A total

calibration with indium/zinc, followed by a check DTA exo-indium, was performed before

the analysis. The following conditions were adopted for DTA analyses: heating rate of

5oC/min from 45 to 550oC, oxidizing atmosphere for static air, and sub-samples weights of

about 10 mg. Measurements were repeated at least three times.

3.4.3 BIOLOGICAL ANALYSIS

Each homogenized sample (wet sample) was analyzed three times for the following

parameters.

Coliform analysis

Supernatant of the blended mixture of 10 g samples in 100 ml deionized water was

tested for bacterial population including total coliforms (TC), fecal streptococci (FS) and

fecal coliforms (FC) by inoculation of culture tube medias with Lauryl tryptose broth, Azide

dextrose broth and EC medium respectively using the Most Probable Number (MPN)

method (APHA, 1995).

BOD and COD

The biodegradable organic matter was measured as biochemical oxygen demand (BOD)

(by the dilution method, APHA, 1995), chemical oxygen demand (COD) (by the

dichromate method, APHA, 1995) of supernatant of the blended mixture of 10 g sample in

100 ml deionized water.

Oxygen uptake rate (OUR)

The oxygen uptake rate (OUR) was performed according to the method describe by

APHA (1995). The OUR was measured on a liquid suspension of compost (8 g of compost

in 500 ml of distilled water added with CaCl2, MgSO4, FeCl3 and phosphate buffer at pH

7.2, made up according to the standard methods BOD test procedures (APHA, 1995))

incubated at room temperature (24±2oC). The DO probe was placed in the sample bottle, its

sensor being at a depth of 5–7 cm below the water surface. The suspension was

continuously stirred by means of a magnetic stirrer. The O2 concentration was measured

continuously and this value quoted as the OUR in mg O2/g VS/day.

CO2 evolution

Microbial respiration of compost samples, based on CO2 evolution was measured using

static measurement method (Knoepp and Vose, 2002). Approximately, 10 g of sample was

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sealed in a 0.5 L vessel along with a beaker containing a known weight of oven dried

(105oC) soda lime (1.5–2.0 mesh). The samples were incubated at room temperature

(24±2oC). Blank necessary for trap CO2 calculation described as above without putting a

sample in a vessel. Soda lime trap were removed after 24 hour, oven dried and reweighed to

determine CO2 absorbed. Finally, the CO2 test values and OUR were used to determine the

Solvita® maturity index on a scale of 1–8 which then represent the maturity level of the

compost samples.

Another method suggested by Strotmann et al. (2004) based on the direct relationship

between CO2 production and change of conductivity in a well specified, calibration system

used for CO2 evolution (Fig. 3.9). He concluded, this test fulfilled the requirements of

standardized biodegradation tests and may serve as a basis for further development

biodegradation tests in different areas. Approximately, 40 g of sample was sealed in a 0.5 L

vessel along with a beaker containing a known volume of (50 mL) 0.25M KOH solution.

The samples were incubated at room temperature (24±2oC). Here, CO2 was trapped and

measured by change in conductivity after 24 hours of incubation. The absorption solution

was continuously stirred with a magnetic bar. After conversion of the measured

conductivity (millisiemens per centimeter) to CO2 (milligram per liter) and subtracting

blank value, biodegradation was calculated. There was a linear correlation between the

amount of CO2 liberated and the change in conductivity.

Fig. 3.9. Relationship between conductivity and CO2 evolution (Strotmann et al., 2004)

Pathogens (Salmonella sp., Shigella sp. and E. coli)

Salmonella concentrations during composting were determined by using a standard five

tube most probable number (MPN) method using tryptic soy broth with plating mediums of 52


Modified Semisolid Rappaport Vassiliais (MSRV) medium and Xylose Lysine

Deoxycholate (XLD) agar, TSI and LIA agars (For biochemical confirmation) ((Himedia,

Bombay) (EPA, 2005a). For isolation of Shigella, plating medium of low selectivity such as

MacConkey agar (MaC) (Himedia, Bombay) was used along with enrichment material of

Shigella broth (FDA/CFSAN, 2001). E. coli was enumerated by membrane filtration (0.45

µm) (EPA, 2005b) using mTEC agar (Himedia, Bombay) as the plating media.

3.4.4 STATISTICAL ANALYSIS

All the results reported are the means of three replicates. One-way, two-way analysis

and repeated measures treated with ANOVA (Analysis of variances) were made using

Statistica software, Statsdirect software and SPSS package. The objective of statistical

analysis is to determine any significant differences among the parameters analyzed during

the composting process

3.5 INSTRUMENTS AND EQUIPMENTS USED

Instruments required for physico-chemical and biological analysis of solid wastes and

composts are detailed in table 3.9-3.11.

Table 3.9. Instruments used for physico-chemical analysis

Parameter Instrument/Equipment Model/Manufacturer/Specification

Moisture content Hot air oven TempStar

pH Digital pH meter Toshniwal Instrument Manufacturing

Pvt. Ltd. India.

EC Conductivity benchtop Orion 4 star, Thermo Electron

Corporation

TOC TOC-VCSN Shimadzu, Solid Sample Module,

SSM-5000A.

Ash content Muffle furnace NSW India.

TN Vapokjel & Thermokjel Jaguar DS 30, Jaguar Instrument

Technology

NH4+-N Spectrophotometer DR/4000, HACH, USA

NO3--N Spectrophotometer DR/4000, HACH, USA

TP Spectrophotometer DR/4000, HACH, USA

K, Ca, Na Flame photometer Model, TMF-45, Toshniwal, India.

Trace elements Atomic Absorption Spectroscopy GBC Avanta Ver 1.31

WSOC TOC-VCSN Shimadzu, SSM-5000A

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VFAsHewlett-Packard (HP) Liquid

Chromatograph

UV detector, column (NovaPac 39

mm O.D. × 150 mm length)

FTIR Thermo Nicolet FT-IR Nexus system operated with OMNIC

software

Thermal analysis Perkin Elmer Pyris Diamond Mettler TA-STAR 821

Table 3.10. Instruments used for biological analysis

Parameter Instrument/Equipment Model/Manufacturer/Specification

BOD BOD incubator Digital TempCon DTC-201

COD COD analysis system HACH COD reactor model

DR/4000, USA.

Coliform Incubators and Laminar flow

supply hood

TempStar

E.coli Membrane filtration Assembly Borosil, India.

Salmonella Test tubes and Petri plates Borosil, India.

Shigella Test tubes and Petri plates Borosil, India.

OUR UC-12, Digital DO meter Central Kagaku Corporation, Japan

CO2 evolution Incubator TempStar

Table 3.11. Other instruments and accessories used for analysis

Instrument/Equipment Purpose Model/Manufacturer/Specification

Shaker Shaking/Blending Sara Instruments, Roorkee (India)

Oven Drying TempStar

Fume Hood Digestion chamber ST 1200 ABP, G LAB

Heater Digestion Q-5247, Navyug, India

Grinder Grinding Sumeet, India

Sieves Sieving Unique Drawing & Survey Emporium,

Roorkee (India)

Hand gloves and Apron Hand precaution Safety purpose

Pipettes Volume measurements Qualigens Ltd.

Balance Weighing Mettler Tolido, AG 285

Centrifuge Centrifuge Research centrifuge, REMI, India

Glassware Analysis and storage Borosil, India

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chapter 3_material & method

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