mechanism of phosphorus removal by sbr

8/4/2019 Mechanism of Phosphorus Removal by Sbr

1/6

MECHANISM OF PHOSPHORUS REMOVAL BY SBR

SUBMERGED BIOFILM SYSTEM

BAOZHEN WANG**M, JUN LI, LIN WANG*M , MEISHENG NIE and JI LI

Water Pollution Control Research Center, Harbin University of Architecture and Engineering,66 West Dazhi Street, Harbin 150006, PR China

(First received January 1997; accepted in revised form September 1997)

AbstractThe mechanism of phosphorus removal in SBR submerged biolm system was studied in theresearch. The DNP and nuclear magnetic resonance methods were employed to verify the mechanismof phosphorus removal by bacteria with the phosphorus release in anaerobic phase and uptake in oxic

and anoxic phases. The mathematical models of phosphorus releases in anaerobic phase and phos-phorus uptake in oxic phase were deduced and evaluated by comparison between the theoretically cal-culated values and the test data. # 1998 Elsevier Science Ltd. All rights reserved

Key wordssequencing batch reactor, submerged biolm system, biological phosphorus removal,phosphorus release, phosphorus uptake

INTRODUCTION

It has been well proved by many researches that the

submerged biolm systems including those with

xed and suspended carriers like Lindpor processes

(Morper and Wildmoser, 1990; Morper, 1994) are

very eective and ecient in organic and nitrogen

removal by means of the attached growth biolm,which exhibits lots of advantages as compared with

activated sludge process such as stability and long

retention time of microorganisms, much higher bio-

mass content in terms of MLSS and MLVSS, much

less surplus biomass or sludge because of longer

food chains exist in biolm consisting of abundant

amount and various species of metozoa, protozoa,

bacteria and fungi (Wang et al., 1991). However,

the continuous ow submerged biolm systems have

been proved by many studies to be only ecient in

nitrogen removal, the ammonia removal by nitrica-

tion in particular (Wang et al., 1991, 1992; Lee and

Welander, 1994; Liu and Capdeville, 1994; Mik etal., 1995), but not ecient to remove phosphorus,

which is mainly due to the uneven distribution of bio-

mass either in quantity or in microbial species along

the ow path in the continuous ow submerged bio-

lm reactor (CFSBR), which are usually divided into

two sections, i.e. anoxic and oxic (A/O) zones, in

which the microbial community is dominated by het-

erotrophic species of bacteria responsible for organic

degradation and denitrication in anoxic zone and

the autotrophic nitrifying bacteria are dominant

species for nitrication in oxic zone. In the A/O sub-

merged biolm system there is no room for P

removal or accumulating bacteria growth because

there exists no alternative anaerobic/oxic environ-

mental conditions for their growth, which is hardly

developed in the CFSBF. However, the submerged

biolm sequencing batch reactor (SB-SBR) that oper-

ates with an alternate anaerobic/oxic procedure devel-

oped by the authors have been proved very ecient in

phosphorus removal (Li, 1996). Two methods were

employed in the study to verify the biological removal

of phosphorus, of which the 2,4 dinitrophenol (DNP)

was added as a xenobiotic to observe its inhibitory

eect on biological P removal and the 31P nuclear

magnetic resonance spectroscopic technique (Hill et

al., 1989) was used to verify the phosphorus release

and uptake biologically in anaerobic, oxic and anoxic

phases, respectively, by observation of the variation of

peaks of ortho-phosphate and polyphosphate in the31P NMR spectrograms under anaerobic, anoxic and

oxic conditions. Some mathematical models for simu-

lating phosphorus release in the anaerobic phase and

phosphorus uptake in the oxic phase have been

developed as well.

EXPERIMENTAL METHOD

Experimental equipment

As shown in Fig. 1, the experimental equipment wasmade of a plexiglass column with an inner diameter of15 cm and a volume of 22 l, of which the eective volumewas 16 l, in which the biolm carriers occupied 6 l and thesettling zone 2 l.

Test process, parameters and synthetic wastewater

The test process was employed as follows: Inuent 4anaerobic phase, with HRT of 3 h 4 oxic phase, 6 h 4sedimentation, 1 h. The raw wastewater was prepared by

the mixing of a certain amount of peptone, ammoniachloride magnesium sulfate, calcium chloride and sodiumchloride and potassium dihydrogen phosphate. The main

Wat. Res. Vol. 32, No. 9, pp. 26332638, 1998# 1998 Elsevier Science Ltd. All rights reserved

Printed in Great Britain0043-1354/98 $19.00 + 0.00PII: S0043-1354(97)00413-2

*Author to whom all correspondence should be addressed.

2633


2/6

Fig. 1. Schematic diagram of experimental equipment.

Fig. 2. Eect of DNT on P release in anaerobic phase andP uptake in oxic phase.

Table 1. The synthetic wastewater quality

Parameter Concentration (mg/l)

COD 250400BOD5 180300TN 3060NH4

+ N 1020

NO3 N 0.2

NO2_N 0.1

TP 10

SP 8pH 7.3 (log[H

+]1

)Alkalinity 380440

quality parameters of the synthetic wastewater are shown inTable 1.

Tests and results

Addition of DNP. 20 mg/l DNP (2,4 dinitrophenol) wasadded to the raw wastewater and the submerged biolmSBR was operated according to the alternate A/O pro-cedure as mentioned in Section 1. The result is shown inFig. 2. The phosphorus release was still observed in theanaerobic phase, but the phosphorus uptake was notobserved in the oxic phase, which indicated that DNP is adecoupling agent that inhibits phosphorylation respiratory

chains and ATP formation, thus preventing phosphorusaccumulation in the oxic phase, but does not aect thephosphorylation beside the oxidation respiratory chain. Inthe metabolism process of polyphosphate decompositionin the anaerobic phase, the ATP is produced by phos-phorylation at the substrate level which was not inhibitedby DNP, thus causing PO4

3 release and PHB formation,However, in the oxic phase in the presence of oxygen theATP was not formed due to the inhibition to electrontransfer in the respiratory process, which led to no phos-phorus uptake and polyphosphate formation and thereforeno phosphorus removal in the oxic phase because of theDNP inhibitory eect.

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPIC

TECHNIQUE

Test method

Material. Bacteria strains used in the test were

contained in the biolm taken from the carrier in

the submerged biolm SBR for phosphorus removal,

which were cultured by many times of alternate A/O

operation, thus resulting in the maturation of the P-

removing bacteria strains. The biolm containing the

bacteria strains was diluted with NO3 free distilled

water with the addition of beef paste as culture med-

ium to a nal solution with BOD5 of 600 mg/l.

Test equipment. An AC 80 type nuclear magnetic

resonance spectrometer produced by Brucrer Co. in

Switzerland was employed for analysis at 36.43 Mhz.

A few drops of D2O and then HMPA (hexamethyl

phosphoramide) were added onto the culture med-ium, which exhibited a peak at +25 ppm and served

as an external standard of phosphorous compounds

in biomass.

The scanning range was 6000 Hz, the capture time

was 0.17 s, the pulse was 808, decay was the multi-

plicity of the exponential function of 6 Hz, the ac-

cumulative rotation number was from 10,000 r

to 20,000 r, the temperature was 278C, chemical

Baozhen Wang et al.2634


3/6

position moving unit ppm, 85% ortho-phosphate

was used as reference sample. The removed biolm

of 3000 mg after 5 min of centrifugal separation was

put into a 10 ml sample tube.

Results and discussion. The variation of spectral

peaks in the anaerobic phase are shown in Fig. 3.

At the beginning of the anaerobic phase there

existed three peaks, of which the peak at +25 ppm

was caused by HMPA, the peak at +2 ppm by

PO43 and that at 22 ppm by polyphosphate. Thepeaks varied with operating time in the anaerobic

phase with such a typical tendency that the peak at

22 ppm decreased gradually with the decrease of

polyphosphate content until the peak disappeared

after a 28 h operation, which indicated that the

polyphosphate contained in the bacterial cells was

decomposed into phosphate. The peak at +2 ppm

increased gradually with the increase of ortho-phos-

phate content from the degradation of polypho-

sphate, which took place completely after a 28 h

operation in the anaerobic phase as clearly shown

in Fig. 3.

The variation of the 31P-NMP spectrogram in theanaerobic/oxic phases in turn is shown in Fig. 4.

The three spectrograms express the original state of

biolm at the beginning of the anaerobic phase,

after a 5 h operation in the anaerobic phase and the

state after 5 h aeration in the oxic phase, respect-

ively, from which it was found that the peak of

ortho-phosphate at +2 ppm increased signicantly

in a 5 h operation in the anaerobic phase than that

at beginning, but decreased sharply in the oxic

phase and dropped to a very small peak after 5 h

aeration, while the peak of polyphosphate at

22 ppm increased sharply, which clearly indicated

that the biolm took up phosphate and carried outthe polyphosphorylation, which resulted in the

decrease of ortho-phosphate content and the

increase of polyphosphate content in biolm under

oxic conditions.

As shown in Fig. 5, under anoxic conditions, the

inorganic phosphorus was also converted to poly-

phosphate with the NO3 as oxygen source, which

indicated that the uptake and polyphosphorylation

of inorganic phosphorus could take place in bac-

terial cells under anoxic conditions as it did under

oxic conditions but with NO3 as oxygen source,

which is similar to another study carried out in anactivated sludge system with biolm nitrication

(Sorm et al., 1996)

It has been concluded from the study of 31P-

NMR spectrograms of biolm under anaerobic,

oxic and anoxic conditions that the P-removing

bacteria contained in submerged biolm released

phosphorus due to the degradation of polypho-

sphate into ortho-phosphate under anaerobic

Fig. 3. 31P-NMP spectrogram of biolm in anaerobicphase.

Fig. 4. 31P-NMR spectrogram of biolm in anaerobic/oxicphase.

Fig. 5. 31P-NMP spectrogram of biolm in anoxic/oxicphases.

Mechanism of phosphorus removal by SBR 2635


4/6

conditions and took up phosphorus and carried

out polyphosphorylation under oxic and anoxic

conditions.

MATHEMATICAL MODELS ON PHOSPHORUS REMOVAL

IN AN SBR SUBMERGED BIOFILM SYSTEM

Dynamic model development

Phosphorus release in anaerobic phase. Two deci-

sive factors aecting the concentration distribution

in biolm are mass transfer rate and reaction rate,

which were also aected by the concentration distri-

bution, Therefore, the rst order reaction equation

was employed to describe the phosphorus release

and organic uptake in anaerobic phase as follows:

dPadt K1Pm P 1

dLadt K2L Lm 2

in which Pm is the maximum value of phosphorus

release, mg/l; P is the instant value of phosphorus

concentration in biolm SBR at time t, mg/l; K1 is

the phosphorus release rate constant, h1; dP/dt is

the phosphorus release rate, mg/lh; dL/dt is the

substrate uptake rate, mg/lh; Lm is the nal value

of substrate, mg/l; L is the instant value of sub-

strate concentration at time t in biolm SBR and

K2 is the substrate uptake rate constant, h1.

The values of Pm and Lm were determined by

test. Equations (1) and (2) are integrated to achieve

the time functions of P and L as follows:

P Pm Pm P0expK1t 3

L Lm Lm L0expK2t 4

in which PmP0=DPm: maximum probable amount

of phosphorus release, mg/l; LmL0=DLm: maxi-

mum probable amount of COD removal, mg/l; P0:

initial TP concentration, mg/l; L0: initial COD con-

centration, mg/l.

In order to achieve the amounts of phosphorus

release and organic uptake at any time, two vari-

ables were dened as follows:

P H P P0 5

L H L L0 6

in which P' is the TP release at time t, mg/l; L' is

the COD removal at time t, mg/l.

Substituting equations (5) and (6) into

equations (3) and (4), the following equations are

obtained:

P H DPm1 expK1t 7

L H DLm1 expK2t 8

which after simplication, achieve

expK1t DPm PHaDPm 9

expK2t DLm LHaDLm 10

which after processing logarithmically become

K1t lnD

Pm P

H

aD

Pm 11

K2t lnDLm LHaLm 12

equation 11 is divided by equation 12 and then sim-

plied, thus obtaining the following equations:

P H DPm1 1 LHaDLm

K1aK2 13

PaDPm 1 1 LHaDLm

K1aK2 14

Estimation of parameters of the models

The peptone was used as a substrate, inuent

COD was 340380 mg/l, TP was 9.510.0 mg/l, the

total HRT in the reactor was 9 h, of which the an-aerobic phase took 3 h and the oxic phase 6 h and

the temperature was maintained at 208C, at which

the average values of DLm and DPm were obtained

as 175.0 and 4.05 mg/l, respectively, by test.

The estimation of parameters was carried out by

computer scanning calculation-gradient search

method (Li and Wang, 1989), by which the phos-

phorus release rate constant was obtained from

equations (3) and (4) as K1=0.750 h1 and the or-

ganic uptake rate constant as K2=0.910 h1.

In order to verify the correctness of the devel-

oped models, the track test values are used to make

comparisons between the theoretically calculatedand test values, which are shown in Figs 68, from

which it is evident that the calculated values from

the developed equations coincide with correspond-

ing test values very well, which indicates that

equations (3)(5) can describe phosphorus release

and COD removal satisfactorily under anaerobic

conditions in submerged biolm SBR.

Phosphorus uptake in oxic phase

Similar to organic uptake in the anaerobic phase,

the organic degradation in the oxic phase can be

Fig. 6. Comparison between the test and calculated valuesof phosphorus release at three COD loading rates.



5/6

also described as follows:

dLadt K3L Le 15

in which K3 is the organic degradation rate con-

stant, h1 and Le is the euent organic concen-

tration measured by COD in the oxic phase, which

was determined by test and can be regarded as non-

degradable COD. After integration equation 15 is

converted into the following equation:

L Le L0 LeeK3T 16

in which L0 is the inuent organic (COD) concen-

tration, mg/l.

A track test was carried out by using peptone asa substrate, from which the euent COD value in

the oxic phase was determined as 38.0 mg/l.

The parameter was also estimated by the compu-

ter scanning calculation-gradient search method and

the organic degradation rate constant was obtained

as K3=1.300 h1, which was much higher than that

of organic uptake. K2=0.90 h1 in the anaerobic

phase. The theoretically calculated values expressed

in a curve and the test values expressed in circular

points are shown in Fig. 9.

The eect of three dierent substrates such as

peptone, glucose and acetic acid on the value of the

organic degradation rate constant was studied as

well and the results are shown in Table 2, whichshows that the K3 values of glucose and acetic acid

are remarkably higher than that of peptone, which

means that the microorganisms rst utilize the more

readily degradable organic compounds with smaller

molecular weight.

The correlation between phosphorus release in

the anaerobic phase and phosphorus uptake in the

oxic phase was also researched with the results

shown in Fig. 10, which clearly indicated that the

maximum P uptake, DPm, in the oxic phase was

proportional to the maximum P release in the an-

aerobic phase, from which after linear regression

processing, the following equation was derived:

DPm oxic 0X93P anaerobic 9X24 mgal 17

with a correlation coecient of 0.94.

The maximum anaerobic P release and aerobic P

uptake values with three dierent substrates are

shown in Table 3. As a result, the theoretically cal-

culated values of P release and uptake rate con-

stants and organic removal rate constant coincided

with respective test ones very well.

CONCLUSION

The 2.4 dinitrophenol (DNP) which has the

characteristics does not inhibit phosphorus release

in the anaerobic phase but does inhibit phosphorus

uptake in the oxic phase, was employed to verify

that the phosphorus was removed biologically in

the submerged biolm SBR.31P-NMR spectrograms were used to explain the

mechanism of phosphorus removal, from which the

polyphosphate was decomposed and converted into

Fig. 7. Comparison between the test and calculated valueof COD removal at three COD loading rates.

Fig. 8. Correlation between phosphorus release and CODuptake.

Fig. 9. Comparison between theoretical and test values oforganic removal in anaerobic and oxic phases.

Table 2. COD removal rate constant values with three dierentsubstrates

Substrate L0 (mg/l) Le( mg/l) K3 (h1

)

Peptone 192.9 38.0 1.300Glucose 180.0 25.2 1.560Acetic acid 195.2 22.6 1.520

Mechanism of phosphorus removal by SBR 2637


6/6

inorganic phosphorus in the form of ortho-phos-

phate in the anaerobic phase and the inorganic

phosphorus was converted to polyphosphate and

storage in bacterial cells in the oxic and anoxic

phases.

Mathematical models have been developed on P

release in the anaerobic phase and P uptake in the

oxic or anoxic phase, in which the optimum values

of parameters were calculated by the computer

scanning calculation and gradient search method,

by which the calculated values of P release and

uptake and organic removal coincide with the

respective test ones very well.

REFERENCES

Hill W. E., Beneeld L. D. and Jing S. R. (1989) 31-NMR Spectroscopy characterization of polyphosphatesin activated sludge exhibiting enhanced phosphorusremoval. Water Res. 23(9), 11771181.

Lee N. M. and Welander T. (1994) Inuence of predatorson nitrication in oxic biolm processes. Water Sci.Technol. 29(7), 355363.

Li J. and Wang B. Z. (1989) Pollution control of HutuoRiver with mathematical modeling. River BasinManagement. In Advance in Water Pollution Control,pp. 147158. Pergamon Press, Oxford.

Liu Y. and Capdeville B. (1994) Dynamics of nitrifyingbiolm growth in biological nitrogen removal process.Water Sci. Technol. 29(7), 377380.

Mik T., Mattsson A., Nanasson E. and NiklassonC. (1995) Nitrication in a tertiary trickling lter athigh hydraulic loads-pilot plant operation and math-ematical modeling. Water Sci. Technol. 32(8), 185192.

Morper M. R. and Wildmoser A. (1990) Improvement ofexisting wastewater treatment plant eciencies withoutenlargement of tankage by application of the lindporprocess, case studies. Water. Sci. Technol. 22(718), 207215.

Morper M. R. (1994) Full scale application of specializedbiological processes for advanced wastewater treatment.Proc. of Int. Conf. on Water and Waste Water, pp. 661669. Beijing.

Li J. (1996) Phosphorus and nitrogen removal by SBRsubmerged biolm process. Doctoral thesis, Dept. ofMunicipal and Environmental Engineering, Harbin

University of Architecture and Engineering (inChinese).

Sorm R., Bortone G., Saltarelli, Jenieek P., Warner J. andTilche A. (1996) Phosphorus uptake under anaerobiccondition and xed-lm nitrication in nutrient removalactivated sludge system. Water Sci. Technol. 30(7),15781584.

Wang B., Li G., Yang Q. and Liu R. (1992) Nitrogenremoval by a submerged biolm process with brouscarriers. Water Sci. Technol. 26(911), 20372089.

Wang B., Yang Q., Liu R., Yuan J., Ma F., He J. and LiG. (1991) A study on simultaneous organic and nitro-gen removal by extended aeration submerged biolmprocess. Water Sci. Technol. 24(5), 197213.

Fig. 10. Correlation between the anaerobic P release andaerobic P uptake with peptone as organic substrate.

Table 3. Maximum anaerobic P release and aerobic P uptakevalues, DPm (mg/l)

Substrate In. TP In. CODAnaerobic

DPm Oxic DPm

Peptone 9.3 102.0 0.8 9.19.6 272.7 1.6 10.3

10.2 372.0 4.0 13.59.1 649.8 4.7 13.6

11.1 942.1 5.2 16.3

Glucose 8.0 427.0 7.5 15.3

Ethanoic acid 8.2 395.7 10.4 18.4


mechanism of phosphorus removal by sbr

Documents