8) Pergamon

PH: S0273-1223(98)00479-X

War. Sci. Tech. Vol. 38, No.2, pp. 177-184, 1998.IAWQ

<Cl 1998 Published by Elsevier Science Ltd,Printed in Great Britain. All rights reserved

0273-1223198 $19'00 + 0'00

DYNAMICS OF METHANOGENICACTIVITIES IN A LANDFILL BIOREACTORTREATING THE ORGANIC FRACTION OFMUNICIPAL SOLID WASTES

J.1. Lay*'**, Y. Y. Li*** and T. Noike*

*Department ofCivil Engineering, Faculty ofEngineering, Tohoku University. Aoba.Sendai 980-77, Japan**CREST, Japan Science and Technology Corporation (JST)*** Technical Research Institute, Ataka Construction & Engineering Co. Ltd, 2-11.Funamachi 2-chome. Taisyo-ku, Osaka 551. Japan

ABSTRACT

A bench-scale Investigation was conductedto evaluate the dynamicsof methanogenic activities in a landfillbioreactor(LFBR)ueatlng the organicfraction of municipal solidwastes(OFMSW). The specificmethanogenicactivity (SMA) test was used to measureeach Individual methanogenic activity on degrading carbohydrate.protein, lipid, butyrate.propionate. and acetateat an Interval of one-year. A simplemodel incorporating threebiokineticparameters. namely lag-phasetime.methane production rate and methaneproductionpotential.wasemployedto systematically describe thedynamics of SMAon theanaerobic mineralization of the OFMSWin anLFBR. The results indicatethat the modelis suitableto describe thedynamics of SMAin theLFBR. Accordingto the dynamicsof the SMA, the decomposition of proteinsand lipidsoverruledthe stabilization of the LFBR.while the rate of methanogenesis was higher than that of acetogenesis. Comparing the estimation and theobservationof methane productionrates suggestedthat the period of the critical Incubation time (A*) of theproteinand the lipidinfluenced theeffICiency of theLFBR. © 1998 Published by ElsevierScienceLtd.All rightsreserved

KEYWORDS

Landfill bioreactor; methanogenesis; organic fraction of municipal solidwaste; specific methanogenic activity

INTRODUCTION

Anaerobic digestion of organic solid waste, especially the OFMSW, is of growing importance in the field ofsolid-waste management The useof leachate containment, collection andrecirculation on a landfill hasprovidedopportunity to transfer a landfill into a controlled bioreactor system. Several types of bioreactors have beendeveloped for the treatment of an OFMSW, including continuous and batchdigesters. A batchdigester, such asa landftllbioreactor, treating the OFMSW is in essence simplerthan a continuous anaerobic digester, and thelowercost per ton of waste treated in a landfill reactoris a consequence of the simple technology applied (tenBrummeler andKoster, 1990; Pohland, 1996). Compared withconventional sanitary landfills, landfill bioreactorsprovide the potential for more rapid,complete and predictable attenuation of solid waste constituents, enhancegas recovery and utilization, and reduction in health/adverse environmental impacts and attendant liabilities(Pohland, 1997).

Characteristics of methane fennentation of organic refuse samples strongly dependon its chemicalnature(Layet al., 1996a; Layet al., 1997a). Understanding and recognizing the methane fermentation characteristics of anOFMSW in a landfill bioreactorare, therefore, increasingly important for reducing the pollution potential andenhancing the methane production of OFMSW (Rivard et al., 1989; Mormile et at, 1996). Manyattempts havemade to enumerate bacterial populations and measure enzyme activity of the bacteria during organic refusedecomposition (Rees, 1980;Iones and Grainger, 1983; Barlaz, 1989). However, to date no attempt has beenmade to fonnulate a modeldescribing the dynamics of methanogenic activity by the quantitative measurement of

117

178 J. J. LAY etal.

the substrate utilization on a LFBR treating an OFMSW.

The objective of this study was to examine the dynamics of methanogenic activities during methane fermentationof the OFMSW. For this purpose, the OFMSW stabilization was well progressed in an anaerobic batch digester,namely a landfill bioreactor (LFBR), for measuring the specific methanogenic activities (SMAs) degradingcarbohydrate. protein, lipid. butyrate. propionate, and acetate. Furthermore, a model including the parameters ofmethane production lag-phase time, rate and potential was suggested to systematically describe the dynamics ofthe SMAs in the LFBR.

MATERIALS AND METIIODS

Composition of synthetic OFMSW

A synthetic organic fraction of municipal solid waste (OFMSW) wasused as the experimental material for this study. As listed in Table 1,the shredded OFMSW consisted of vegetables (27.0%), fruits (5.4%),meat (4.5%), rice (12.0%), paper (0.01 %) and dewatered sludge cake(51.1%). Except for the rice, each component was shredded to lessthan 2.0 em in particle size.

Experimental equipment and procedure

The OFMSW was incubated in ten 0.5-liter wide-mouth landfillbioreactors (LFBR. Figure 1). For each LFBR, 300 grams of theshredded OFMSW (Table 1) and 30 grams of seed sludge. obtainedfrom the municipal sewage treatment plant in Sendai City. Japan,were filled to capacity at the beginning of the experiment. Deionizedwater was added to the OFMSW for adjusting its moisture content to70% (wtJwt) to ensure the availability of ample free liquid for leachaterecycling. Leachate generation rates ranged from 60 to 120 ml.d',The LFBRs were operated with a weekly leachate recycle andmaintained at a constant temperature of 41 "C, the optimum temperaturefor mesophilic refuse decomposition (Hartz et al., 1982). The solidsin ten LFBRs was sequentially transferred into vials to measure eachindividual specific methanogenic activity degrading the carbohydrate,protein. lipid, and short-chain volatile fatty acids (VFAs) at an intervalof one-year.

Spednc methanogenic activity

Table 1. The composition of syntheticorganic fraction of municipal solid

waste used in this study.

Components Composition (%)

Vegetables 27.0

Fruits 5.4

Meat 4.5

Rice 12.0

Paper 0.01

Sludge cake 51.1

Figure 1. The schematic graph of thelandfill bioreactor used in this study.

The rates of methanogenesis by sample, usually incubated in a serum vial. can be readily measured and effect oforganic matter decomposition on these rates can be assessed. The potential of the methanogens in question todegrade an added methanogenic substrate or their precursors can be determined (Shelton and Tiedje, 1984).Thus. the specific methanogenic activity (SMA) test was performed with a 120 mL vial at 41 ·C. Glucose,peptone. linseed oil. acetate, propionate and butyrate were used as the individual substrate to determine the SMAof the sludge inside the LFBR. Among them, glucose, peptone and linseed oil were used as the typical substratesof the carbohydrates, proteins and lipids, respectively (Ogimoto and Imai, 1980). The composition of theincubation media is listed in Table 2 (Li and Noike, 1992) and a mixture gas containing 80% ~ and 20% CO2

was used as the headspace gas. The vials were then incubated in a rotary cell culture (Figure 2) rotated at 1.5rpm for providing better contact among samples. nutrients and microorganisms. The volume of biogas wasmeasured with glass syringes according to the approach reported by Owen et al, (1979). All these operationsproceeded under an atmosphere of 80% N2 and 20% CO2 using the Hungate technique (Miller and Wolin, 1974)

Dynamics of methanogenic activities in II LFBR 179

Table 2. Medium composition of SMA test

(a) Contains,In gramsperliter of distilledwater:nilJOlriaceticacid, 4.5;FeC1 a04Hp, 0.4; CoClz06HaO. 0.12;A1k(SO.~0.01;NaQ,l.O;ocr, 0.02;Na:MoO., 0.01;MnCla04HzO.0.10;H,BO,.0.01; CuSO..SH,O. 0.01 ; NiCla06H,0, 0.02.

(b) Contains,ln milligramsper liter of distilled water:biotin,2; folic acid, 2; pyridoxine HQ, 10; thiamineHCI, S;riboflavin, 5; nicotinicacid. S;DL~a1cium pantothenate.5; vitamin BI2, 0.1; p-amioobenzoic acid,oS; lipoicacid.0.5.

J

Figure2. A rotarycell culturedeviceused in this study.

01 _

Concentration

1.0 g.L-1

0.4 g.L"I0.4 g·L·11.0 g·L·110.0 mL10.0 mL4.0 g·L-10.21 g·L-10.5 g-L"0.25 g.L·l0.002 g·L·l7.0-7.2

Components

Organic substrateK~Po.KjlPO.NH.ClMineralsolution (a)

Vitamin solution (b)

NaIlCO,MgCI,~~O

CysteineHCl.HpN~S-9HP

ResazurinepH

to assurean anaerobiccondition.

The specific methane productionrate in each vial experimentusingeach individualsubstrate was defined as thespecific methanogenic activity degrading the corresponding substrate. In order to evaluate the SMA, themodified Gompertzequation shown by Eq. (I) (Layet al., 1996a; 1997a.b) was used to fit the experimental datain each vial experiment and the SMA was then obtained by dividing the methane production rate by the VSamountof the tested sludgesamples.

(I)

where M is the cumulative methane production (mL), t is the incubation time (day), A. is the lag-phase time(day),P is the methaneproduction potential (mL),R". is the methane production rate (mW·I ) , and e is exponential1 in a vial test

The dynamicsof specific methanogenic activity,Rift), for degrading each individual substrate in an LFBR wasdescribed using Eq. (2), which was the derivative of the cumulative methane production with respect to theincubation time (Lay et al., 1996b).

IW) =R,.,/ •exp{2 - exp[1+ R",~ . e(A.l - t)] + R".~. e(A.I -I)} (2)

Where PI is the methaneproductionpotential of componenti (mL), R....t is the maximummethane production rate

180 J. J. LAY et al.

of component i (mLogVSI-d.I ) , and Al is the lag-phase timeof component i (day).

Data analysis

The function of the 'solver' in MicrosoftExcel version 5.0, by converging the residual sum of square betweentheexperiment and the estimationto a minimum value,was usedto estimate the parameters of thesemodels. Allparameters were judged by the diagnosis procedure according to the approach reported by Wen et al. (1994)including the Student-t test. Dubin-Watson test (D), and Kalmogorov-Smirnov test (0.).

Analytical method

The percentage of methane and carbon dioxide in biogaswas analyzedusing a gas chromatograph (Shimadzu8A) equipped with a thermal conductivitydetector (TCD) and a 2-m stainless column packed with activatedcarbon (60/80 mesh). The operational temperatures of the injection port. the oven and the detector were 140.120and 140 ·C. respectively. Helium was usedas the carriergas at a flow rate of 30 mbmin". Calibration wasmade using 99.99% methane standard gas. The detection limit of the TCD was 0.1% for methane. Theconcentrations of the VFAsweredetermined by a secondgas chromatograph of the same model.equippedwithaframeionization detector (FlO) and a 2·m glasscolumnpackedwith KOCL·FM (60/80mesh). The operationaltemperatures for the injection port, the oven and the FlO were 160, 140 and 160 ·C, respectively. Before theanalysis of the VFAs, phosphoric acid was added to control the pH of the samples. The concentrations of totalsolids (fS) and volatile solids (VS) were determined by a lo-mL sample in the 105 ·C and 550 ·C ovens,respectively, according to the procedures described in the Standard Methods(APHAet al., 1992). The pH ofsamples weredetermined by a pH meter.

RESULTS ANDDISCUSSION

Measurement of SMA

To measurethe SMAsfor degrading differentsubstrates of the LFBR samplesat variousincubationtime,a totalof 42·SMAtest experiments werecarriedout on the substrates of lipid, protein, carbohydrate, acetate,propionateand butyrate. Subsequently, equation (1) was used to fit the experimental data of the cumulative methaneproduction curve in each individual vial test In this study, the specific methane production rate for a certainsubstrate was defined as the SMA of that substrate. As an example, a nonlinear fitting plot using Eq, (1) isshown in Figure 3. Table 3 summarizes the best values of the SMAs obtained by the data analyses. The

Table 3. Summary of the SMAdata degrading each individual substrate.

CarbohydrateProtein

SMA (roLCH•• gVS·I. d·l )

Butyrate LipidPropionateAcetate

Incubationtime -------------...;...------------

(days)

2570

120150200250300

2.4 (0.1)9.6 (0.8)

12.0 (0.5)

19.2 (0.8)33.6 (0.6)38.4 (0.5)24.0 (0.8)

4.8 (0.2)9.6 (0.5)

10.8 (0.4)

12.0 (0.3)14.4 (0.6)21.6 (0.7)16.8 (0.2)

7.2 (0.1) 1.2 (0.5)9.8 (0.4) 2.4 (0.6)

12.5 (0.2) 6.0 (0.7)15.1 (0.5) 7.2 (0.8)19.7 (0.6) 24.0 (0.9)

23.5 (0.9) 4.8 (0.5)28.8 (1.0) 2.4 (0.2)

2.4 (0.1)6.0 (0.2)7.2 (0.1)

19.2 (0.5)28.8 (0.9)16.8 (004)

4.8 (0.2)

24.0 (0.5)67.2 (0.4)48.0 (0.6)38.4 (0.8)14.4 (0.3)12.0 (0.5)7.2 (0.2)

Note: Data art tilt mtCUI 01twortplicattcultures.ValUtI ill partlltlltsu rtprtstllt sraruJard dtvialiolL

Dynamics of methanogenic activit ies in a LFBR 181

calculated values of 0 and D. for determining therandom normal distribution of the residuals ranged, respectively,froin 1.1 to 2.9 and 0.05 to 0.20, which were less than the table values of 3.05 and 0.36, indicating that ailresiduals had a random normal distribution of less than 5% random error. In addition, all of the t-values werelarger than that of t .m(l6) =2.14 (table value), where t =b1SE(b), whereas SE(b) and (b) represent, respectively,the standard error of b and all parameters to be estimated. This indicates that the parameters were taken to bestatistically significant at a confidence interval of 95% (Box et al., 1978).

Dynamics of specific methanogenic activities in the LFBR

Figure 4 shows the dynamics of SMAs degrading different substrates in the LFBR, illustrating that the SMAsrose to a peak: and gradually declined. Equation (2) was used to quantitatively describe the dynamics curves ofSMA in the LFBR. The best values of the parameters, PI' RmJ and A.I, for fitting the experimental data weredetermined using the same analysis procedure as used for Eq. (1). Here, the~ represented the maximum

e

8

",

III

120

12~ tCarbohydrate -'l~-e--E~--80 ~Q g e

40i~

12~~ J!:~BB B

i~··· t

i[~~,·1~ 6

fE Propionate II ia :: ll:':::EGll-~_....I_,,_,-_,,_-_-_,j;_-_._....... ..... J

~"":-eta-t-e-"-,,,-,~[Il-..-...-•••-.I-:-m-iil-iil----ro 40 80

Incubation time [hours)

Figure 3. The detennination of SMA for degrading various typical substrate. The R". is themethane production rate in Eq. (1).

182 J. J. LAY et al.

specificmethanogenic activity. SMA",. In Figure4. the marksand the solid lines representedexperimentaldataand the fitted model predictions by Eq. (2). indicatingthat Eq. (2) was suitable for describing the dynamicsofmethanogenic activity on a certain substrate.such as protein. lipid.carbohydrate and each individualVFA. Theevaluatedvaluesof these key parameterswere summarized in Table 4. In Table 4. the~ of lipid. 160 days, waslargerthan that of protein. 145days. while both of them weresignificantly larger than those of carbohydrateandVFAs. Similar results were obtained for a batch high-solids sludge digestion. The lag-phase time of methaneproduction might reflect a period of hydrolysis/fermentation. which corresponds to the rate ofhydrolysis/fermentation of an anaerobicmicrobial process(Layet al.• 1997b). During this period. the pH valuein the leachateof the LFBR was around6.0 or below. The pH of the system is importantfor the optimalgrowthof proteinsllipids-degrading bacteria. For example. in the continuous culture study of entile ruminal contents.the proteins-degrading bacteria are washed out of the system as the pH dropped to 5.5 (Diirre and Andreesen,1982). This result was due to the fact that the mediation of exo-enzymes was excreted by fermentative bacteria.The protein is degraded to amino acids. the carbohydrate is transformed into soluble sugars and the lipid isconverted to long chain fatty acids and glycerine (Gujer and Zehnder. 1983). Moreover. the results were inagreement with thosepreviouslyobtainedfrom a mesophilic batchdigesterfed with rice and potato. in whichthemain componentis carbohydrates. at differentmoisture contents (Layet al.• 1996a).the growth of methanogensin the low moisturecontent of solid-beds were inhibited by the low pH or high level of VFA. In Figure 4. theSMAapproachesto the SMA· at a critical incubation time.)..·. Each)..· for the substrateof acetate. propionate.butyrate. carbohydrate. protein and lipid was 95. 100.94.92. 190 and 200 days. Apparently. the )... of theproteinand the lipid were larger than those of acetate.propionate. butyrate, and the carbohydrate. Considering

Protein Propionate

Upld Acetal.

100 200 300 0 100 200 300nme [day.]

Figure4. Dynamicsof SMAdegrading each individual substratein the LFBR.

Table 4. Summaryof Key Parameters for Describing Dynamics Curves using Eq. (2).

Acetate Propionate Butyrate Carbohydrate Protein Lipid

RIIol (mLCH.- gVS·I. d·l ) 36.0 15.6 28.8 39.0 28.0 20.0

A.. (days) 33.0 30.0 36.0 25.0 145.0 160.0x (days) 95.0 100.0 94.0 92.0 190.0 200.0

Dynamics of methanogenic activities in a LFBR 183

these results together with the X. the decomposition of proteins and lipids might overrule the LFBR treating theOFMSW. Additionally. as listed in Table 4. the SMA", of acetate was higher than those of propionate andbutyrate. In general. the products of acetogenesis, such as propionateand butyrate. are converted into the fmalproducts for methane production: acetate. hydrogen and carbon dioxide. There is a symbiotic relationshipbetweenacetogens and methanogensdue to the fact that the activity of acetogens depend on the substrate inputand the activity of the methanogens(Shink, 1989). As a result, the examination of the methanogenicactivitiesofacetate. propionate and butyrate suggested that the rate of methanogenesis was higher than that of acetogenesisduringthe anaerobicmineralizationof the OFMSW.

Methane production rate In the LFBR

TheLFBRstabilization is a dynamics and microbially-mediated process. Because proteins. lipidsandcarbohydratesare the main fermentativecomponentsof the OFMSW. the overall methaneproduction rate in the LFBR can bedefined as the summation of methane production rates on each component including the protein. lipid andcarbohydrate. In order to elucidate the relationship between the decomposition of the OFMSW and the methaneproduction rate in the LFBR. the methane production rate estimated using Eq. (2) was compared with that ofobservation (Figure S). An examination of Figure S reveals that the correlation coefficient, r2. between themethane production rate of the observation and that of estimation was larger than 0.90. illustrating that theformer approximatelycoincided with the latter. By comparingFigures4 and S reveals that the first peak of themethaneproduction rate in Figure S was mainlycausedby the degradation of the carbohydrate. while the secondpeak was mostly caused by those of the protein and the lipid. It has been reported that the LFBR stabilizationneeds to proceed through the methane fermentation phase and into the final maturation phase (Pohland, 1996).Obviously. in this study. the stabilization of the OFMSW in an LFBR was significantly influenced by theconversionof the protein and the lipid into methane. Thus. the period of X· (refers to Figure 4) of the proteinand the lipid of the sludge containedin the LFBRsignificantly overruled the efficiency of the LFBR treating theOFMSW.

60 100 150 200 250 350

Time [day.]

Figure S. Observedand estimated methane production rates in the LFBR.

CONCLUSIONS

Basedon the results and discussion.the principle conclusions derivedfrom this investigationare as follows:

(1) The simple model used in this study was suitable to describe the dynamicsof methanogenic activity for theLFBR treating the OFMSW. By using this model. the key parameters. maximum methane production rateand lag-phase time. for the OFMSWdecomposition can be exactlyestimated.

(2) According to the dynamics of methanogenic activities and each individual substrate degradation conductedin this study. the decomposition of proteins and lipids might overrule the stabilization of the LFBR treatingthe OFMSW;while the rate of methanogenesis was higherthan that of acetogenesis.

184 J. J. LAYeral.

(3) Experimental and estimated data, confirmed by the dynamics of methanogenic activity, suggestedthat theperiod of ).+ of the protein and the lipid of the sludge contained in the LFBR significantly influenced theefficiency of the LFBRtreating the OFMSW.

ACKNOWLEDGMENTS

The authorswish to thank Mr. S. Agatsuma for his excellent technical assistance. Duringthe time muchof thiswork wasperformed, Y.Y.U wasan associate professor in theDept. ofCivilEngineering, Faculty of Engineering,Tohoku University. We wouldalso like to thankProf. S. Ghosh for hisdiscussions on the research proposal.

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