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International Biodeterioration & Biodegradation 83 (2013) 41e47

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International Biodeterioration & Biodegradation

journal homepage: www.elsevier .com/locate/ ibiod

Anaerobic mesophilic digestion of waste activated sludge in thepresence of 2,30,4,40,5-pentachlorobiphenyl

Devrim Kaya a,b, Ipek Imamoglu a, F. Dilek Sanin a,*

aDepartment of Environmental Engineering, Middle East Technical University, 06800 Ankara, TurkeybDepartment of Environmental Engineering, Kocaeli University, 41380 Kocaeli, Turkey

a r t i c l e i n f o

Article history:Received 28 February 2013Received in revised form5 April 2013Accepted 8 April 2013Available online 4 May 2013

Keywords:Anaerobic digestionDechlorination2,30 ,4,40 ,5-PentachlorobiphenylTransformer oilWaste activated sludge

* Corresponding author. Tel.: þ90 312 210 2642; faE-mail addresses: devkaya@gmail.com (D.

(I. Imamoglu), dsanin@metu.edu.tr (F.D. Sanin).

0964-8305/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.ibiod.2013.04.003

a b s t r a c t

The aim of this study was to investigate the anaerobic digestion of waste activated sludge in the presenceof a model PCB congener, 2,30 ,4,40,5-pentachlorobiphenyl (PCB-118), and transformer oil (TO), andthereby PCB dechlorination under mesophilic digestion conditions. Two PCB-118 concentrations (1 and20 mg/L) and one TO concentration (1.52 g/L) were studied. Beside the PCB concentrations, pH, ORP, TS,VS, VSS, TSS, tCOD, and sCOD were monitored throughout the reactor operations (159-day). Methaneproductions of PCB reactors were considerably lower than that of control reactor (R-C), indicating thenegative effect of PCB on methane production. The highest COD removal, 56%, was observed in R-C,followed by 1 and 20 mg/L PCB-118 reactors (46.7% and 40.6% reduction), respectively. VS reductionswere between 36 and 52%, with the lower removal in the higher PCB-118 containing reactor. About 12and 22% PCB-118 removals were attained proportional to their initial concentrations, 1 and 20 mg/L,respectively.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Large quantities of sludge are produced in the treatment ofmunicipal and industrial wastewaters. Waste activated sludge(WAS) being a by-product of a biological process consists of com-plex organics, mainly protein (approximately 30%), carbohydrate(approximately 40%) and lipids (approximately 30%) in particulateforms (Appels et al., 2008). WAS must be stabilized sufficiently toreduce its organic content so that it can be safely disposed ofwithout causing odor problems and/or spread of pathogens. Sludgestabilization through anaerobic digestion is a commonly appliedprocess because of its ability to transform organic wastes intobiogas (60e70 vol% of methane, CH4), bringing the potential ofusing the biogas as an energy source (Appels et al., 2008). TheEuropean Union has put an objective to increase the amount ofenergy obtained from renewable sources from the 2005 level of8.5e to 20% in 2020 (Mottet et al., 2010). In this context, anaerobicdigestion of WAS may contribute to reach this objective.

Several aliphatic, aromatic and halogenated hydrocarbons,heavymetals, detergents and long-chain fatty acids widely found inmunicipal wastewaters are either non-biodegradable or slowly

x: þ90 312 210 26 46.Kaya), ipeki@metu.edu.tr

All rights reserved.

biodegradable. Since most of these chemicals are highly hydro-phobic they accumulate on sludge to various extents (Ruiz and Soto,2009). PCBs are among these chemicals. They are non-biodegradable; persistent in the environment; able to accumulatein fatty tissues in the body; and suspected of being carcinogenic(USEPA, 1988). Although both the production for industrial use andthe discharge of PCBs have been banned in many countries sincelate 1970s, contamination of the environment with PCBs still occursand is of great public concern which has led the European Unionand many other countries to regulate the PCB concentrations in airand water as well as sludge. Although PCBs were never produced inmany countries such as Turkey, transformers containing oil withPCBs are currently known to be used in the production/trans-mission of electricity (UNIDO, 2002). Therefore, following ratifica-tion of the Stockholm Convention on January 2010, the TurkishMinistry of Environment and Urbanization is held responsible forthe preparation and implementation of waste management plansregarding the elimination of equipments containing PCBs via theNational Regulation for the Control of Equipments Containing PCBand PCTs. Disposal of these and especially oil containing PCBsconstitutes a major problem. The biological degradation of PCBsunder anaerobic conditions has been observed in a variety ofcontaminated matrices, such as sediments (Berkaw et al., 1996;Fagervold et al., 2011; Payne et al., 2011) and anaerobically digestedactivated sludge (Ye et al., 1992; Phelps et al., 1996; Chang et al.,2002; Fava et al., 2003). However, work in the presence of

D. Kaya et al. / International Biodeterioration & Biodegradation 83 (2013) 41e4742

transformer oil (TO) is limited. Hence, an elimination strategy ofPCB with TO in anaerobic digesters may prove to be useful.Although the performance of anaerobic digesters is expected to benegatively affected by the presence of these trace contaminants, afull investigation of digester performance in the presence of PCB-118 and TO was not investigated before.

PCB concentrations in naturally contaminated sludge aregenerally reported between 1 and 10 ppm (Patureau and Trably,2006; Benabdallah El-Hadj et al., 2007; Bertin et al., 2007). There-fore, during this study, 2,30,4,40,5-pentachlorobiphenyl (PCB-118)was selected as a model PCB congener due to its toxicity and highabundance in Aroclor 1254, main constituents of TO, and itswidespread detection in the wastewater sludges. The performanceof anaerobic mesophilic digesters treating WAS in the presence ofPCB-118 and transformer oil was investigated and for this purpose,1 mg/L was chosen as low-level, while 20 mg/L was chosen as thehigh-level dose of PCB-118 in this study. The main indicators wereselected as the methane production, solids and COD reduction, aswell as PCB dechlorination.

2. Material and methods

2.1. Chemicals

Sulfuric acid (98%), sodium sulfate (granular), fine copperpowder (Cat. no: 1.02703.250), n-hexane and acetone were pur-chased from Merck KGaA (Darmstadt, Germany). All individualstandards of pure PCB congeners (nos.118, 70, 67, 66, 33, 25, and26), surrogate standard, TMX (2456-Tetrachloro-m-xylene solu-tion), internal standard (IS), PCB-209, and PCB-Mix-3 (nos.28, 52,101, 118, 138, 153, and 180) were purchased from Dr. EhrenstorferGmbH. The purity of all PCBs were 99% or higher. PCB-free trans-former oil (TO) was purchased from SigmaeAldrich Co., USA. Acertified reference sewage sludge (Cat. no: LGC6184), containingseven indicator PCBs (PCB-Mix-3 congeners) was purchased fromLGC standards, Germany and used for quality assurance of extrac-tion and analyses. Alconox detergent (White Plains, NY, USA) wasused for cleaning of all glassware.

2.2. Experimental setup

Mixed culture anaerobic digester sludge (ADS) used as seed wastaken from one of the anaerobic digesters of Ankara CentralMunicipal Wastewater Treatment Plant in Turkey. Digesters wereoperated in mesophilic range at 35 �C with a sludge retention time(SRT) value of 24 days. Waste activated sludge was taken from thereturn line of secondary sedimentation tanks from the same plant.The conventional activated sludge plant has been in operation since1997 with a current average wastewater flow rate of 746,000 m3/day. ADS was filtered through a screenwith a mesh size of 1 mm toeliminate coarse suspended particles present. Both WAS and ADSwere settled for 12 h to increase the solids concentration bydecanting overheadwater and stored at 4 �C prior to use. Initial F/Mratio (gVS/gVSS) was set to about 1. Sludge samples were analyzedfor their TS, VS, TSS, and VSS concentrations before adding theminto the reactors and the results are given in Table 1.

Anaerobic batch reactor system consisted of 8 reactor sets, eachconsisting of a 3.2 L anaerobic reactor with a 4-L graduated cylinder

Table 1TS, VS, TSS, and VSS values of WAS and ADS at reactor set-up.

Sludge TS (mg/L) VS (mg/L) TSS (mg/L) VSS (mg/L)

WAS 11460 � 85 8647 � 19 11197 � 231 8550 � 14ADS 27017 � 259 12333 � 94 26460 � 453 12130 � 325

gas collector which was connected to the anaerobic reactor fromthe top by PTFE pipes. Before filling up the reactors, all the con-nections and parts were examined for leak-proof condition. Gascollectors were graduated in 10 mL intervals and filled with brinesolution (10% NaCl, w/v and 2% H2SO4, v/v) in order to prevent CO2solubility (Parajuli, 2011). As the gas was produced, the solutionlevel was pushed down and the measured volume was recorded.

Reactors designated as R-1 and R-20 were biotic reactors spikedwith PCB-118 at doses of 1 mg/L and 20 mg/L, respectively. R-Awasoperated as abiotic control reactor which was autoclaved at 121�Cfor 1 h prior to PCB-118 spike at a final concentration of 1 mg/L.PCB-free TO was also included as one of the reactor constituentsand added to the reactors at 1.52 g/L. The density of TO was889.2 � 17.0 g/L and its VS and TS values were almost equal to eachother (876.7� 27.2 g/L). Moreover, another pair of reactors, R-C thatreceived neither TO nor PCB-118 was operated as biotic control. Inthis study a control reactor with transformer oil was not operated.Previously, the toxicity of PCB-118 was evaluated by an AnaerobicToxicity Assay (ATA) (Kaya, 2012), and TO effect on CH4 productionwas found to be insignificant in the range of 0.38e1.52 g/L.

Reactors were filled with 1200 mL of WAS and 1400 mL of ADS.Any micro/macro nutrients or pH regulating chemicals were notadded to the reactors assuming that sludge contains enough nu-trients and buffer. Thus, 2.6 L of 3.2 L reactor volumewas filled withWAS, ADS, and TO; hence, 0.6 L was left empty as headspace. Afterfilling all the reactors, each reactor was purged with N2 gas for10 min to remove oxygen from the system. Then, the reactors weresealed with natural rubber stoppers and incubated at 35 � 1 �C inthe dark. Continuous mixing was supplied by magnetic stirrers at250 rpm throughout 159 days of reactor operation. PCB-118 stocksolutions were prepared in acetone, and spiked to the reactors(0.38%, v/v: acetone volume/effective reactor volume) to supply thetarget concentrations. About 2 h after PCB-118 spike, all reactorswere sampled to reveal the initial conditions and also to checkwhether the desired PCB-118 concentrationwas reached. A numberof parameters including total gas volume and gas compositionwereanalysed initially and then at predetermined time intervals. TotalCOD (tCOD), soluble COD (sCOD), TS, VS, TSS, VSS, pH, oxidation-reduction potential (ORP), and PCBs were also analyzed initiallyand then at following days: 11, 23, 29, 35, 41, 47, 54, 61, 74 and 159 d.

PCB-118 and its possible daughter products (PCB-25, 26, 33, 66,67, and 70) were analyzed in each sample. PCBs were analyzed bothin slurry samples (containing solids and liquid portion of reactorcontent) and the filtrate of slurry samples (liquid portion).

The primary objective was to investigate the effect of PCBs onanaerobic digesters in the presence of TO, therefore, PCBs and TOwere added together to the reactors. While PCB removal was ofconcern, TO degradation was not within the scope of the study andhence was not monitored. Duplicate reactors were operated for 159days. Two samples were taken from each reactor at the pre-determined sampling times. Therefore, the results presented hereare the averages of these four measurements.

2.3. PCB extraction procedure

For PCB extraction, a 2-mL slurry sample was taken into a 22-mLglass vial sealed with a PTFE screw cap. After the addition of 50 mgreduced copper (pre-washed with hexane and acetone; dried withN2) and surrogate (TMX), PCBs in the sample were extracted byvigorous overnight-shaking on a horizontal platform shaker at350 rpm with 10 mL of n-hexane. Afterward, sample and hexanewere separated by centrifugation at 2500 rpm for 5 min. Afterpassing the extract through a glass column packed with anhydroussodium sulfate (Na2SO4), it was concentrated down to 2 mL byapplying nitrogen blowdown technique (USEPA, 1996) and 1-mL of

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Fig. 1. Cumulative methane productions of reactors with respect to incubation time.

D. Kaya et al. / International Biodeterioration & Biodegradation 83 (2013) 41e47 43

this eluate was taken into a 2-mL borosilicate glass GC vial and ISwas added before GC analysis. The same PCB extraction procedurewas applied to the filtrate of sludge samples taken from the reactorsand filtered through 0.45 mm pore sized filters. Due to a smallvolume loss during the extraction, final results were volume cor-rected. Other details were given by Kaya (2012).

2.4. Analytical methods

PCB analysis was done following IS calibration procedure ac-cording to USEPA Method 8082 (USEPA, 2000) by using a GC/ECD(Agilent/6890N) equipped with a HP-5MS capillary column(30m � 0.25mm � 0.25 mm). A 5-point calibration curve was usedfor each congener with RSDs <20% and r2 > 0.99. GC experimentalconditions for PCB analyses were as follows: Helium was used asthe carrier gas (1.5 mL/min) and nitrogen was used as the make-upgas (20 mL/min). The injection mode/temperature was splitless/250 �C; the detector temperature was 350 �C. The initial oventemperature was set to 100 �C and then increased to 160 �C with aramp of 20 �C/min, and it was held at 160 �C for 2 min. Then, it wasincreased to 200 �C with a ramp of 3 �C/min and from 200 to 240 �Cwith a ramp of 8 �C/min and it was held at 240 �C for 5 min. Then, itwas increased to 290 �C with a ramp of 30 �C/min and held at290 �C for 3 min.

Total gas production was directly read from the gas collectors.Gas composition (CH4, CO2) was analyzed according to StandardMethods Section 2720C (APHA, 2005) with GC/TCD (Agilent/6890N) equipped with HP-PlotQ capillary column (30.0m �530mm � 40.0 mm). GC experimental conditions for gas analyseswere as follows: Helium was as the carrier gas (3 mL/min). Theinitial temperature of the oven was set to 45 �C and held for 1 min;then temperature was increased to 65 �C with a ramp of 10 �C/min.A four-point linear calibration curvewas used for the quantificationof CH4 and CO2 gases with r2 > 0.99.

COD analyses were conducted according to a USEPA approvedmethod (Hach, 1998). Prior to sCOD analysis, samples were filteredthrough 0.45 mm pore sized filters (Millipore). Solid analyses (TS,VS, TSS and VSS) were done according to Standards Methods Sec-tions 2540B-D-E (APHA, 2005). pH and ORP values were measuredwith a pH/ORP meter (EC-PH510/21S, Eutech Inst.).

2.5. Statistical evaluation

The Student’s t-test was used to assess the statistical signifi-cance of the data. The level of significance was set at value of(p) < 0.05. All statistical evaluations were performed by GraphPadPrism 5.04 software.

2.6. Quality assurance/quality control (QA/QC)

The accuracy and precision of PCB measurements werecontrolled by calculating the surrogate recoveries as well as re-coveries from the certified reference sludge, which were between82e108% and 82e103%, respectively. Recoveries were within theacceptable range of USEPAMethod 8082 (80e120%). In addition, foreach batch of 10 sludge samples, a method blank, and a laboratorycontrol sample were analyzed, with satisfactory results. Methoddetection limits (MDL) (n¼ 7) for PCB-118 and TMXwere 57 ppt and32 ppt, respectively. Limit of quantitation (LOQ) (n¼ 7)were 180 pptand100ppt for PCB-118andTMX, respectively.MDLs and LOQswerecalculated according toMuir and Sverko (2006). All target PCBswerelower than the LOQ inmethod blanks. Therefore, surrogate recoverycorrection or blank subtraction was not performed. USEPA MethodSW-846 Chapter 4 was followed for all glassware cleaning (USEPA,2007). Coefficient of variance was typically lower than 10% for all

digester performance parameters, showing that the quality ofmeasurements was good and acceptable.

3. Results and discussion

3.1. Anaerobic digester performance

Fig. 1 shows cumulative methane productions of all reactorswith respect to incubation time. Initially, in all of the reactorsrelatively high biogas production rates were observed. As biodeg-radation proceeded with time, depletion of available substratesresulted in a gradual decrease in biogas production in all reactors.As seen from Fig. 1, the cumulative CH4 production showedconsistent decrease with the increase in PCB-118 dose. As soon asthe fifth day of operation was reached, the methane productions ofPCB reactors fell behind the control reactor. The highest methaneproduction was observed in PCB-free control reactor (R-C) with thetotal production of 10,427.4 � 55.4 mL in 159 days. This was fol-lowed by that of R-1 and R-20 as 8159.2 � 45.0 mL and5706 � 33.2 mL, respectively. The decrease in methane productionof R-1 was 22% and R-20 was 45% compared to that of controlreactor. Also, as the PCB concentration increased from 1 mg/L to20 mg/L, the methane production at 159 days decreased by about30%, as a clear indication of the negative effect of PCB-118 presenceand dose. It was clear that the higher the PCB dose was, the lowerthe methane production obtained in the reactors.

As mentioned above, it was found that the TO presence at dosesof 0.38e1.52 g/L had an insignificant effect on CH4 production(Kaya, 2012). Although the methane percentage of the reactors inthis previous study was affected slightly by the presence of TO, thevalues ranged between 54 and 63%, which were all acceptablebased on the typical performance of anaerobic digesters (De LaRubia et al., 2002). Therefore with this observation, it waspossible to say that the decrease in gas production was related tothe PCB-118 rather than the transformer oil.

The variations of TS and VS, which are important digester per-formance parameters, with operation time are plotted for eachreactor in Fig. 2a and b, respectively. As seen from these figures, TSand VS reduction in PCB containing reactors were lower than thatobserved in the control reactor. The reductions observed in R-C, R-1,and R-20 were about 40%, 31%, and 24% for TS, and 57%, 45%, and35%, for VS, respectively (Table 2). The reason for lower reductionsobserved in the presence of PCB was taken as the negative effect ofPCB-118 on the digester performance.

The TSS and VSS variations for each reactor are given in Fig. 2cand d. Similar trends observed in TS and VS removals were also

Fig. 2. Variation of a) TS, b) VS, c) TSS, d) VSS, e) tCOD, f) sCOD, and g) pH values of the anaerobic reactors throughout 159 days of incubation.

D. Kaya et al. / International Biodeterioration & Biodegradation 83 (2013) 41e4744

observed in TSS and VSS removals of the reactors. TSS and VSS re-movals were in the range of 43e25% and 56e38% (Table 2),respectively,with the highest removals observed in PCB-free reactor(R-C) and then decreasing with the increase in PCB-118 dose.

The results for tCOD for each reactor are plotted in Fig. 2e. Therewas considerable tCOD reduction in all biotic reactors, with the

Table 2Comparison of the reactors in terms of treatment performances at day 159.

Reactor VS removal, % TS removal, % VSS removal, % TSS

R-1 45 � 1.2 31 � 1.4 46.6 � 0.7 33.R-A 2.6 � 0.1 3.1 � 0.8 3.9 � 0 3.R-20 35.4 � 0.6 23.6 � 0.7 37.9 � 0.5 24.R-C 57 � 1.1 40.4 � 0.6 56.4 � 0.3 43.

highest tCOD removal achieved in R-C (biotic control) at about 57%.This was followed in a decreasing order by 1 mg/L and then by20 mg/L PCB-118 reactors with about 47% and 39% reductions,respectively (Table 2). tCOD reduction of abiotic reactor wasinsignificant, so it indicated that R-A was well sterilized and wouldrepresent the abiotic losses. The tCOD reduction results obtained in

removal, % tCOD removal, % mL CH4/gVSadded Final pH

3 � 0.4 47.2 � 0.7 347.2 7.16 � 0.075 � 0.2 2.7 � 1 0.9 7.12 � 0.05 � 1.1 39.1 � 0.3 242.5 7.29 � 0.014 � 0.5 57.3 � 0.5 443.1 7.28 � 0.04

D. Kaya et al. / International Biodeterioration & Biodegradation 83 (2013) 41e47 45

biotic reactors are in the range of typical digester performancevalues reported in the literature for COD between 40 and 60% undermesophilic conditions (Appels et al., 2008).

Fig. 2f presents sCOD values of all reactors measured during 159days of the reactor operations. There were fluctuations in sCODvalues of the reactors throughout the operation time as expectedbecause organic compounds are hydrolyzed/solubilized and thenconverted to methane during anaerobic digestion. The high tem-perature during autoclaving resulted in an increase in the solublewaste (solubilization of COD) explaining the relatively high initialsCOD of R-A (Fig. 2f). sCOD continued to increase in this reactor,indicating that hydrolysis was active, but not methanogenesis sincenegligible amounts of sCOD consumption and methane production(Fig. 1) were observed. The observed pH decrease during theoperation of R-A (Fig. 2g) also confirms this hypothesis.

The pH value of other reactors behaved as expected during thereactor operation and remained within the optimal operation pHfor methanogenesis (6.8e8) (Speece, 1996) and also mostly in therange for optimum PCB-dechlorination (7.0e7.5) (Borja et al.,2005). Furthermore, all the ORP values determined werebetween �214 and �330 mV, indicating a proper anaerobic envi-ronment (Gerardi, 2003).

The methane yields expressed in terms of cumulative methaneformed per gram of VS added into the reactors are given in Table 2.It is seen that the yield decreasedwith the increase in PCB-118 dose.The specific gas production of R-C, 443.1 mL/gVSadded, was consis-tent with the literature data reported as 370e506 mL/gVSadded(Benefield and Randall, 1980) showing proper anaerobic digestionof WAS under mesophilic conditions. Although it can be concluded

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that the PCB containing reactors were negatively affected, lowerconcentration PCB reactors (R-1) could still maintain specific gasproduction values close to the cited literature data.

3.2. PCB-118 removal

The results of PCB-118 measured in slurry samples of the re-actors throughout the operation time are presented in Fig. 3. PCBconcentrations showed a decreasing trend with reactor operationtime; more so for 20 mg/L reactor when compared to 1 mg/Lreactor. The highest PCB-118 removal was attained in R-20 reactorat about 22% (Fig. 3b), while it was 12% in R-1 reactor (Fig. 3a). Theobservation of a greater reduction in 20 mg/L reactors may indicatethe presence of anaerobic dechlorination in these reactors. Thisresult is consistent with discussions regarding low PCB concen-tration being a limiting factor during anaerobic dechlorination(Borja et al., 2005). Also, it was reported that in the range of 1e10 ppm, higher dechlorination rates were observed for the higherPCB concentrations studied (Chang et al., 1999).

Although not major, there was 5% PCB-118 loss in the abioticreactor, R-A (Fig. 3c). When PCB-118 results of biotic and abioticreactors throughout the 159 days of incubation are statisticallyevaluated, it was found that PCB-118 removal in the biotic reactorswere significantly different (p < 0.05) from the abiotic ones.Accordingly, PCB-118 removal in R-1 and R-20 by biologicalmechanisms was significant.

Possible daughter products (PCB-25, 26, 33, 66, 67, and 70) ofPCB-118 dechlorinationwere also checked in both slurry and filtrateof slurry samples. There was a fluctuating increase in PCB-66

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(230440-tetrachlorobiphenyl) and PCB-70 (230405-tetrachloro-biphenyls) as well as in PCB-26 (2305-trichlorobiphenyl) concen-trations (data not shown) inmostly R-20 reactorwhich received thehigher dose of PCB-118. PCB-66 production results from meta-chlorine removal from PCB-118, while the presence of PCB-26 in-dicates the sequentialpara-chlorine removal fromPCB-118 andPCB-70. However, the levels of these congeners were typically less than10 ppb and were much smaller when compared to the reduction inthe mother congener, PCB-118.

The amount of PCB-118 in the filtered samples was generallybelow 50 ppb (data not shown). None of the possible daughterproducts were observed in the filtered samples. It is probable thatall the PCBs were adsorbed to the solids when considering thehydrophobicity of these chemicals. Similar results were alsoobserved by Patureau and Trably (2006). No dechlorination by-products for none of the PCBs (52, 101, 118, 138, 153 and 180)were reported in that study despite the abiotic loss at about 20%and biotic PCB reduction between 40 and 100% in anaerobic and/oraerobic reactors. The reason of the higher PCB removal efficienciesin that study was possibly due to the higher TS content of thesludge (32,000 mg/L) (Patureau and Trably, 2006). The VS contentof that cited study (26,000 mg/L) was about 3 and TS content wasabout 1.5 times higher than those of our study. Indeed, it waspreviously shown that higher solid concentration caused higherrate of adsorption in sludge when the dechlorination rates ofsamples with TS of 10 g/L and 5 g/L were compared (Chang et al.,1999). No abiotic losses were recorded in the same study, but theexperiment was conducted under batch conditions without mixing(Chang et al., 1999). Also, it was reported that PCB degradationoccurred only in the reactors containing acclimated consortia andwhen 1 ppm PCBs was added initially, the accumulation of only oneof the daughter products at about 0.4e0.5 ppm was observed(Chang et al., 1999).

There might be a number of reasons for not observing any orobserving very low concentration of daughter products such as thecase of this study. One of these reasons could be the absence ofadapted consortium in the reactors. Another reason might be theabiotic loss of PCBs through volatilization or other mechanisms. It isknown that abiotic loss of PCBs occurs as a result of volatilization,photo-degradation or chemical combination with organic matterbecause of the semi-volatile and hydrophobic nature of PCBs (Wu,1996; Patureau and Trably, 2006). Photo-degradation is not aconcern here, since experiments were conducted in the dark.However, loss by volatilization may be a more likely mechanismbecause PCBs, especially those that have undergone significantmicrobial dechlorination, are very susceptible to volatilization(Beyer and Biziuk, 2009). Even though volatilization of PCB-118 islimited due to its physicochemical properties, the behavior ofdaughter products can be significantly different. Since they arelower chlorinated and lower molecular weight compounds, acertain fraction of them may indeed partition into the gas phase.PCB-118 and its daughter products were not monitored in the gasphase and this route might explain some of the daughter productsthat are not accounted for. Overall, it can be judged that about 5%PCB-118 removal was due to abiotic losses, while the remainderwas due to biological means.

4. Conclusion

All results of digester parameters were consistent and showedsimilar trends as the methane formation: consistently lower re-movals in the order of biotic control, 1 ppm, 20 ppm and abioticcontrol reactors. The presence of PCB-118 and increase in its doseaffected digester performances negatively to a certain extent butfavored PCB-118 removal. Overall, despite the negative effect of

PCB-118 concentration on anaerobic WAS digestion, evidence ofsatisfactory methane production and acceptable removal rates forTS, VS, COD, and PCB-118, suggested the possibility of WAS degra-dation in the presence of low concentration of PCB-118 and TO.

Acknowledgements

This research was funded by OYP program of The Turkish Min-istry of Development (Grant#: BAP-08-11-DPT-2002K121010 DPT)and by Middle East Technical University Scientific Research Fund(Grant#: 7010311).

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