Toxicity Reduction of Municipal Wastewater by Anaerobic-anoxic-oxic Process

BIOMEDICAL AND ENVIRONMENTAL SCIENCES 23, 481-486 (2010)www.besjoural.comToxicity Reduction of Municipal Wastewater byAnaerobic-anoxic-oxic Process'MAN-HONG HUANGt, YONG-MEI LI*,AND Guo-WeIGU*"State Key Laboratory of Pollution Control and Resources Reuse, College of EnvironmentalScience and Engineering, Tongji Universiy, Shanghai 200092, China;* College of Environmental Science and Engineering,Donghua University, Shanghai 201620, ChinaObjeetive This study was conducted to optimize the operational parameters of anaerobic anoxic-oxic (A7/O) processesto reduce the toxicity of municipal wastewater and evaluate its ability to reduce toxicity. Methods A lumincscent bacteriumtoxicity bioassay was employed to assess the toxicity of infuent and efluent of each reactor in the A/0 system. ResultsThe optimum operational parameters for toxicity reduction were as fllows: anacrobic hydraulic retention time (HRT)-2.8 h,anoxic HRT = 2.8 h, aerobic HRT = 6.9 h, sludge retention time (SRT) = 1S days and intemnal recyele ratio (IRR) = 100% Animportant toxicity reduction (%) was observed in the optimized A7/O process, even when the toluene concentration of theinfluent was 120.7 mg:L" . Conclusions The toxicity of municipal wastewater was reduced significantly during the A/Oprocess. A/0 process can be used for toxicity reduction of municipal wastewater under toxi-shock loading.Key words: A/O process; Municipal wastewater, Toxicity reduction; Process opimizaion; Toxic-shock loadingINTRODUCTIONachievedl+dl. However, few studies have focused onthe ability of the A/O process to reduce the toxicityAssessment and optimization of wastewaterof municipal wastewater.treatment processes are often based on the polutantIt is well known that municipal wastewaterremoval efficiency. Wastewater treatment wascontains many types of toxicants with the potential tooriginally developed with the primary goal of ham humans'However, analyses forreducing odor in receiving waters; therefore, BODsconventional indices, such as COD and singleand SS were the primary evaluation indices. Later, intoxicant analysis, cannot enable a complete responsethe 1970s, nitrogen and phosphorus removal wereto the potential adverse effects of wastewater onrequired to protect the reeiving waters fromwildlife and humans due to the different interactionseutrophication. As a result, many existing wastewaterand biological activities found in municipaltreatment facilities were upgraded to accomplish thiswastewater' 4. With the development of wastewatergoal. Among the available advanced biologicalreuse, there has been increased community concemwastewater treatment processes, A/O was often usedover the ecotoxicicology and environmental safety offor simultaneous nitrogen and phosphorus removal.wastewater. Thus, there has been great demand forIndeed, this method has been applied widely duringevaluation of the ability of curently availablethe last three decades in municipal wastewaterwastewater treatment processes to reduce toxicity.treatment plants (MWWTPs). Witb the developmentAccordingly, the present study was conducted toof reactor kinetics and a better knowledge ofoptimize the operational parameters of the A/Omicrobiology ecosystems, many advances in theprocess and evaluate its toxicity reduction ability. Theremoval of conventional items by A7/0 have beenA/O process was conducted at the laboratory-scale'This study was supported by the National Science Foundation Project grants of China (No. 50878165, No.21007010), the Program forNew Century Excellent Talents in University (NCET-08 0403), the Research Fund for the Doctoral Program of Higher Education of China(No. 20090075120007), the Shanghai Commitee of Science and Technology, China (No.09230500200), the Fundamental Research Funds forthe Central Universities of China (No.10D1 1308), the Key Special Program on the S&T for the Pollution Control and Treatment of WaterBodies (No.2008ZX07316-003) and the Shanghai Leading Academic Discipline Project (No.B604)."Correspondence should be adressed to Yong-Mei LI. Tel: 86-21-65982693; Fax: 86-21-65986313; E mail: liyongmei@tongji.edu.cnBiographical note of the flrst author;: Dr. Man-Hong HUANG, is an associate professor and fellow at the Collge of EnviromentalScience and Engineering, Donghua University, majoring in water pollution and b中国煤化工TYHCNMH Gb0Copyright o 2010by China CDC481HUANG ET AL.48o investigate the toxicity reduction potential in thissystem was operated in a room with a constantsystem. The effects of the hydraulic retention timetemperature of25 C.(HRT)， sludge retention time(SRT) and intermalrecycle ratio (IRR) on both toxicity and nutientCalculationsremoval were investigated. In addition, toluene wasThe pollutant concentrations in anaerobic, anoxic,added to assess the toxic-shock resistance of theand aerobic reactors were calculated according to Eq.biological treatment process.(1)-(3):MATERIALS AND METHODS,= C+RxCa(11+RLuminescence Bacterium Toxicity BioassayCa= 1+R)xC+rxC(21+R+rA 15-min standard luminescence bacteriumCg=C2(3toxicity bioassay was conducted according to theThe overall pollutant removal efficiency of thestandard methods of national environmentalA7/0 system was calculated according to Eq. (4).protection agency (NEPA)"3]. The freeze driedOverall pollutant removal efficiencymarine bacterium (Photobacterium phosphoreum)(%)=. Cx2-(Q -QJ)xC.-Q.xC，100% (4)and the testing instrument (toxicity analyzer modelCxQDXY-2) were purchased from the Institute of SoilScience, Academic Sciences, Nanjing PRC. ToxicityThe total percentage of pollutant removed fromwas measured using the DXY-2 instrument bythe influent was obtained by taking the sum of thequantifying the decrease in light emission from thepercentage of the pollutants removed by the anaerobic,bacteria that occurred in response to exposure of theanoxic, aerobic and settling reactors. These percentageswastewater to 3% NaCl solution for 15 min. Thewere calculated using Eq. (5)-(8), respectively:luminescent bacterium inhibition rate (LBIR) has%Anaerobic removalbeen shown to be an effective indicator of toxicity for(Cn-C)xQx(+R)x100%(5)all environmental samplesl14-16; therefore, it was used(C-C2)xQ+(C,-C)xQto express the toxicity of the wastewater in this study.%Anoxic removalChemical Analysis of Water Quality(Cn-C)x2x(l+R+) x100%0(6(C-C)xQ+(C. -C)xQwWater quality items including water temperature,%Aerobic removalpH, DO, BODs, COD, SS, NH4*N, TP, and TOC=- (Gg-C)xQx(l+R+) x100%were measured according to the standard methods of(C-C,)xQ+(C -C})xQ.the NEPAlS. TOC was measured by a total carbon%Stling removalanalyzer (TOC-Vcpn, Shimadzu Company). Gaschromatography (GC) was used for quantitative_C,x(Q+ RQ-Q)-C x(Q-Q)- RQCa(⑧)analysis of toluene. The GC detector used in the test(C-CJ)xQ+(C, -C)xQrwas an Agilent 6 890N (30.0 mx0.32 mmx0.25 μm,In the above equations, C; is the pollutant (COD,HP-5 column, with N2 as the carrier gas). The GCTP, TN, TOC) concentration in the influent; C1, C2,temperature program was 100 C for 1 min, afterC3, Ce are the pollutant (COD, TP, TN, TOC)which it was linearly ramped to 150 C at 2 C/min,concentrations in the effluent from the anaerobic,where it was held for 2 min.anoxic, aerobic, and settling reactors, respectively;Ce is the pollutant (COD， TP, TN, TOC)Operational Conditions of the Systemconcentration in the returm sludge; Ci, Cz, and CgThe system used in this study consisted of threeare the pollutant (COD, TP, TN, TOC) concentrationsin mixed liquors in the anaerobic, anoxic, and aerobicplexiglass complete-mixed reactors inseries.Specifically, the reactors consisted of an anaerobicreactors, respectively. Q and Qw are the influent flowreactor, anoxic reactor, and aerobic reactor withrate and waste sludge flow rate, respectively. R and reffective volumes of7 L, 7 L, and 21 L, respectively.are the recirculation ratios for activated sludge andThe influents of the lab-scale A/O process weremixed liquor, respectively.obtained from a local MWWTP in Shanghai, China.中国煤化工The seed stludge in the system was obtained from thereturned sludge of an existing pilot-scale A7/0MHCNMHGprocess treating municipal wastewater. The entireWhen' une system was operated steadily, the83TOXICITY REDUCTION OF MUNICIPAL WASTEWATER BY A7/0 PROCESSoperational parameters were changed one by one inremarkable effect on the adsorption,an attempt to determine the optimum operationalbiotransformation and decomposition of pollutants inconditions for reduction of the municipal wastewaterwastewater treatment plants'[1,17-18]toxicity. The returned sludge rate was maintained atTo investigate the effect of HRT on toxicity100% throughout the experiment.reduction, we kept the internal recycling ratio atThe Effect of Hydraulic Retention Time (HRT) on200% and increased the HRT by increasing the flowrate gradually. Six group experiments were conductedToxicity Reductionby increasing the HRT. The experimental results ofSeveral studies have shown that HRT could havethe entire system are shown in Table 1.TABLE 1Treatmeat Performance of the A/0 Process at Different HRTHRT of the Entire System, hPararnetersPeriormance6.08.010.01.5 14.019.5Average Removal Eficiency, %84.07.288.686.486.0NH4'NStandard Deviation3.4 2.64.10.63.01.91.090.42.092COD2.11.60.80.2.52:Average Removal Efficiency, %76.780.984.783.183.482.1LBIR4.9).3.9TABLE2Effet of HRT on the Removal of COD and LBIR in the Anaerobic Reactor of the A/O SystemHRT of Anaerobic Reactor, hParametersPerformance21.6 2.02.3 2.83.9Average Removal ffciency, %53.953.260.559.9.74.53..0Average F; Removal Eficiency, %3.12229.32..4TABLE3Effeet of HRT on the Removal of COD and LBIR in the Anoxic Reactor of the A7/0 SystemHRT of Anoxic Reactor, h.2.89.210.,.95..61.31.24.66:3.26.TABLE4Effeet ofHRT on the Rermoval of COD and LBIR in the Acrobic Reactor of the A7O SystemHRT of Aerobic Reactor, hn3.64.86.9 8.411.7Average Removal Eficiency,%24.9222 28.728.1中国煤化工Average Removal Eficiency,; %30.6MHCNMH G 21HUANG ET AL.48As ilustrated in Table 1, the change in HRT dideficiencies of TN and TP were severely infuenced1ot have a significant effect on the removalby the changes in SRT.performance of the overall process. When the HRT ofWhen the combined TN, TP and toxicity removalthe entire system increased from 6h to 19.5 h, theefficiencies were considered, an SRT for the systemaverage COD and NH4'-N removal efficienciesof 15 days was preferable. At this SRT, the COD, TN,ranged from 89%-92% and 84%-88%, respectively.TP and toxicity removal efficiencies were 88.2%,Additionally, the toxicity reduction efficiency68.0%, 74.6%, and 80.4%%, respectively (Fig.1).reached a stable high level (above 80%) when theThe Effect of Internal Recycle Ratio (RR) on ToxicityHRT of the entire system was greater than 8.0 h. .As shown in Table 2 - Table 4, the wastewaterReductiontoxicity was primarily reduced in the aerobic reactor,IRR values between 100% and 300% werewhere the LBIR reduction efficiency attained 40.7%recommended by Metcalf and Eddy for A/Oat an aerobic HRT of 6.9 h. The highest LBIRprocesses treating municipal wastewaterl9. Fourreduction fficiency in the anoxic reactor was 13.2%IRRs (0, 100%, 200%, 300%) were applied to A/Oat an anoxic HRT of 2.8 h, which was the lowestprocesses with an SRT of 15 days and a total HRT ofamong the three reactors.12.5 h. Mulkerrins found that the IRR increased fromThe Effect of Sludge Retention Time (SRT) on100% to 300%, leading to improved NO2-N removalin their systeml20). In agreement with their findings, aToxicity Reductionthree-fold increase in IRR was found to lead toIt was evident that a short SRT favoredNOx-N concentrations decreasing fom 12.8 mg:L' toP-removal; however, a short SRT was not good for9.4 mgL" in the clarified effluents in the presentnitrogen removal because the generation time ofstudy (Fig.2). .nitrifying bacteria is long. Therefore, the SRT should■a LBIR00be very carefully considered when designing a+ NH-N+CODwastewater treatment system.宫90LBIR - +COD + NH&N士TP-*-TN-米BOD,8S:100 r8090 t80-757060+6570.豆6040 t60豆0Intermal Recycle Ratio20 t50亩FIG 2. Performance ofA?/0 process at dfferent IRRsPerformance of the A/0 Process under Toluene122(26Shock LoadingSRT,dFIc.1. Removal performance of the A/O process atAccording to the results of our GC-MS analysisdiferent SRTsof the influents and effluents of several MWWTPs inDuring this stage, we maintained the intemalShanghai, China, toluene was widespread in therecycling ratio at 200%， the anaerobic hydraulicwastewater treated by these plants'I. The toxicretention time (HRT) at 2.8 h, the anoxic HRT at 2.8effects caused by the_ increase in the tolueneh, the aerobic HRT at 6.9 h and gradually changedconcentration of the A7O system might lead totheSRTfrom8dto26d.AsshowninFig.I,whendeterioration of sludge; therefore, toluene wasthe SRT increased from 8d to 26 d, the COD andselected as a typical toxicant in this study to analyzeNH4' N removal efficiencies were all greater thanits impact on reduction of toxicity in the A/O85% and 82%, respectively. Additinally, the TNprocess. The system was operated for two weeks forremoval eficiencies increased from 46.9% to 74.2%，each中国煤化工ig.3 shows thewhile the TP removal efficiencies dropped fromperforFuring the toxic80.5% to 42.7%. It was evident that the removal shock片CNMHG85TOXICITY REDUCTION OF MUNICIPAL WASTEWATER BY A30 PROCESS180zzza ToC，110口Co100160Toluene90140- + LBIR801207050。so0106C304020旨年旨Toluene Adition of 16.06 mg/LToluene Addition of 58.90 mg/LToluene Additio of 120.70 mgLFIG 3. Performance ofA7/0 process after addition of toluene at diferent concentrations.DISCUSSIONof sludge decay and desorption of toxicants from theshudge.The Effect of Hydraulic Retention Time (HRT) onThe Efect of Intermnal Recycle Ratio (IRR) on ToxicityToxicity ReductionReductionIn the anaerobic reactor, more than 50% of theCOD was removed, but the toxicity was reduced lessRecycling of the mixed liquor from the aerobicin this reactor, with a maximum of 26.5% occurringreactor to the anoxic reactor was beneficial to theat an anaerobic HRT of 2.8 h. This was likelyreduction of toxicity in wastewater. The toxicitybecause some of the refractory toxicants werereduction efficiency was highest at an IRR of 100%.decomposed and transformed into other types ofA further increase of IRR may not help remove moretoxicants in the anaerobic reactor. The highest LBIRtoxicants. It was particularly evident that the toxicityreduction eficiency in the anoxic reactor was 13.2%reduction did not improve as the IRR was increasedat an anoxic HRT of 2.8 h, which was the lowesttom 100% to 300%. In summary, the optimumoperation conditions of the A7/0 process for toxicityamong the three reactors.reduction were as follows: HRT=12.5 h, SRT=15 dThe Effect of Sludge Retention Time (SRT) onand IRR=100%. Under the above conditions, thremoval ratios of NH4 -N, COD, BODs and toxicitywere 90.0%, 80.0%, 81.2%, and 82.2%, respectively.In the SRT range of 8-20 d, an increase in SRTwas beneficial to toxicity reduction. Indeed, thePerformance of the A/O Process under Toluenetoxicity reduction eficiency reached its maximum ofShock Loading82.6% when the SRT was 20 d. However, when theSRT was longer than 20 d, the toxicity reduction中国煤化工ess could resistefficiency decreased, which may have been the resultthe toene.YHCNMHGHUANG ETAL.48Specifically, the addition of toluene at 16.06phosphorus removal: The effect of acetate addition. ProcessBiochem 43, 605-614.mgL, 58.90 mg/L, and 120.70 mg/L did not produce3. Bacza J A, Gabriel D, Lafuente J (2004). ffeet of internalgreat disturbances in the system, and the toluenerecycle on the nitrogen removal efficiency of anconcentration of the effluent was very low whenanaerobic/anoxic/oxic (AO) waslewater treatment plantcompared with that of the influents. Indeed, the system(WWTP). Process Biochem 39, 1615-1624.toxicity reduction efficiency was over 50%, even at a4. Satoshi Tsuneda, Takashi Ohno, Koichi Sojima, et al. (2006).Simultancous nitrogen and phosphorus removal usingtoluene influent concentration of 120.7 mgL'.denitrifying phosphate-accumulating organisms in a sequencingbatch reactor. 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Studies on the toxic efects ofhad significant efects on the performance of thepentachlorophenol on the biological activity of anaerobicA2/0 process. Based on an experiment in which theregranular sludge. J Environ Manag 88, 939-946.was a constant returned sludge ratio of 100%, the9. Nasu M, Goto M, Kato H (2001) Study on endocrine disruptingchemicals in wastewater treatment plants. Wat Sci Tech 4optimum conditions of the A/O process for101-108.municipal wastewater toxicity reduction should be an10.Doerger J U, Meier R A. Dobbs R A, et al. (2002). ToxicitySRT of 15 days, an anaerobic hydraulic retentionreduction evaluation at a municipal wastewater treatment plartime (HRT) of 2.8 h, anoxic HRT of 2.8 h, aerobicusing mutagenicity as an endpoint. Arch Environ ContamHRT of 6.9 h and IRR of 100%。Under the above11.OndaK. YangS Y, Miya A. et al. 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