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Foundationitem:TheResearchandDevelopmentProjectofChinaStateDepartmentofConstruction(No.04-02-166),theChinaPostdoctoralScienceFoundation(No.2003034076)andtheFoundationofStateKeyLaboratoryofEnvironmentalSimulationandPollutionControlArticleID:1001-0742(2005)04-0557-05 CLCnumber:X703 Documentcode:ABiologicalpretreatmentofYellowRiverwaterXIEShu-guang1,TANGXiao-yan1,WUWei-zhong1,WENDong-hui1,WANGZhan-sheng2(1.DepartmentofEnvironmentalSciences,CollegeofEnvironmentalSciences,PekingUniversity,Beijing100871,China.E-mail:xiesg@pku.edu.cn;2.DepartmentofEnvironmentalScienceandEngineering,TsinghuaUniversity,Beijing100084,China)Abstract:Bio-ceramicfilter(BF)andmoving-bedbiofilmreactor(MBBR)wereusedforbiologicalpretreatmentofYellowRiverwaterinthisstudy.TheBFonlyhadslightadvantageoverMBBRforTOCandammoniaremoval.However,likeUV254,theaverageremovalrateofTHMFPintheBFwasmuchhigherthanthatintheMBBR.UV254removaldidnotshowobviouscorrelationwithtrihalomethaneformationpotential(THMFP)removal.HexachlorocyclohexanecouldbeeffectivelyremovedinbothBFandMBBR.AsfordiatomandcyanobateriaremovaltheMBBRhadbetterperformancethantheBF,whichwascontrarytotheaveragechlorophyll-a(Chl-a)removalrate.TheproposalwasmadeinthisstudythatbiologicalflocculationandsedimentationofsloughedbiofilmshouldplayamoreimportantroleonalgaeremovalintheMBBRthanintheBF.TheBFandMBBRcouldeffectivelyremovemicrocystins.Moreover,MBBRcouldbeapromisingtechnologyforbiologicalpretreatment.Keywords:bio-ceramicfilter(BF);moving-bedbiofilmreactor(MBBR);YellowRiver;biologicalpretreatmentIntroductionYellowRiverisoneofthelargestdrinkingwatersourcesinChinawhichisnowfacedwithseriousproblemscausedbypollutionandeutrophication.Thetapwaterqualityofmostofwatersupplysystems,whichabstractwaterfromYellowRiver,cannotmeetincreasinglystringentdrinkingwaterqualitycriteriaduetolimitationofconventionaldrinkingwatertreatment.Themainprocessesoftheconventionaldrinkingwatertreatmentconsistofsedimentation,coagulationflocculation,phaseseparation,rapidsandfiltration,anddisinfection,forremovingturbidity,colorandpathogens.However,itcannotremovetheammonia,THMprecursors,andvarioussyntheticorganicchemicals(SOCs)effectively,sothatadvancedwatertreatmenthastobeconsideredfortheproductionofsaferandcleanerdrinkingwater.Biologicalpretreatmentprocess(priortoconventionaltreatmentchain)isconsideredasaneconomicandeffectivetreatmentprocesstoremovepollutantsfromrawwater.ThekindofadvancedprocesshasbeenwidelystudiedinEuropeanandAsiancountries.Amongvariousbioreactorsforpretreatment,thebiologicalcontactoxidationreactor(BCOR)andBFhavebeenmostwidelystudiedinChina,especiallyinthesouthernregions(Wang,1999).Theyhavemanyadvantagessuchasimprovementofsequentialtreatmentchain,reductionofchlorinedemand,lessproductionofTHMs,andincreaseofbiologicalstabilityoffinishedwater(Bruce,1989).Unfortunately,thedataconcerningbiologicalpretreatmentofYellowRiverwaterhasnotbeenavailableuptodate.MBBRisaninnovativefixedbiofilmreactor,whichhasgainedincreasingattentionfromwastewatertreatmentindustry.Ithasbeensuccessfullyappliedforfull-scaletreatmentofmunicipalandindustrialwastewaters.MBBRisacontinuouslyoperatingnon-cloggablebiofilmreactorwithnoneedforbackwashinglowhead-lossandhighspecificbiofilmsurfacearea.Thiscanbeachievedbyhavingthebiofilmgrowonsmallcarrierelementsthatmovealongwiththewaterinthereactor.Themovementisnormallycausedbyaerationintheaerobicversionofthereactors(Pastorelli,1997;Rusten1996;Aspegren,1998).However,thisinnovativebiofilmreactorhasnotbeenintroducedforthepretreatmentofdrinkingwater.TheobjectiveofthisstudywastoinvestigatethefeasibilityofbiologicalpretreatmentofYellowRiverwater.Theremovalratesofvariouspollutantswereevaluatedinthisstudy,whichcouldbeveryusefulandfundamentaldataforthedesignoffuturewatersupplyprojecttakingYellowRiverwaterasrawwatersource.1 Materialsandmethods1.1 ExperimentalsetupTwokindsofbioreactors:BFandMBBR(Fig.1andFig.2)wereusedtoinvestigatethefeasibilityofbiologicalpretreatmentofYellowRiverwater.TheBFwascylindermadeofplexiglasandwithdimensionsof3mhighand0.5mofinsidediameter(Fig.1).Thefilterwasfilledwithceramicparticlesupto2mdepth.Ceramicparticleshadanaveragediameterof3—5mm,aporosityof0.09,adensityof1.56gcm3,andaspecificsurfaceareaof2.5m2cm3.Inletsforairinfluentwerelocatedatthebottomofthereactors.Liquidandgasphasesflowedupthroughthefilterincounter-currentmode.Fig.1 ExperimentalsetupofBFprocessTheMBBRwascuboidmadeofsteelwithatotalliquidvolumeof6m3.Thereactorwasfilled50%LThollowballmedia(density0.98gcm3,diameter100mm,specificsurfacearea360m2cm3),occupying11.5%oftheJournalofEnvironmentalSciences Vol.17,No.4,pp.557—561,2005ISSN1001—0742CN11—2629XFig.2 ExperimentalsetupofMBBRprocessreactors.Mixingandaerationwereprovidedbypressurizedairthroughaeratorsinthebottomofthereactor.ThestudywasperformedinShiyuanWaterWorksinZhengzhouCityintheyearof2004.Thetworeactorswerefedwiththesamerawwater,whichwasYellowRiverwateraftersedimentationforsandremoval.TheinfluentflowforBFandMBBRwas1and4m3hrespectively.ThepHvaluesofrawwaterrangedbetween8.0—8.5.