Functionofselfformingdynamicmembrane

Availableat’determinationbymicroelectrodeXiao-HongZhou,Han-ChangShi,QiangCai,MiaoHe,Yin-XiWuDepartmentofEnvironmentalScienceandEngineering,TsinghuaUniversity,Beijing100084,ChinaarticleinfoArticlehistory:Received3October2007Receivedinrevisedform29December2007Accepted1January2008Availableonline5January2008Keywords:Self-formingdynamicmembraneMicroelectrodeBiokineticparametersBio-foulingabstractTheself-formingdynamicmembranecoupledbioreactor(SFDMBR),whichusescoarsepore-sizedmaterialtoseparatesolidsandliquidsinabioreactor,hassomeadvantagescomparedwithmembranebioreactor(MBR)usingmicro-/ultra-filtrationmembranessuchaslowmodulecostandhighflux.Inthisstudy,weinvestigatethemicrobialactivitychangeofaself-formingdynamicmembrane(DM)duringitsbio-foulingprocessbyamicroelec-trodeforO2.Atahighfluxof40L/m2h,thedissolvedoxygenwasdeterminedtobedepletedatthedepthof1.5–2.0mmintheself-formingDM.Basedonthedissolvedoxygenconcentrationprofilesintheself-formingDM,areliableandsimplemodelandcomputationalprocedureweredevelopedtoestimatethebiokineticparametersintheself-formingDM.Sensitivityanalysisofthemodelrevealedthatthedissolvedoxygenprofilesaresufficientlysensitivetothemaximumspecificratesofoxygenuptake(q_max;20),whichwerecomputedtobewithintherangeof3.8–11.1mgO2/gSSh.q_max;20decreasedsharplyinthefirst5dayswiththedevelopmentofthebio-foulingprocessinthesurfacecakelayeroftheself-formingDMandthenreachedarelativelysteadystateafterwards.TheMonodhalf-saturationcoefficientforoxygen(Ko)wascomputedtobeintherangeof0.16–0.75mgO2/L.Insummary,theresultsgavenewexperimentalevidenceonthechangeofmicrobialactivityintheself-formingDMduringitsbio-foulingprocess.&2008ElsevierLtd.Allrightsreserved.1.IntroductionThemembranebioreactor(MBR),whichusesmicro-/ultra-filtrationmembranestoseparatesolidsandliquidsinthebioreactor,hasattractedincreasinginterestinthefieldofwastewatertreatmentduetoitsreliabilityandhighefficiency,forexample,initsgoodrejectionofSS(effluentSSisclosetozero),highbiomassconcentration,smallfootprint,andlowsludgeproduction(WilliamsandPirbazari,2007;Holakooetal.,2007).However,thehighcostofmembranesandthepotentialrapidlossofperformanceduetomembranefoulingaretwomajordrawbacks.Furthermore,itswidespreadapplicationcanbelimited.Theself-formingdynamicmem-branecoupledbioreactor(SFDMBR)isanewmembranetechnologyusingacoarsepore-sizedmaterialmodule,suchasmesh,non-wovenfabric,filter-cloth,etc.,insteadofmicro-filtrationandultra-filtrationtoseparatesolidsandliquidsinthebioreactor(FanandHuang,2002;ChuandLi,2006;Seoetal.,2002).SFDMBRhasalowmodulecostandahighfluxcomparedtoMBRusingmicro-/ultra-filtrationmembrane.Incontrasttothemicro-/ultra-filtrationMBR,sincetheparticlesizeofactivatedsludgeisusuallysmallerthantheporesizeofthecoarsepore-sizedmaterial(about5–200mm),theself-formingdynamicmembrane(DM)formedonthesurfaceandintheporesofthematerialduringthecross-flowfiltrationisdesiredandplaysanimportantroleinsteadoftheprimarymembraneinseparation.UnliketheprecoatedDM,whichisproducedbyexploringaporousmediumtoasolutionofoneARTICLEINPRESS0043-1354/$-seefrontmatter&2008ElsevierLtd.Allrightsreserved.doi:10.1016/j.watres.2008.01.004Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](H.-C.Shi).WATERRESEARCH42(2008)2369–2376ormorespecificcolloidalcomponentsorparticlereagentsbeforeutilizationforfiltration(Al-MalackandAnderson,1996;Yeetal.,2006),theself-formingDMiscreatedwhencross-filteringthesubstancesintheactivatedsludgemixedliquorinSFDMBR;thereforeitperformssolid–liquidsepara-tionefficiently,andalsoitsbiologicalreactioncannotbenegligible(Wuetal.,2005).Theself-formingDMcanbeformedandre-formedbyanewdepositedlayer.Thus,thecostsofpurchasingandphysicallyreplacingnewmembranearespared.OurpreviousstudydemonstratedthatSFDMBRhadgoodperformanceinpollutantremovalandSSrejectionevenatahighmembranefluxof40L/m2h(Wuetal.,2004).Theself-formingDMformedinthereactorcanhaveathicknessofseveralmillimeterstoseveralcentimeters.Theexternallayeronthesurfaceofthematerial,whichcanberemovedeasilybymechanicalaction,isthecakelayer,whiletheinternallayeronthesurfaceandintheporesofthecoarsepore-sizedmaterial,whichadherestightlytothesupportingsurfaceandcanhardlybeflushed,isthegellayer.KuberkarandDavis(2000)pointedoutthattheexternalcakeofrejectedparticlesplayedanimportantroleinfiltrationprocesses,ofteninfluencingthepermeationratesofallspecies.InFanandHuang’s(2002)study,thecakelayerwasalsofoundtocontributemostofthefiltrationresistancetotheself-formingDM.Therefore,theinternalinvestigationoftheself-formingDM,especiallyinthecakelayer,duringitsbio-foulingprocessismeaningful.Toourbestknowledge,researchesontheself-formingDMactivitychange,whichcorrespondinglycorrelatestobioki-neticparameterschangeduringitsbio-foulingprocess,arerare.Inpractice,thebiokineticparametersinbiofilmsystemsareparticularlydifficulttobemeasuredbecauseofthekineticsofdiffusionlimitationandthedifficultyofreplicat