influenceofhighorganicloadingonCODremovala

ENVIRONMENTALENGINEERINGSCIENCEVolume25,Number9,2008©MaryAnnLiebert,Inc.DOI:10.1089/ees.2007.0071InfluenceofHighOrganicLoadingRatesonCODRemovalandSludgeProductioninMovingBedBiofilmReactorAhmetAygun,BilgehanNas,AliBerktay*DepartmentofEnvironmentalEngineeringSelcukUniversity,Campus42031Konya,TurkeyReceived:March15,2007Acceptedinrevisedform:June16,2007AbstractAmovingbedbiofilmreactor(MBBR),wherebiomassisattachedtosmallcarrierelementsthatmovefreelyalongwiththewaterinthereactor,hasbeentestedfororganicmatterremovalatfivedifferentorganicload-ingrates.Alab-scalereactorwithavolumeof2Lwasbuiltandfedcontinuouslywithsyntheticwastewater.ThereactorwasfilledwiththeKaldnesbiomediaK1whichisusedinthepatentedKaldnesMovingBedTMbiofilmprocessat50%ofthevolumeofemptyreactor.Hydraulicretentiontimes(HRT)inthereactorandinthesettlerwereadjustedtobetween8and4hours,respectively.Astart-upperiodofabout4weeksforbiofilmgrowthonthecarrierwasfollowedby10weeksoftestingperiod.Bychangingthewastewatercomposition,theoperationofthesystemwasadjusted,oneaftertheother,tofivedifferentorganicloadingrates:6,12,24,48and96gCOD/m2.d.Organicremovalefficiencydecreasedwithincreasingorganicloadingrate,rangingfrom95.1%,94.9%,89.3%,68.7%and45.2%astheorganicloadingratewasincreasedform6to96gCOD/m2.d.IntheMBRRreactor,thebiofilmreachedanaverageconcentrationof3.28kgTSS/m3atthehighestorganicloadingrate.TheratiobetweentheTSSproductionandthetotalCODremovalwas0.12kgTSS/kgtotalCODataninfluenttotalCODof500mg/l.Keywords:wastewatertreatment,movingbedbiofilmreactor,organicloadingrate,CODremoval,sludgepro-duction,biomassyield1311IntroductionThepatentedmovingbedbiofilmreactor(MBBR)wasde-velopedinScandinaviainthelate1980sbytheNorwe-giancompanyKaldnesMiljØteknologi(KMT),incoopera-tionwiththeSINTEFresearchorganization.Presently,therearemorethan400large-scalewastewatertreatmentplantsoperatingin22differentcountriesoftheworldbasedonthisprocess.Inadditionthereareseveralhundredsmall,on-sitetreatmentunitsbasedontheMBBR(Rustenetal.2006).TheKaldnesMBBRisacompletelymixedcontinuouslyoperatingbiofilmreactorwherethebiomassisgrownonsmallcarrierelementsthatmovealongwiththewaterinthereactor.TheinterestforMBBRisjustifiedbythefollowingadvantages:highsludgeage,nosludgerecycling,andlessbulkingproblems.Inthecaseofanupgradeinexistingplant,theMBBRsolutiondoesnotincreaseheadlosssignificantly,allowsacontinuousfeed,doesnotpresentcloggingprob-lemsanddoesnotrequirebackwashing.MBBRsallowap-plyinghigherloadscomparedtothoseappliedtothecon-ventionalactivatedsludge,incasethespecificsurfaceissuf-ficientlyhigh(Andreottolaetal.,2002;Andreottolaetal.,2003;Rustenetal.,2006).Thebiofilmcarrierelementsaremadeofpolyethylene(density0.92–0.96g/cm3)andshapedlikesmallcylinderswithacrossinsidethecylinderandlongitudinalfinsontheoutside.Inordertokeepthebiofilmcarriersinthereactor,asieveisplacedattheoutletofthereactor.Thefillingratioandthespecificareaofthebiofilmcarriersarethetwomaindesignparameters.Thefillingratiorangesfrom30–70%ofthetotalreactorvolume.Ødegaard(2000)recommendsthefillingfractionstobeunder70%forthecarriersthecarrierstobefree.MBBRshavealreadybeenusedinthetreatmentofdairywastewater(Rustenetal.,1992;Andreottolaetal.,2002),for-estindustrywastewater(DalentoftandThulin,1997),cheesefactorywastewater(Rustenetal.,1996),newsprintmillwastewater(Broch-Dueetal.,1997),thermomechanicalpulpingwhitewater(Jahrenetal.,2002),municipalwaste-water(Ødegaardetal.1993;OrantesandGonzález-Mar-tinez,2002),andfornitrification(Rustenetal.,1995;Walen-deretal.,1997)anddenitrification(Rustenetal.,1995;Aspegrenetal.,1998;Maureretal.,2001;WalenderandMat-tiasson,2003).*CorrespondingAuthor:Prof.AliBerktay(MSc.,Ph.D.Eng.)De-partmentofEnvironmentalEngineering,Campus,SelcukUniver-sity,42031,Konya-Turkey.Phone:90-332-2232093Fax:90-332-2410635;E-mail:[e-mail]pgradingcurrentwastewatertreatmentsystems.Manystudiesregardingsuccessfuloper-ationfornewwastewatertreatmentplantsandupgradesofexistingwastewatertreatmentplantshavebeenreported(Ødegaardetal.,1993;Hemetal.,1994;Orantesetal.,2002;DaudeandStephenson2003;Andreottolaetal.,2003).An-dreottolaetal.(2000)foundthathydraulicretentiontime(HRT)affectedtheCODremovalinMBBRprocessesandsuggestedthattheHRTshouldbehigherthan5h.AnotherstudywasperformedbyAndreottolaetal.,(2003),inwhichtheyevaluatedtheapplicationofMBRRsystemfortheup-gradingofanoverloadedMWWTP.Apreliminaryexperi-mentationatpilot-scalewascarriedoutinordertoevaluatetheefficiencyofthesystemintheremovaloforganicmat-terusingahighloadedMBBR.KMTplasticmediawasap-pliedwithafillingratioof50%.Theappliedsurfaceloadsrangedbetween5.4and32gtotalCOD/m2.d.Withtherisingcostsofsludgedisposal,theminimizationofsludgeproductionhasbecomeincreasinglyimportant.Theexpenseofexcesssludgetreatmenthasbeenestimatedtobe50–60%ofthetotalcostofmunicipalwastewatertreat-ment.Therefore,modificationoftheaerobictreatmentpro-cessinordertoreducebiosolidsproductionispromising(Kulikowskaetal.2007).ThemainobjectivesofthisresearchweretoinvestigateCODremovalefficie