Hydrolysisacidificationanddewaterabilityofwasteact

Hydrolysis,acidificationanddewaterabilityofwasteactivatedsludgeunderalkalineconditions:CombinedeffectsofNaOHandCa(OH)2GaoqiangSua,MingxinHuob,ZhiguoYuana,c,ShuyingWanga,YongzhenPenga,⇑aKeyLaboratoryofBeijingWaterQualityScienceandWaterEnvironmentRecoveryEngineering,EngineeringResearchCenterofBeijing,BeijingUniversityofTechnology,Beijing100124,ChinabSchoolofUrbanandEnvironmentalSciences,NortheastNormalUniversity,Changchun130024,ChinacAdvancedWaterManagementCenter,TheUniversityofQueensland,QLD4072,AustraliahighlightsCombineduseofNaOHandCa(OH)2enabledhighVFAproduction.CombineduseofNaOHandCa(OH)2enabledgoodsludgedewaterability.CombineduseofNaOHandCa(OH)2decreasedthecostsforVFAproduction.Ca2+mayinhibitproteinhydrolysisanddecreaseVFAproduction.TheNaOHtoCa(OH)2ratiodidnotexertinfluencesonsolubilisationofWAS.graphicalabstractarticleinfoArticlehistory:Received18December2012Receivedinrevisedform4March2013Accepted6March2013Availableonline13March2013Keywords:WasteactivatedsludgeVolatilefattyacidDewaterabilityMixedalkalineconditionabstractHydrolysis,acidificationanddewaterabilityofwasteactivatedsludge(WAS)wereinvestigatedatpH10controlledbytheadditionofNaOH,Ca(OH)2ortheirmixturesatvariousratios.SimilarefficiencyofWASsolublisationwasobservedinallcases,at38–40%.Highvolatilefattyacid(VFA)productionandgoodsludgedewaterabilitycouldnotbeachievedsimultaneouslybyaddingNaOHorCa(OH)2alone,butcouldbeachievedbyaddingmixturesofNaOHandCa(OH)2.VFAproductioninthecasewiththeadditionofCa(OH)2only(1201mg(COD)/L)waslowerthaninthecaseswiththeadditionofNaOHoritsmixtureswithCa(OH)2(1813–1868mg(COD)/L),andthelowerVFAproductionwithCa(OH)2additionalonecouldberelatedtothefactthatahigherconcentrationofCa2+wasreleasedintothefermentationliquid,whichlikelyinhibitedthehydrolysisprocessofprotein.Furthermore,addingmixturesofNaOHandCa(OH)2wasmoreeconomicalforVFAproduction.2013ElsevierLtd.Allrightsreserved.1.IntroductionTheactivatedsludgeprocessiswidelyusedworldwideformu-nicipalandindustrialwastewatertreatment.Organicpollutantsinwastewateraretransformedintobiomassorcarbondioxideintheprocess.Asaresult,alargeamountofwasteactivatedsludgeisproducedwithdisposalcostsaccountingfor20–50%ofcapitalandoperationcostsofwastewatertreatmentplants(WWTPs)(Kroiss,2004).SludgereductionisimportantforWWTPs.Intheactivatedsludgeprocess,carbonsourcessuchasvolatilefattyacids(VFAs)areessentialfornitrogenandphosphorusre-moval(ElefsiniotisandOldham,1994).However,carbonsourcesareoftennotadequateintheinfluent,andinsuchcasesexternalcarbonsourcesarerequiredtoenhancenitrogenandphosphorusremoval,whichcausesincreasesnotonlyinoperationcostsbutalsoinWASproduction(Gaoetal.,2011).Technologiesthatcansimultaneouslyrealizesludgereductionandregeneratecarbonsourcesforimprovingbiologicalnutrientremovalareindemand.0960-8524/$-seefrontmatter2013ElsevierLtd.Allrightsreserved.⇑Correspondingauthor.Tel./fax:[phone].E-mailaddresses:[e-mail](G.Su),[e-mail](Y.Peng).BioresourceTechnology136(2013)237–243ContentslistsavailableatSciVerseScienceDirectBioresourceTechnologyjournalhomepage:(Fengetal.,2009).However,hydrolysisratelimitstheacidificationprocessofWASbecauseproteinandcarbohydratearesurroundedbycellmembraneandcellwall.FermentingWASunderalkalineconditionsisapreferabletechnologyforWASreductionandcar-bonsourceproduction(Yuanetal.,2006).Alkalineconditionscandestructcellwall,andthusenhanceWAShydrolysis.Alkalineconditionscanalsoinhibittheactivitiesofmethanogenscomparedwithneutralandacidicconditions.ConsequentlyWASreductioncouldbeimprovedandmoreVFAcouldbeproduced.NaOHandCa(OH)2arethetwotypesofalkalithatwerewidelyusedforalka-linesludgetreatment.ThetypeofalkaliimpactssignificantlyonWAShydrolysis,acidificationanddewaterability(Kimetal.,2003).Goodsludgedewaterabilitycanbenefittheseparationoffermentationliquidfromsludgeandsludgereduction.WhiletheeffectsofNaOHandCa(OH)2onWAShydrolysisanddewaterabilityhavebeenreportedinliterature(Lietal.,2008;StuckeyandMcCarty,1984),thecombinedeffectsofNaOHandCa(OH)2onWAShydrolysis,acidificationanddewaterablityhavenotbeenstudiedtodatetothebestoftheauthor’sknowledge.TheobjectiveofthispaperwastoinvestigatehowWAShydrolysis,acidificationanddewaterablitywouldbeaffectedbycombineduseofNaOHandCa(OH)2forthealkalinetreatmentofWAS.WealsoaimtoidentifysuitableNaOHandCa(OH)2ratiosthatenablebothgoodacidificationandgoodsludgedewaterability.2.Methods2.1.SourceofWASTheWASusedwaswithdrawnfromapilot-scalesequencingbatchreactor(SBR)(8.8m3)operatedinourlaboratoryperformingbiologicalorganiccarbonandnitrogenremovalfromdomesticwastewater.Sludgewasremovedattheendofthesettlingphase.ThemaincharacteristicsoftheWASwereasfollows:pH6.87±0.02,totalsuspendedsolids(TSS)7139±172mg/L,volatilesuspendedsolids(VSS)6155±149mg/L,totalchemicaloxygende-mand(TCOD)8884±123mg/L,solublechemicaloxygendemand(SCOD)34±2mg/L,so