ModelingthePAOGAOcompetition

ModelingthePAO–GAOcompetition:Effectsofcarbonsource,pHandtemperatureCarlosM.Lopez-Vazqueza,f,AdrianOehmenb,ChristineM.Hooijmansa,DamirBrdjanovicc,HuubJ.Gijzena,d,ZhiguoYuane,MarkC.M.vanLoosdrechtf,*aDepartmentofEnvironmentalResources,UNESCO-IHEInstituteforWaterEducation,Wesvest7,2611AXDelft,TheNetherlandsbCQFB/REQUIMTE,ChemistryDepartment,FaculdadedeCieˆnciaseTecnologia,UniversidadeNovadeLisboa,2829-516Caparica,PortugalcDepartmentofUrbanWaterandSanitation,UNESCO-IHEInstituteforWaterEducation,Wesvest7,2611AXDelft,TheNetherlandsdUNESCOOffice,Jakarta,UNESCOHouse,Jl.Galuh(II)No.5,KebayoranBaru,Jakarta12110,IndonesiaeAdvancedWastewaterManagementCentre(AWMC),TheUniversityofQueensland,St.Lucia,Queensland4072,AustraliafDepartmentofBiotechnology,DelftUniversityofTechnology,Julianalaan67,2628BCDelft,TheNetherlandsarticleinfoArticlehistory:Received13July2008Receivedinrevisedform6October2008Accepted7October2008Publishedonline1November2008Keywords:Enhancedbiologicalphosphorusremoval(EBPR)MetabolicmodelingMicrobialcompetitionVolatilefattyacids(VFA)Poly-b-hydroxyalkanoates(PHA)DefluviicoccusvanusabstractTheinfluenceofdifferentcarbonsources(acetatetopropionateratios),temperatureandpHlevelsonthecompetitionbetweenpolyphosphate-andglycogen-accumulatingorganisms(PAOandGAO,respectively)wasevaluatedusingametabolicmodelthatincorporatedthecarbonsource,temperatureandpHdependencesofthesemicroorgan-isms.ThemodelsatisfactorilydescribedthebacterialactivityofPAO(Accumulibacter)andGAO(CompetibacterandAlphaproteobacteria-GAO)laboratory-enrichedculturescultivatedonpropionate(HPr)andacetate(HAc)atstandardconditions(20CandpH7.0).Usingthecalibratedmodel,theeffectsofdifferentinfluentHActoHPrratios(100–0,75–25,50–50and0–100%),temperatures(10,20and30C)andpHlevels(6.0,7.0and7.5)onthecompetitionamongAccumulibacter,CompetibacterandAlphaproteobacteria-GAOwereevaluated.ThemainaimwastoassesswhichconditionswerefavorablefortheexistenceofPAOand,therefore,beneficialforthebiologicalphosphorusremovalprocessinsewagetreatmentplants.Atlowtemperature(10C),PAOwerethedominantmicroorganismsregardlessoftheusedinfluentcarbonsourceorpH.Atmoderatetemperature(20C),PAOdominatedthecompetitionwhenHAcandHPrweresimultaneouslysupplied(75–25and50–50%HActoHPrratios).However,theuseofeitherHAcorHPrassolecarbonsourceat20CwasnotfavorableforPAOunlessahighpHwasused(7.5).Meanwhile,athighertemperature(30C),GAOtendedtobethedominantmicroorganisms.Nevertheless,thecombinedpresenceofacetateandpropionateintheinfluent(75–25and50–50%HActoHPrratios)aswellasahighpH(7.5)appeartobepotentialfactorstofavorthemetabolismofPAOoverGAOathighersewagetemperature(30C).ª2008ElsevierLtd.Allrightsreserved.*Correspondingauthor.Tel.:þ31(0)152781618;fax:þ31(0)152782355.E-mailaddresses:[e-mail],[e-mail](M.C.M.vanLoosdrecht).Availableat–seefrontmatterª2008ElsevierLtd.Allrightsreserved.doi:10.1016/j.watres.2008.10.032waterresearch43(2009)450–4621.IntroductionInthelastdecades,enhancedbiologicalphosphorusremoval(EBPR)inactivatedsludgesystemshasbecomeawidelyappliedwastewatertreatmentprocess.Bydirectingtheinfluent(usuallyrichinreadilybiodegradableorganicmattersuchasvolatilefattyacids(VFA))totheanaerobicphaseandrecirculatingtheactivatedsludgethroughanaerobicandanoxic/aerobicconditions,theEBPRprocessconfigurationpromotestheenrichmentoftheactivatedsludgesystemwithpolyphosphate-accumulatingorganisms(PAOs)(Oehmenetal.,2007a).Whenoperatedsuccessfully,theEBPRprocesscanbeaninexpensiveoptiontoreachrelativelyhighphosphorusremovalefficiency(effluentphosphorusconcentrationslessthan1mg/L).However,undercertaincircumstancestheEBPRsystemmayexperienceprocessupsetsanddeteriorationduetofactorsthatarenotcompletelyunderstood(Oehmenetal.,2007a).Inordertofindpossibleexplanations,differentstudieshavelinkedtheappearanceofglycogen-accumulatingorganisms(GAOs)withthedeterioration,suboptimalopera-tionandevenfailureoftheEBPRprocessperformance(CechandHartman,1993;Satohetal.,1994;Saundersetal.,2003).FromaphosphorusremovalperspectiveGAOareseenasundesirablemicroorganismssincetheydonotcontributetothebiologicalP-removalprocessbutcompetewithPAOforthesamecarbonsource(VFA).Inthepursuitforcontrolstrategiestosuppresstheprolif-erationofGAO,certainenvironmentalan-doperationalconditionshavebeenidentifiedaskeyfactorstounderstandthecompetitionbetweenPAOandGAO:typeofVFApresentintheinfluent(e.g.acetateorpropionate)(Pijuanetal.,2004;Oehmenetal.,2005a,2006a),pH(Filipeetal.,2001c;Oehmenetal.,2005c),temperature(WhangandPark,2006;Lopez-Vazquezetal.,2008b)andthephosphorus(P)toVFAratio(Liuetal.,1997).Nevertheless,littleisknownabouttheeffectsthatthecombinationofthesefactorsmayhaveonthePAO–GAOcompetition.Nowadays,mathematicalmodelinghasbecomeaninte-gralpartofbiologicalwastewatertreatment,oftenforopti-mizationandpredictionofprocessperformance,andasasupportingtoolfordesign.Recently,modelingtechniqueshavealsobeenappliedtoobtainamoreaccurateevaluationandunderstandingoft