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High-ratepartialnitrificationtreatmentofrejectwaterasapretreatmentforanaerobicammoniumoxidation(anammox)LiZhanga,⇑,JiachunYanga,DaisukeHiraa,TakaoFujiib,KenjiFurukawaaaGraduateSchoolofScienceandTechnology,KumamotoUniversity,2-39-1Kurokami,Kumamoto860-8555,JapanbDepartmentofAppliedLifeScience,FacultyofEngineering,SojoUniversity,4-22-1Ikeda,Kumamoto860-0082,JapanarticleinfoArticlehistory:Received8September2010Receivedinrevisedform28November2010Accepted1December2010Availableonline7December2010Keywords:PartialnitrificationRejectwaterDOconcentrationAnammoxAlkalinityabstractInthisstudy,alab-scaleswim-bedpartialnitrificationreactorwasdevelopedtotreatammonium-richrejectwatertoachieveanappropriateNO2-N=NHþ4-Nmixturethatcouldserveasapretreatmentforanaerobicammoniumoxidation(anammox).StrictlycontrollingtheDOconcentrationwasadoptedasthemainoperationalstrategy.Inaddition,theinfluentconcentrationsofinorganiccarbon/ammoniumðIC=NHþ4Þandalkalinity/ammoniumðAlk=NHþ4Þthatwereapproximately0.8and4.8,respectively,wereregardedasthesuitableratiosforthesteadyandhigh-rateoperationofthereactorinthisstudy.Whenrejectwaterthatwasnotdilutedwasintroducedtothissystem,themaximumnitrogenloadingratewas5.9kg-N/m3/day,theammoniumconversionratewas3.1kg-N/m3/day,andtheeffluentNO2-N/(NO2-N+NO3-N)percentageratiowasover99.9%.Furthermore,DNAanalysisconfirmedtheexistenceofAOB,whichwasresponsibleforthestableperformancethatwasachievedinthePNreactor.CrownCopyright2010PublishedbyElsevierLtd.Allrightsreserved.1.IntroductionNitrogenpollutionisanincreasinglyimportantglobalissuebe-causeithasmultipleimpactsonterrestrial,aquaticandatmo-sphericenvironments.Nitrogenfromwastewatercanberemovedbyavarietyofphysicochemicalandbiologicalprocesses,butbiologicalprocessesarepreferredbecausetheyareusuallymoreenvironmentallyfriendly(Yangetal.,2010b).However,inmanyinstances,thebenefitsfromreusingeithermunicipaloragri-culturalwastewaterhavebeenhinderedbythelackofacost-effec-tiveandenergyefficientprocess.Recently,considerableattentionhasbeendirectedtowardanovelbiologicalprocess,anaerobicammoniaoxidation(anammox).Theanammoxprocessisanovel,environmentalfriendly,cost-effectivetechnologythathasahighnitrogenremovalpotential(Nietal.,2010).Partialnitrification(PN)canproduceasuitableinfluentforananammoxreactortoefficientlyremoveNHþ4-Nfromrejectwater.Inthisprocess,NHþ4-NisoxidizedtoNO2-NratherthanNO3-N,whichsaves25%oftheoxygenthatisneeded.TheapplicationofPNpriortoanammoxprovidesanewapproachfornitrogenremoval,therebyresultinginafurtherreductionofen-ergyandcarbondosage.AkeystepintheimplementationofthePNprocessistheprep-arationofsuitableconditionsforammonia-oxidizingbacteria(AOB)andtheintroductionofinhibitoryconditionsfornitriteoxi-dizingbacteria(NOB).Severaleffectivemethodshavetobeintro-ducedtosuppresstheoxidationofNO2-NtoNO3-N,includinginhibitionbyfreeammonium(FA),temperatureelevation,andthesuppressionofthedissolvedoxygen(DO)concentrationinthereactor(Philipsetal.,2002).Anelevatedtemperature(above35C)andpH(above7)couldenableAOBtopredominateoverNOB(KhinandAnnachhatre,2004).OperationatalowDOlevel,between0.7and1.4mg/LwillalsomoreeffectivelysuppresstheactivityofNOB(Ruizetal.,2003).DOconcentrationisdifficulttobecontrolledandmaintained,andbothaerationsystemsandaer-ationmodelswouldinfluencePNgreatly.Inaddition,increasingthepHisalsoimportantformaintainingacertainamountofalka-linityinthereactor,whichcanreducerisksinPNoperation.Inthisstudy,theDOconcentrationinaPNreactorwasstrictlycontrolledtofavorNO2-NaccumulationaswellastoinhibitNO3-Nproduction.Inaddition,tosafelyavoidthepotentialmalfunctionbypumprunningduringthereal-timepHcontrolprocess,theinfluentalkalinitywasregulatedinsteadofusingacidandalkalin-itypumps,inthecontinuous-runningPNreactor.Furthermore,DNAanalysiswasusedtoconfirmtheco-existenceofbacteriainthemicrobialcommunity.2.Method2.1.ExperimentalsetupandmicroorganismsAlab-scaleswim-bedreactorwithbiofringematerialasthebio-masscarrier(BF;acryl-fiberbiomasscarrier;NETCo.Ltd.,Hyogo)0960-8524/$-seefrontmatterCrownCopyright2010PublishedbyElsevierLtd.Allrightsreserved.doi:10.1016/j.biortech.2010.12.008⇑Correspondingauthor.E-mailaddress:zhangli19821115@yahoo.com.cn(L.Zhang).BioresourceTechnology102(2011)3761–3767ContentslistsavailableatScienceDirectBioresourceTechnologyjournalhomepage:(2010a)hadprovidedade-taileddescriptionofthepartialnitrification(PN)reactor.Theseedsludgeinthisstudywascollectedfromtworeactors,yieldinganinitialmixedliquorsuspendedsolids(MLSS)of0.8g/L.Forthepur-poseofacceleratingthestartupspeedofthePNreactorinthisstudy,partoftheenrichedsludgewasdirectlyobtainedfromanunder-runningswim-bedPNreactor,feedingwithrejectwater(Yangetal.,2010a).Butinordertoensuretheswim-bedPNreac-torrunnormallyaseverbefore,onlylittleamountoftheenrichedsludgewastakenfromthatreactor(onlyaccountingforabout30%oftheMLSS).Theotherpartoftheseedsludge(accountingfor70%oftheMLSS)wastakenfromalab-scalefill-drawactivateds