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AnammoxgranulesformationandperformanceinasubmergedanaerobicmembranebioreactorZiyinLi,XiaochenXu⇑,BingShao,ShuShenZhang,FengLinYang⇑KeyLaboratoryofIndustrialEcologyandEnvironmentalEngineering,MinistryofEducation,SchoolofEnvironmentalScienceandTechnology,DalianUniversityofTechnology,Dalian116024,PRChinahighlightsAnammoxgranuleswereachievedbyselectingapropershearstressintheSAnMBR.ThegranulesreachedaninfluentTNof4.1g/LwithTNremovalefficiencyof88%.TheformedAnammoxgranulesreachedadoublingtimeofaround6.9days.NO2-NdegradationkineticsofAnammoxbiomasswasobtained.Membraneoperationcircleprolongedwithgranulesizegrowingfrom287to896lm.articleinfoArticlehistory:Received26December2013Receivedinrevisedform19March2014Accepted17April2014Availableonline9May2014Keywords:AnammoxGranulesSAnMBRBiodegradationkineticsMembranefoulingabstractAnaerobicammoniumoxidation(Anammox)granuleswiththemaximumspecificAnammoxactivity(SAA)of2.14kgN/kgVSSd,theshortdoublingtimeof6.9daysandthemaximumendurableNO2-Ncon-centrationof130mg/Lweresuccessfullyformedinacontinuouslyfedandcompletelymixingsubmergedanaerobicmembranebioreactor(SAnMBR).Withspecificinputpowerrangingfrom0.08to0.02kW/m3,meanparticlesize(volume-weightedmean)oftheAnammoxflocsdidnotchangealot.Withaspecificinputpowerof0.003kW/m3,themeanparticlesizeincreasedrapidlyfrom180lmoftheflocsto863lmoftheformedgranulesin90days.Withmaximuminfluenttotalnitrogen(TN)upto4.1g/L,astablenitrogenremovalefficiencyof88%wasaccomplishedbytheformedgranules.ThenitritedegradationkineticswasalsoinvestigatedanditshowedthattheformedAnammoxgranulesreacheditsmaximumactivityat30mgNO2-N/Lbutwasstronglyinhibitedat150mgNO2-N/L.Withgranulesizeincreasingfrom287to896lm,themembraneoperationcircleprolongedby2–2.3timesduetothereliefofmem-branefouling.ThecultivatedAnammoxgranuleswithhighactivityandshockresistancecapacity,fastgrowthrateandrelievedmembranefoulingshowstheappealingpotentialoftheAnammox-SAnMBRintreatinghigh-strengthnitrogenwastewaters.2014ElsevierB.V.Allrightsreserved.1.IntroductionHightotalnitrogen(TN)removal,energy-savingandsmallfoot-printarenotablefeaturesoftheanaerobicammoniumoxidation(Anammox)comparedtotheconventionalnitrification/denitrifica-tionsystem.InanAnammoxprocess,ammoniumisdirectlyoxi-dizedtonitrogengasunderanoxicconditionswithnitriteastheelectronacceptor[1].Hitherto,researchershademployedvariousofbioreactorstoachievehigh-rateofnitrogenremovalusingAnammoxbacteria,suchasgas-liftreactor,up-flowanaerobicsludgebed(UASB)reactorandup-flowfixed-bedbiofilmcolumnreactorswithnonwovenfabricsheet,etc.[2–5].However,acontin-uouslossofsmallAnammoxbiomassineffluentcouldresultinlowerobservedbiomassgrowthrate[6].Moreover,theseveresludgewashoutduetogranulefloatationcouldleadtoinstabilityorevensystemcollapses,especiallyathighloading.Therefore,itisessentialtokeepefficientretentionofbiomassforthestart-upandoperationofAnammoxprocess.Membranebioreactor(MBR)wasaneffectivefacilityforcultivatingslow-growingAnammoxbacteria.Itcouldkeepallthebacteriawithinthereactorratherthanbewashedawaywiththeeffluent.ResearchershadexploredthefeasibilityofcombiningAnammoxwithsubmergedanaerobicMBR(SAnMBR)[7–9].However,membranefoulingisthebottleneckoftheindustrial2014ElsevierB.V.Allrightsreserved.⇑Correspondingauthors.Tel.:+8641184706172(X.Xu).Tel.:+8641184706328(F.Yang).E-mailaddresses:xxcep@dlut.edu.cn(X.Xu),yangfl@dlut.edu.cn(F.Yang).ChemicalEngineeringJournal254(2014)9–16ContentslistsavailableatScienceDirectChemicalEngineeringJournaljournalhomepage:[10]reportedthatporeblockingattributedtothemaintypeofmem-branefouling.Moreover,particlesizeandsizedistributionplayanimportantroleinporeblocking,andsmallparticlescausemuchsevererfoulingthanthelargerones.Therefore,largeparticlesorsludgegranulationcouldreliefmembranefoulinginSAnMBR.SomepreviousstudiesreportedthatAnammoxbacteriacouldgrowinaggregatesorgranulesinMBRs[7,9].Arrojoetal.[11]reportedthattheAnammoxgranularsystemcouldbesuccessfullycarriedoutatacertainspecificinputpower.However,theinforma-tiononhowtoselectasuitablespecificinputpowertoimpeltheAnammoxflocsformgranulesinacontinuouslyfedandcom-pletelymixedMBRwasstilllimited.Anammoxbacteriahavehighactivitybutaslow-growingratewithadoublingtimeofweeks[6–8].Microbialgrowthandutiliza-tionofenvironmentalcontaminantsassubstrateshavebeenstud-iedbymanyresearchers[12,13].Ifsuitableenvironmentalandnutritionalconditionswereprovided,theslow-growingAnammoxbacteriamightexhibitexcellentsubstrateutilizationperformance,aswellasbenefitingbiomassgrowth.Nitritewastheelectronacceptor,butalsoapotentialinhibitorforAnammoxbacteria.Strousetal.[14]andsomeotherauthors[15,16]reportedaNO2-Nconcentrationshigherthan100mg/LcompletelyinhibitedtheAnammoxprocess.WhileLottietal.[17]reportedahigherinhibitionlevel(ahalfmaximalinhibitoryconcentrationof400mgNO2-N/L).Asaresult,investigatingtheNO2-Nbiodegrada-tionkineticsoftheAnammoxgranulesismeaningful,especiallyforAnammoxcultivatio