2011ESTSegregationofBiomassinCyclicAnaerobicAerobi

Published:July08,2011r2011AmericanChemicalSociety7330dx.doi.org/10.1021/es201388t|Environ.Sci.Technol.2011,45,7330–7337ARTICLEpubs.acs.org/estSegregationofBiomassinCyclicAnaerobic/AerobicGranularSludgeAllowstheEnrichmentofAnaerobicAmmoniumOxidizingBacteriaatLowTemperaturesMariK.H.Winkler,†RobbertKleerebezem,†J.GijsKuenen,†JingjingYang,†,‡andMarkC.M.vanLoosdrecht*,††DepartmentofBiotechnology,DelftUniversityofTechnology,Julianalaan67,2628BCDelft,TheNetherlandsbSSupportingInformation’INTRODUCTIONTheprocessofAnammoxisashortcutinthenitrogencyclewherebyammoniumisoxidizedwithnitritetonitrogengas.1FortheapplicationofAnammoxforammoniumremovalfromwastewater,itisrequiredtoproducenitritebyammoniumoxidizingbacteria(AOB)andcombineitwiththeanaerobicoxidationofammoniumattheexpenseofthenitriteproduced.SinceitsdiscoverybyMulderin19922manyAnammoxbasedtreatmentsystemshavesuccessfullybeenimplementedforcost-efficientfull-scalenitrogenremovalfromanaerobicsludgediges-tionrejectionwater.3
5ToestablishgoodnitrogenremovalAnammoxandAOBneedtobeenrichedinthereactorsystem,whilenitriteoxidizingbacteria(NOB)needtobeoutcompeted.Differentstrategieshavebeendevelopedtocontrolthiscompeti-tion,andasuiteofprocessesisappliedatfullscalefornitrogenremovalfromwastewaterwithrelativehighammoniumcontentandhighertemperatures(20
C).6Inasinglereactorforhighactivityammoniumremovalovernitrite(Sharon)systemthepreferentialproductionofnitriteinsteadofnitratefromammoniumisaccomplishedbyexploitingthehighergrowthrateofAOBcomparedtoNOBathigheroperationaltemperatures.ThisallowsforselectionofAOBandwash-outofNOBsimplybyreducingthesolidretentiontimetoapproximatelyoneday.7InthesubsequentAnammoxreactorAOBandNOBcannotgrowduetoabsenceofoxygen.InprocesseswhichcombinenitritationandAnammoxinonereactor,alsothehighergrowthrateofAOB(ascomparedtoNOB)contributestopreventingnitrateformationbyNOB.CurrentresearchstudyingtheeffectoflowtemperaturesonAnammoxactivityisshowingthatAnammoxcancopewithlowertemperatures.8
10However,forapplicationofaone-stageNitritation/Anammoxprocessatlowertemperatures,likethoseencounteredinsewage,itisnecessarytogainmoreinsightinthemicrobialcompetitionbetweenAOB,NOB,andAnammox.InaonestagesystemthecompetitionbetweenAnammoxandNOBfornitriteandbetweenAOBandNOBforoxygenisthemajorissueinselectingthedesiredpopulation.Lowoxygenconcentra-tionshavebeenproposedtofavorAOBinpreferencetoNOBfortheirelectronacceptoroxygen.11Inoxygenlimitedone-stageAnammoxsystems,all3groupsofbacteriadonotgrowinsuspensionbutareagglomeratedinonecompactgranule.Theminimumsludgeretentiontime(SRT)requiredisthereforedefinedbytheslowgrowingAnammoxbacteria,makingitimpossibletoselectagainstNOBbasedongrowthrate.Received:April22,2011Accepted:July8,2011Revised:June20,2011ABSTRACT:Acyclicanaerobic/aerobicbubblecolumnreactorwasrunfor420daystostudythecompetitionfornitritebetweennitriteoxidizingbacteria(NOB)andanaerobicammoniumoxidizingbacteria(Anammox)atlowtemperatures.Ananaerobicfeedingperiodwithnitriteandammoniumintheinfluentfollowedbyanaeratedperiodwasappliedresultinginabiomassspecificconversionrateof0.18(0.02[gN2
N3gVSS
13day
1]whenthedissolvedoxygenconcentrationwasmaintainedat1.0mgO23L
1.Anincreaseinwhitegranuleswasobservedinthereactorwhichweremainlylocatedatthetopofthesettledsludgebed,whereasredgranuleswerelocatedatthebottom.FISH,activitytests,andqPCRtechniquesrevealedthatredbiomasswasdominatedbyAnammoxbacteriaandwhitegranulesbyNOB.Granulesfromthetopofthesludgebedweresmallerandthereforehadahigheraerobicvolumefraction,alowerdensity,andconsequentlyaslowersettlingrate.SludgewasmanuallyremovedfromthetopofthesettledsludgebedtoselectivelyremoveNOBwhichresultedinanincreasedoverallbiomassspecificN-conversionrateof0.32(0.02[gN2
N3gVSS
13day
1].BiomasssegregationingranularsludgereactorsgivesanextraopportunitytoselectforspecificmicrobialgroupsbyapplyingadifferentSRTfordifferentmicrobialgroups.7331dx.doi.org/10.1021/es201388t|Environ.Sci.Technol.2011,45,7330–7337EnvironmentalScience&TechnologyARTICLERecentlywedemonstratedthatinaerobicgranularsludgeverticalsegregationofgranulesoccursbasedonsmalldifferencesinsettlingvelocityofthegranules.12Granuleswithahigherdensityanddiameteraccumulateatthebottomofthesludgeblanket.Sincebiomassinthebottomandthetopofthesludgebedareexposedtodifferentsubstrateconcentrationsduringfeeding,differentmicrobialcommunitiesmaydevelopasafunctionofheightinthesludgebed.Selectivesludgewithdrawalfromeithertoporbottomofthesludgebedcanthereforebeusedasapossibilitytocontrolthemicrobialcommunitystructureinagranularsludgereactor.Interestingly,mathematicalmodelshaverecentlyindicatedthatmicrobialpopulationsingranulescanbeinfluencedbyparticlesizedistribution.Foranitritation/anammoxgranularsludgeprocessitwasdemonstratedthatNOBsarefavoredtogrowinsmallergranulessupposedlybecauseofthehigherfractionalaerobicvolumefornitrification.13BiggergranuleshaveasmalleraerobicvolumefractionwhichisinadvantageofAnammox.14Anammoxcanaccumulatetolargeramountsintheselargegranulesandthereforemaintainalownitriteconcentrationinsidethegranuleleadin