Evaluatingtheeffectofbiofilmthicknessonnitr

FullTerms&Conditionsofaccessandusecanbefoundat=tent20EnvironmentalTechnologyISSN:0959-3330(Print)1479-487X(Online)Journalhomepage:önsson&ThomasWelanderTocitethisarticle:MariaPiculell,PiaWelander,KarinJönsson&ThomasWelander(2016)Evaluatingtheeffectofbiofilmthicknessonnitrificationinmovingbedbiofilmreactors,EnvironmentalTechnology,37:6,732-743,DOI:10.1080/09593330.2015.1080308Tolinktothisarticle::21Aug2015.Publishedonline:06Oct2015.SubmityourarticletothisjournalArticleviews:361ViewrelatedarticlesViewCrossmarkdataCitingarticles:3ViewcitingarticlesEvaluatingtheeffectofbiofilmthicknessonnitrificationinmovingbedbiofilmreactorsMariaPiculella,PiaWelandera,KarinJönssonbandThomasWelanderaaAnoxKaldnesAB,Klosterängsvägen11A,SE-22647,Lund,Sweden;bWaterandEnvironmentalEngineeringattheDepartmentofChemicalEngineering,LundUniversity,P.O.Box124,SE-22100,Lund,SwedenABSTRACTThisstudyevaluatestheeffectofbiofilmthicknessonthenitrifyingactivityinmovingbedbiofilmreactors(MBBRs)inacontrolledenvironment.In-depthunderstandingofbiofilmpropertiesinMBBRsandtheireffectontheoveralltreatmentefficiencyisthekeytooptimizingprocessstabilityandefficiency.However,evaluatingbiofilmpropertiesincontinuouslyoperatedMBBRscanbeextremelychallenging.Thisstudyusesacarrierdesignwhichenablescomparisonoffourdifferentbiofilmthicknesses,inotherwiseequallyoperatedlab-scaleMBBRs.Theresultsshowthatwithinthestudiedrange(200–500µm)andspecificoperationconditions,biofilmthicknessalonehadnosignificanteffectontheoverallammoniumremoval.Thenitrateproduction,however,decreasedwithadecreasingbiofilmthickness,andtheratiobetweennitriteandammonia-oxidizingactivitydecreasedbothwithincreasingloadanddecreasingoxygenconcentrationforallthicknesses.Thesuggestionthatnitratationisdisfavouredinthinbiofilmsisaninterestingcontributiontothecurrentresearchbeingperformedonnitrite-oxidizingbacteriainhibitionfordeammonificationapplications.Byindicatingthatdifferentgroupsofbacteriaresponddifferentlytobiofilmthickness,thisstudyaccentuatestheimportanceoffurtherevaluationofthesecomplexsystems.ARTICLEHISTORYReceived8April2015Revised29July2015Accepted29July2015KEYWORDSBiofilmthickness;biologicalnitrogenremoval;nitrification;movingbed;oxygenlimitationIntroductionBiofilmprocessesplayanimportantroleinbiologicalwastewatertreatment,wherethelongsludgeagesinthebiofilmfacilitateslowmicrobialprocesses.Oneincreasinglypopularbiofilmprocessisthemovingbedbiofilmreactor(MBBR),wherethebiofilmgrowsonasus-pendedcarriermaterialinordertopreventcloggingandtoincreasetreatmentefficiency.IntheconventionalMBBR,thebiofilmmostlygrowsontheprotectedsur-facesinsidethecarriers,withoutbeingexposedtoexter-nalabrasion,andtheremovalrateofnutrientsishencequantifiedastheremovalperprotectedsurfacearea(PSA)ofcarrierused.[1]TheMBBRisparticularlyadvantageousforslowpro-cessessuchasnitrification,definedasthebiologicalprocesswhereammoniaisoxidizedtonitratebyauto-trophicbacteria.Duetotheslowgrowthofautotrophicbiomass,nitrificationisoftenthemostcriticalstepinbio-logicalnitrogenremoval.Althoughnitrificationisusuallyconsideredasaone-stepprocessinwastewaterengineer-ing,itisknowntoconsistoftwosteps.Thesetwostepsinvolve(1)ammonia-oxidizingbacteria(AOB)convertingammoniatonitrite,followedby(2)nitrite-oxidizingbac-teria(NOB)convertingnitritetonitrate.Undernormalconditionsthefirststepisratelimiting,andnitriterarelybuildsupinthewastewatertreatmentprocess.However,atelevatedtemperatures(above20°C),theoxi-dationrateofammoniaexceedstheoxidationrateofnitrite,[2,3]andnitritemayaccumulateinthesystem.InMBBRs,thenitrifyingactivitydependsstronglyontheoxygenavailability,andiscommonlyobservedasafirst-orderfunctionofthebulkliquidoxygenconcen-tration.[4–7]Thediffusionofoxygen(andothercom-pounds)fromthebulkliquidintothebiofilmisthemajorrate-limitingprocessinMBBRs[8]andtheresultingconcentrationgradientsinsidethebiofilmwilldeterminethebiofilmcomposition.[9]Generally,biofilmsinaerobicMBBRsareonlypartiallypenetratedbyoxygen.Depend-ingonbulkliquidoxygenconcentration,hydro-dynamicsandbiofilmdensity,theoxygenpenetrationdepthinbio-films(fromdifferentwastewatertreatmentsystems)canvarybetween50and500µm.[9–13]Whenthebiofilmthicknessexceedstheoxygenpenetrationdepth,thereisalayerofanoxicand,sometimes,anaerobicbiomassunderneaththeaerobicallyactivebiofilm.Asdiffusionlimitationsresultinrestrictedpenetrationofsubstrates,ithasbeensuggestedthattheidealbiofilminMBBRsisthinandevenlydistributedoverthecarriersurface.[1,14]©2015Taylor&[e-mail]GY,2016VOL.37,NO.6,732–743films,thenitrificationefficiencyinconventionalMBBRsmaywelldependonthebiofilmthickness,asanincreasedbiofilmthicknessinsidethevoidsofth