Aerationsystemdesigninintegratedfixedfilmac

Aerationsystemdesigninintegratedfixed-filmactivatedsludge(IFAS)andmovingbedbiofilmreactors(MBBR)usingstainlesssteelpipediffusers,manifold,anddownpipesChandlerJohnson1,JoshuaP.Boltz21ChiefTechnologyOfficer,WorldWaterWorks,Inc.,4000S.W.113thSt.,OklahomaCity,OK731732BiofilmTechnologiesPracticeLeader,CH2MHILL,Inc.,4350W.CypressSt.,Ste.600,Tampa,FL33605([e-mail])ABSTRACTAerobicintegratedfixed-filmactivatedsludge(IFAS)andmovingbedbiofilmreactors(MBBRs)useanengineeredaerationsystemconsistingofstainless-steelpipediffusers,manifold(orsubmergedairheader),downpipes,andmanuallyoperatedair-flowcontrolvalves.Theso-calledmedium-bubblediffuserhasalargediameter(i.e.,4-mm)orificethatissituatedalongtheundersideofthestainlesssteelpipediffuser.Therefore,medium-bubblediffusersarenotassusceptibletoscalingandfoulingasfine-bubblediffusers,andoperationalexperiencehasproventhatmedium-bubblediffusersrequiresignificantlylessmaintenancethanfine-bubblediffusers.Theoxygentransferefficiency(OTE)ofamedium-bubblediffuserisbetterthanthatofatypicalcoarse-bubblediffuser.ThepresenceoffreemovingplasticbiofilmcarriersinabioreactorimprovesOTE.Unfortunately,thereisnotagenerallyaccepteddesigncriteriafortheaerationsystemsthatareusedinaerobicIFASzonesandMBBRs.Thispaperwilldescribeamethodfordesigningastate-of-the-artaerationsystemforaerobicIFASzonesandMBBRs.Themethodologypresentedinthispapermaybeusedtodesignaerationsystemstypicalofstate-of-the-artaerobicfreemovingplasticbiofilmcarrier-basedreactors.KEYWORDS:integratedfixed-filmactivatedsludge;IFAS;movingbedbiofilmreactor;MBBR;mediumbubble;diffuser;aeration;aerobic;manifoldINTRODUCTIONState-of-the-artintegratedfixed-filmactivatedsludge(IFAS)andmovingbedbiofilmreactors(MBBRs)utilizefree-movingplasticbiofilmcarriers,wedgewireorperforatedplatecarrierretentionscreens,andasubmergedmixer(inananoxiczone)orstainless-steelpipediffusers,manifold(orsubmergedairheader),down(ordrop)pipes,andmanuallyoperatedair-flowcontrolvalves(inanaerobiczone).IFASrepresentsanevolutionoftheactivatedsludgeprocessthatallowshighervolumetricammonia-nitrogenconversionratesbycombiningbiofilmandsuspendedgrowthcompartments.Therefore,theestablishmentofgenerallyaccepteddesigncriteriaforIFASprocessandmechanicalfeaturesisimperativefortheapplicationofthisenvironmentalbiotechnology.However,thereispresentlyanimperfectunderstandingofIFASprocessandmechanicaldesignwhichhashinderedthewidespreadapplicationofthisenvironmentalbiotechnology.3781WEFTEC2013Copyright©2013WaterEnvironmentFederation.AllRightsReserved.Withoutinstitutionaldesigncriteria(andsupportingdesigntools)andknowledgeabouttheproperapplicationofIFASandMBBRs,theconsultingengineerwillrelyonmanufacturers(orvendors)todevelopandproposeaprocessandmechanicaldesign.ComparisonofamanufacturercontrivedIFASorMBBRprocessandmechanicaldesignwithprocessandmechanicaldesignsforalternativewastewatertreatmenttechnologiesthatweredesignedbyaconsultantwillnotallowforafaircomparisonbasedonequivalentstandardsdespitethefactthatbothdesignsweredevelopedforthesamewastewatertreatmentplant(WWTP)improvementorexpansionproject.Duetounknownsbybothparties,namelythemanufacturerandconsultant,itistypicalforconsultancydesignerstoincorporateconservatism(inthiscasetotheIFASprocessandmechanicaldesigns)thatcanresultinthetechnology(i.e.,IFAS)beingnon-competitivewithotheralternativesbeingevaluated(primarilyfromacostperspective).Thus,IFASmaybeinjudiciouslyeliminatedfromconsiderationalthoughthetechnologymaywarrantthemostsignificantmonetaryandoperationalbenefitshadthetechnologybeenproperlyevaluatedandcomparedwithcompetingenvironmentalbiotechnologies.Boltzetal.(2009a;2009b)andothershavecreatedprocessmodelsthataccuratelysimulateIFASandMBBRprocessperformance,andMcQuarrieetal.(2010)documentedpracticalIFASprocessdesignguidelines.Boltzetal.(2010a)andMcQuarrieandBoltz(2011)have(1)presenteddesigncriteriaforsizingfree-movingplasticbiofilmcarrierretentionscreens,(2)establishedpracticallimitationsfortheamountoffree-movingplasticbiofilmcarriersthatmaybeplacedinabioreactor,and(3)definedsystemhydraulicswiththresholdparametersincludingthebasinapproachvelocityandcarrierretentionscreenhydraulicloadingrate.Therefore,processmodel(s),free-movingplasticbiofilmcarrierretentionscreensizingcriteria,IFASzoneorMBBRbasinconfigurationstandards,andcriteriadescribingtheamountoffree-movingplasticbiofilmcarriers(orbiofilmsurfacearea)thatarerequiredtomeetawastewatertreatmentobjectiveexist,havebeendocumentedandreferencedinthismanuscript,andhavebeendemonstratedaccurateinmultiplefull-scale,operatingaerobicIFASzonesandMBBRs(includingsecondaryprocesses,post-denitrification,andtertiarynitrification).However,thedescriptionofacomprehensivemethodologyforstate-of-the-artaerobicIFASzoneandMBBRaerationsystemdesign,totheknowledgeoftheauthors,hasnotbeenpresented.Inthispaper,theaerationsystemincludesstainless-steelpipediffusers,manifold(orsubmergedairheader),down(ordrop)pipes,andmanuallyoperatedair-flowcontrolvalves.Thismanuscriptwillpresentamethodforthedesignofanaerationsystemi