EvaluationofPlasticCarrierMediaImpactonOxyg

EvaluationofPlasticCarrierMediaImpactonOxygenTransferEfficiencywithCoarseandFineBubbleDiffusersHaoPham1*,SudhakarViswanathan1,RobertF.Kelly21DegremontTechnologies–Infilco,Richmond,VA,USA.2DegremontNorthAmericanResearchandDevelopmentCenter,Richmond,VA,USA.*Towhomcorrespondenceshouldbeaddressed.Email:[e-mail]uctedusingan840gallontesttanktoevaluatetheimpactofcarriermediaonstandardoxygentransferefficiencyincleanwater(SOTEcw),usingcoarseandfinebubbleairdiffusersusedinIntegratedFixed-FilmActivatedSludgeandMixedBedBiofilmReactorsystems.TheobjectivesofthisstudyweretoevaluatetheimpactofvariousfillvolumesofcarriermediaonSOTEcw,tobetterunderstandthemovementofthecarriermediaatdifferentfillfractionswiththeuseofdifferentdiffusertypesandtodeterminetheminimumairflowrequiredtoachievemediarollatdifferentfillfractions.Resultsshowthatwithupto50percentmediafill,thefinebubblediffuserSOTEcwisabouttwicethatofthecoarsebubble.TheresultsconfirmthatthemostsignificantfactorimpactingSOTEcwisthediffusertype,withfinebubblediffusersyieldingsignificantlyhigherefficienciesascomparedtocoarsebubblediffusers.KEYWORDS:standardoxygentransferefficiency,IntegratedFixed-FilmActivatedSludge,MixedBedBiofilmReactor,offgas,diffuserINTRODUCTIONAlthoughmanystudieshavebeenperformedoncleanwateroxygenstandardtransferefficiency(SOTEcw)withinActivatedSludgesystemsusingdifferenttypesofairdiffusers,littleinformationisavailablewithrespecttotheimpactofthecarriermediaonOTEwithinIFAS/MBBRsystems.TheprimaryobjectiveofthisstudyistoevaluatetheimpactofvariousfillvolumesofcarriermediaonthecleanwaterOTE,usingtwopre-selecteddiffusertypes,onecoarsebubbleandonefinebubble.Thesecondaryobjectivesofthetestingwere:•Tobetterunderstandthemovementofthecarriermediaatdifferentfillfractionswiththeuseofdifferentdiffusertypes.•Todeterminetheminimumairflowrequiredtoachievemediarollatdifferentfillfractions.WEFTEC®.08Copyright©2008WaterEnvironmentFederation.AllRightsReserved.5069Thisstudy,thefirstoftwo,servedasaprecursortothefuturestudy,whichwillbeperformedatalargerscalewithanemphasisonoptimizingdiffuserlayouts.METHODOLOGYEquipmentDescriptionTheOTEtestingwasconductedinan840gallonsteeltesttankhavingdimensions4’x4’x7’(LxWxH)asshowninFigure1.Alltestswereconductedataworkingwaterdepthof6.5feet,hencetheresultsobtainedarereflectiveofthiscondition.Figure1.OffGasAnalysisTestTankWEFTEC®.08Copyright©2008WaterEnvironmentFederation.AllRightsReserved.507016.751112251511.5FineBubbleDiffusersCoarseBubbleDiffuser4848Figure2.TestTankGridLayoutShowingDiffuserPositionsFigure3.DiffuserMountingAssemblyWEFTEC®.08Copyright©2008WaterEnvironmentFederation.AllRightsReserved.5071TestSetupandMethodologyA9”finebubblediffuseranda24”coarsebubblediffuserwerechosenastherepresentativediffusersforusewiththeOTEtesting.Thediffuserswerearrangedinapartialgridpatternononesideofthetanktocreateasinglerollpattern.AcommondiffusermountingassemblyallowedforinstallationofonecoarsebubblediffuserononesideofthetesttankandthreefinebubblediscsontheoppositesideofthetankasillustratedinFigure2.Thisarrangementallowedforallteststobeconductedwithoutremovalofthecarriermediabetweentestruns.Thecoarsebubblediffuserwaspositioned0.5feetfromthebottomofthetankwhereasthefinebubblediffuserswerepositioned1.0footfromthebottomofthetank.Alltestingwasconductedwiththesametypeofcarriermedia.Thenewcarriermediawassoakedforoversevendayspriortoconductingthestudyinordertoremoveanychargethatmightcreateabuoyancyeffectandthusnegativelyaffectmixing.Theconditionstestedincludedmediafillratiosof25and50percentandacontrolwithnocarriermedia,notingthatallwereevaluatedusingthesamediffuserlayout.Alltestsconductedwiththecarriermediawereperformedundertherequiredconditionsofestablishingarollpattern.Foreachdiffusertype,threeairflowratesweretestedforeachofthecarriermediafillfractionsevaluated.Theminimumairflowratenecessarytomaintainadequatemixinginthetesttank,definedbywayofestablishingamediarollpattern,wasdeterminedforeachdiffuseratallfillfractionstested.Thehighestairflowratestestedwerechosenbasedontheexpectedfluxforeachdiffusertypeunderfull-scaledesignconditionsasrecommendedindustrystandards.Foralltests,residualdissolvedoxygenwasmaintainedat2-4mg/Lwiththeadditionofammoniumsulfateasanoxygenscavenger.SamplingOffgasmeasurementandanalysiswereconductedusinganEwingEngineeringMarkVAeratorRatorOffGasAnalyzer(Figure4),employingcarbondioxideandwatervaporstrippingtomeasureoxygencontentfordeterminationofsystemOTE.Ahoodcoveringtheentiretesttankwasusedtocollecttheexitinggas,whichisthendrawnbywetvacuumthrougha2”hosetotheoffgasanalyzer.Thegasisrunthroughacolumnpackedwithsodiumhydroxide(supportedwithinPVCpellets)andDrierite®desiccanttoremovecarbondioxideandhumidity,respectively.Theanalyzersimultaneouslydrawsinthegasfromthehoodandambientair.ADissolvedOxygen(D.O.)meterintheanalyzerisabletomeasureoxygenconcentrationsofeitherofthetwogasstreams.Theoffgasanalyzermeasuresthepartialpressureofoxygenindried,ambientairandcomparesittothatoftheoffgasexitingthesurfaceoftheaer