StartupofPostDenitrificationMBBRPilottoAchi

StartupofPostDenitrificationMBBRPilottoAchieveLimitofTechnologyatBluePlainsAWTPMarijaPeric1*,DilliNeupane1,BeverleyStinson1,EdwardLocke1,KathleenKharkar1,SudhirMurthy2,WalterBailey2,SalilKharkar2,NicholasPassarelli2,JohnCarr2,RoubenDerMinassian2,George(Yi-Ming)Shih21Metcalf&Eddy,14504GreenviewDrive,Suite400,Laurel,MD,207082DCWASA,5000OverlookAvenueSW,WashingtonDC,20032*Email:[e-mail]enitrification,MBBR,LimitofTechnology,ENRINTRODUCTIONTheDistrictofColumbiaWaterandSewerAuthority(DCWASA)isinvestigatingcost-effectiveandreliableprocessalternativestomeetalimitoftechnology(LOT)totalnitrogen(TN)andtotalphosphorus(TP)effluentrequirements.OneofthealternativeprocessapproachesunderconsiderationincorporatesaninnovativeMovingBedBiofilmReactor(MBBR)technologyasadenitrificationpolishingstepdownstreamoftheexistingnitrification/denitrificationactivatedsludgesystem.DCWASAcurrentlyoperatesitswastewatertreatmenttomeetaTNeffluentlimitof7.5mg/L.Anewpermithasbeenissuedthatwillrequireadditionaldenitrification.TounderstandtheapplicabilityofMBBRtechnologyattheBluePlainsAdvancedWastewaterTreatmentPlant(AWTP)anditsabilitytoreliablyandcosteffectivelyassistinmeetingtheeffluentTNrequirements,apilotfacilitywasimplementedandhadbeeninoperationbetweenlateOctober2007andearlyJuly2008.Auniqueaspectofthediscussionaddressesthecyclicalaerobic/anoxicmethodologyusedtoacceleratemethylotrophicgrowthandsystemstartupaswellasperformanceundertheambienttemperatureofapproximately17°C.GOALSANDOBJECTIVESTheoverallgoalofthispilotstudywastodetermineiftheMBBRprocesscanreliablyandcost-effectivelymeettheeffluentENRgoalsoverarangeofoperatingconditionswithoutimpactingthecurrentplantoperations.The“proofofconcept”testplanwasconductedinthreephaseswhichwouldaddressthekeyaspectssuchasthedenitrificationperformanceandreliability(thatwasdefinedbytheabilitytofullydenitrifytoeffluentNOx-Nlevelsof0.5to1mg/Lwithinanoxichydraulicdetentiontimesofabout30minutesatambientandlowtemperatures),performanceresponsetostressconditions(higherflowsandnitrateloads),andphosphorusdemandandimpactsofphosphoruslimitations.Thispaperpresentsstartupandambienttemperaturedenitrificationperformance.Coldtemperature(12°C),NOx-Nloadstressandphosphoruslimitationperformancewillfollow-upinthesubsequentpapers.WEFTEC®.08Copyright©2008WaterEnvironmentFederation.AllRightsReserved.308METHODOLOGYThepostdenitrificationMBBRpilotprocessattheBluePlainsAWTPconsistedoftwoindependenttrains,eachconsistedoftwo100-gallonanoxictanksandone150-gallonpostaerationtank.Atthetimeofstresstesting,oneofthetrainswasusedasacontroltrain.Bothanoxicandpost-aerationtankswerefilledwith30%ofmedia.IDIActiveCell515@mediawithspecificsurfaceareaof515m2/m3wasbeingusedinthispilotstudy.TotalanoxicHRTwas30min.RESULTSANDDISCUSSIONMBBRmediawasinitiallyacclimatedfor6weeksinabatchtankwithnitrifiedeffluentfromtheactivatedsludgesystemasinfluentfeed,andmethanolandphosphorusbeingaddedonceaday.Acclimatedmediawasthentransferredintothepilotreactors.DuringtheearlystartupperiodtheDOwasoccasionallyelevatedtolevelsashighas3.3mg/LintheMBBRanoxictankstoencouragetherapidaerobicgrowthofthemethanoldegraders.Growthofthebiomasswasmonitoredusingin-situbatchtestsasbiofilmgrowthwasdifficulttoobservevisually.Allfouranoxictankswerespikedwithhighnitrate,andexcessofmethanolandphosphorus.Thereactorsdemonstratedrapidstartupandnitratereductionratesintheorderof0.72to2g/m2/dwithinaneightweekperiod(October–December2007).Itappearsthatthestrategyofthecyclicalaerobic/anoxicmethodologycoupledwithin-situbatchtesthasencouragedtherapidmethylotrophicgrowthonthemedia.ThefirstphaseofthepilotingstartedinmidDecember2007untiltheendofMarch2008.ThesummaryoftheMBBRperformanceispresentedinTable1.Train1wasoperatedatthedesignmaximummonthloadingrateof1.6g/m2/d.LessconservativeloadingratewasappliedtoTrain2tounderstandtheimpactofloadingraterangesonthepilotperformances.Table1.MBBRPilotPerformanceSummaryunderambienttemperatureof16.6°CTrain1Train2LoadingrateofNOx-N,g/m2/d1.61.3InfluentNOx-Nconcentration,mg/L5.14.1RemovalrateofNOx-N,g/m2/d1.41.1EffluentNOx-Nconcentration,mg/L0.60.5EffluentbsCOD,mg/L10.310.7gsCODconsumed/gNOx-Nremoved4.34.5gPO4-Pconsumed/gTSSproduced(%)1.8%2.3%gTSSproduced/gNOx-Nremoved1.81.5OverallpercentofNOx-Nremovalinbothtrainswas88%.Itisimportanttonotethatthisphasewasoperatedwithexcesscarbon(methanol)andphosphorus.Targetedexcesscarbonwas10-15mg/LofbiodegradablesolubleCOD(bsCOD)intheeffluentfromthesecondanoxicreactors.Excessphosphoruswas0.3–0.4mg/LasPO4-Pintheeffluentfromthesecondanoxicreactor.CONCLUSIONSMBBRpostdenitrificationprocesswascapableofachievingeffluentNOx-Nofabout0.5mg/Londesignmaximummonthloadingratesof1.6g/m2/dundertheambienttemperatureWEFTEC®.08Copyright©2008WaterEnvironmentFederation.AllRightsReserved.309of17°C.ThisisanimportantfindingtounderstandtheperformanceoftheMBBRonannualaveragebasis.However,thecriticalperformanceoftheMBBRstillneedstobeevaluatedunderthecoldtemperature(designof12°CfortheBluePlainsAWTP)underthemaximummonthlyloadandph