MBBRandIFASPilotProgramforDenitrificationat

WaterPractice™•Vol.1•No.5©2007WaterEnvironmentFederation•doi:10.2175/193317707X256955MBBRandIFASPilotProgramforDenitrificationatFairfaxCounty’sNomanColePollutionControlPlantSarahMotsch1,DanFetherolf1,GeorgeGuhse2,JohnMcGettigan3,TomWilson3*1FairfaxCounty,NomanM.ColePollutionControlPlant,9399RichmondHighway,Lorton,VA220792GreeleyandHansen,6551LoisdaleCourt,Suite603,Springfield,VA,221503EarthTech,675N.WashingtonStreet,Suite300,Alexandria,VA22314,*Towhomcorrespondenceshouldbeaddressed.Email:[e-mail]treductionprogram,developedtomeetnewVirginiaENRrequirements,twoinnovativedenitrificationtechnologieswerepilotedattheNomanColeJr.WaterPollutionControlPlantinFairfaxCounty,Virginia.ThefirsttechnologywasaMovingBedBiofilmReactor(MBBR).ThesecondtechnologywasamodifiedIntegratedFixedFilmActivatedSludge(IFAS)process.Thesestudieshaveshownthatbothtechnologiescanbeusedfordenitrificationattheplant.EachwasshowntobeeasilycapableofreducingthepilotinfluentNOx-Nof7mg/Ltobelow2mg/LNOx-Nattheloadingsstudied.TheMBBRsystemwasshowntobesensitivetoinfluentortho-phosphatelevelsbelow1.0mg//l.Onlyabout1.25gmofexcessTSSwasproducedpergmofNOx-Nremoved,intheMBBRsystem.KEYWORDS:Denitrification,MBBR,LimitofTechnology(LOT),IFAS,ENR.INTRODUCTIONFairfaxCountyrecentlydevelopedaNutrientReductionProgram(NRP)fortheNomanColePollutionControlPlant(NCPCP)toprovidefortheprotectionandrestorationoftheChesapeakeBaythroughthefurthercontrolofnitrogenandphosphorousattheplant.TheNRPwillallowthefacilitytomeetVirginia’snewEnhancedNutrientRemoval(ENR)regulationsrequiringverylowlevelsoftotalnitrogendischarge.Aspartoftheprogram,twoinnovativedenitrificationtechnologieswerepilotedattheNCPCPinordertodeterminethesite-specificlimitoftechnologyintermsofnitrogenremoval.ThefirsttechnologywasaMovingBedBiofilmReactor(MBBR).ThesecondtechnologywasamodifiedIntegratedFixedFilmActivatedSludge(IFAS)process.MBBRandIFASprocesseshaveonlyrecentlybeenappliedtonitrificationapplicationsinNorthAmerica.InEurope,MBBRshavebeenappliedtobothnitrificationanddenitrification.MostoftheEuropeandenitrificationapplicationsaredesignedtotakehighlevelsofnitratetomoderatelevelsofnitrate.Atthetimeofthestudy,onlyoneplantwasknowntobeachievingeffluentNitrate-Nlevelssimilartowhatwasneeded.Thisplant,inSjölundaSweden,wasachieving1.7mg/LNitrate-N,butstartingathigherconcentrations(15.6mg/Lnitrate-N),usingmuchlongerdetentiontimes(70minutes)andoperatingatmuchlowerloadings(1.05gN/m2/d)thanstudiedherein(EarthTech,2005).SubsequenttothestudiestheauthorsbecameawareofplantinCabooltureAustralia,designedatsimilarloadings,butusing40%mediafillandoperatinginwarmerwater(20-26°C)whichhasbeenproducingeffluentscontaininglessthan1.0mg/lLnitrate-N(averaging0.84mg/Lrecently)sinceabout2000(McSweeny,2007).InFairfaxCounty,theprocessneedsweretostartfromamoderatenitratelevelofabout7mg/landreliablytakethenitrogentoverylowlevelsattemperaturesaslowas13°C.Thisnewapplicationoftheseprocessesincludedassessingtheeffectivenessofmultiplestagesandanassessmentofthepracticalremovallimitsofthesetechnologies.Thetwomajorobjectivesforthispilotstudywereto:Motschetal.WaterPractice™•Vol.1•No.5©2007WaterEnvironmentFederation•doi:10.2175/193317707X2569552(1)ConfirmtheabilitytoreliablymeetaTotalNitrogen(TN)effluentlimitof3.0mg/LrequiringtheeffluentNOx-N(Nitrate-N+Nitrite-N)tobebelow2mg/L.(2)DeterminehowlowNOx-Ncouldbeachievedbyusingmultiplestagesofeachprocess.ThestudywasconductedbetweenFebruary2006andApril2006.Thispaperwilldiscussthefindingsofthesetwopilotstudies.METHODOLOGYThelayoutofboththeMBBRpilotandtheLastPassIFASpilotisshowninFigure1.Thetwopilotsystemswereoperatedindependentlyofeachother.Whileasinglechemicalstoragetankforeachchemicalwasusedforbothoftheseunits,individualpumpswereprovidedforchemicalmeteringforeachpilotunit.Figure1—PilotLayout.Bothoftheunitswereoperatedinadiurnalflowpattern,byincreasingtheflowto130%ofthedesignflowfrom10:00AMto4:00PM.Unfortunately,fromApril12thtoApril16th,flowtoIFASpilotcouldnotbevariedtomimicthediurnalflowpatternduetoinstabilityofthepump.Aconstantflowof130%ofdesignflowwasappliedforthatperiod.MBBRMBBRsoperatebyallowingnitrifiedsecondaryeffluenttopassthroughatankofmedia.Theprocessisapurebiofilmprocesswithoutsludgerecirculation.Thedenitrifyingbacteriaattachtothemedia,whichisavailableinavarietyofmaterials,shapes,andsizes.TheMBBRpilotconsistedofasmallday-tank(forflowcontrol)andthree160-gallonreactortanks.InfluenttotheMBBRwaspumpedfromthecommonsecondaryeffluentchannelneartheendofsecondaryclarifier#15.ApartialsiteplanisshowninFigure2.Aconstantratepumpfedtheday-tanklocatedinthetrailer.Avariablespeedpumpsentflowfromtheday-tanktotheMBBRtankR-1.Thispumpallowedthevariationoftheinflowtosimulateadiurnalflowpatternintheplant.Methanolwasaddedasanexternalcarbonsourceandintentionallyoverdosedtomaintainatleast5partsmethanolperpartofnitrate-N.Calculateddoseswereatapproximately40mg/Lduringmostofstudy,includingtheApril6throughendofstudy.Mechanicalproblemsresultedinunderdosingduringpartofstudy.AnitratesolutionMBB