AnInvestigationofMovingBedBiofilmReactorNit

AnInvestigationofMovingBedBiofilmReactorNitrificationduringLong-TermExposuretoColdTemperaturesValerieHoang1,RobertDelatolla1*,EdithLaflamme2,AlainGadbois2ABSTRACT:Biologicaltreatmentisthemostcommonandeconomicalmeansofammoniaremovalinwastewater;however,nitrificationratescanbecomecompletelyimpededatcoldtemperatures.Attachedgrowthprocessesand,specifically,movingbedbiofilmreactors(MBBRs)haveshownpromisewithrespecttolow-temperaturenitrification.Inthisstudy,twolaboratoryMBBRswereusedtoinvestigateMBBRnitrificationratesat20,5,and18C.Furthermore,thesolidsdetachedbytheMBBRreactorswereinvestigatedandArrheniustemperaturecorrectionmodelsusedtopredictnitrificationratesafterlong-termlow-temperatureexposurewasevaluated.Thenitrificationrateat58Cwas6663.9%and6463.7%comparedtotheratemeasuredat208Cforreactors1and2,respectively.Thenitrificationratesat18Covera4-monthexposureperiodcomparedtotherateat208Cwere18.765.5%and15.764.7%forthetworeactors.ThequantityofsolidsdetachedfromtheMBBRbiocarrierswaslowandthemassofbiofilmpercarrierdidnotvarysignificantlyat208Ccomparedtothatafterlong-termexposureat18C.Lastly,atemperaturecorrectionmodelbasedonexposuretimetocoldtemperaturesshowedastrongcorrelationtothecalculatedammoniaremovalratesrelativeto208Cfollowingagradualacclimatizationperiodtocoldtemperatures.WaterEnviron.Res.,86,36(2014).KEYWORDS:biofilm,movingbedbiofilmreactor,ammoniaremoval,nitrification,coldtemperatures,wastewater.doi:10.2175/106143013X13807328848694IntroductionAmmoniaisadeleteriousconstituentreleasedfromwaterresourcerecoveryfacilities(WRRFs)andisresponsibleforacuteandchronictoxicitiesinlakesandriverswheretreatmentisnotapplied(Chambersetal.,1997).Ammoniaremovalinconven-tionalnorthernWRRFsiscurrentlyatriskofbeinglimitedornonexistentinwintermonthsbecauseofseverelycoldtemperatures.Therefore,ammoniadischargeinwastewatereffluenthasrecentlybeenregulatedbynortherncountries,suchasCanada,toreducerisktofisheriesresources,ecosystemhealth,andhumanhealth(CanadaGazette,2012).Numerousstudiesandpracticalexperiencehaveidentifiedtheeffectoflowtemperaturesonnitrifyingbacteriaasthecauseforlossofnitrification(SharmaandAhlert,1977;PainterandLoveless,1983;Salvettietal.,2006;ZhuandChen,2002).Attachedgrowthprocessesand,specifically,themovingbedbiofilmreactor(MBBR)haveshownpromiseinachievingshort-termammoniaremovalatcoldtemperaturesbelow48C(Andreottolaetal.,2000;Delatollaetal.,2011;WessmanandJohnson,2006).Movingbedbiofilmreactortechnologieshavebecomeanattractiveprocesscomparedtoconventionaltreatmentprocess-es.Movingbedbiofilmreactorsarecompactunitsthatusethewholetankvolumeandoffertheadvantageofeasysolidsseparation,nosludgerecycling,andnobackwashing(Ødegaard,2006).TheMBBRprocessusesbiocarriers,whichvaryinsizeandshape,tosupportandmaintainthegrowthofactivebiofilmwithinthetreatmentsystems.Anaerationsystemisincorpo-ratedtothesystemtokeepthecarriersinconstantsuspensionandmovementtoprovidetheattachedbiofilmwithadequateoxygenandaccesstothebulkliquidsubstrate.Theactivebiofilmgrowsontheinnerportionofthecarrierwhereitisprotected,toacertaindegree,fromexternalcollisionsandforces.TheoperatingandmaintenancecostsassociatedwithMBBRtechnologiesaregenerallylowandarecapableofproducinganeffluentwithatotalammonia-nitrogenconcen-trationlowerthan5mg/Latarangeofflowratesandunderconventionaltreatmenttemperatures(EnvironmentCanada,2003).Withmorethan1,000treatmentlagoonsinoperation,thistreatmentsystemrepresentsthemajorityofwastewatertreatmentfacilitiescurrentlyoperatinginCanada(EnvironmentCanada,2003).TheperformanceofnitrifyingMBBRupgradesystemsinnortherncountrieshasbeendemonstratedataselectionofoperatinglagoonswiththeMBBRunitbeinginstalledtotreatwastewaterexitingfromthefirstpondofmultipletreatmentlagoonponds,wherethetemperaturedropislimited(Delatollaetal.,2011;Houwelingetal.,2007;WessmanandJohnson,2006).However,theoptimumcarbon/nitrogen(C/N)ratiofornitrificationexistsattheendofthelastpond,wherethetemperaturemaydropto18Cduringwintermonths.ThenitrificationkineticsoftheMBBRsystemoverlongexposureperiodstoatemperatureof18Chasyettobeinvestigatedandquantified.InstallationofanupgradesystemattheendoffunctioninglagoonswheretheC/Nratioislowwilleliminatetheredundantcarbonremovalthatoccursinupgradenitrifyingsystemsappliedafterthefirstpond.Assuch,post-solidsseparationafteranupgradenitrifyingMBBRinstalledfollowingthelastpondis1DepartmentofCivilEngineering,UniversityofOttawa,Ottawa,Ontario,Canada2JohnMeunierInc.,Montreal,Quebec,Canada*DepartmentofCivilEngineering,UniversityofOttawa,Ottawa,ON,161LouisPasteur,K1N6N5;e-mail:[e-mail]36WaterEnvironmentResearch,Volume86,Number1animportantconsideration;biologicalsolidsgeneratedbytheMBBRunitmaycompromisetheeffluenttotalsuspendedsolids(TSS)concentrationwithrespecttoeffluentsolidsregulations.TheobjectivesofthisresearcharetoquantifythekineticrateofMBBRnitrificationat20,5,and18CforatimeperiodrepresentativeofanorthernwinterandthemassofbiofilmpercarrierandbiofilmdetachmentoftheMBBRsystemat20and18CandinvestigatethecorrelationofanArrhenius