74英文文献

摘要Anoveloxidationditchsystemusinganaerobictanksandinnovativedualdissolvedoxygen(DO)controltechnologyisproposedforbiologicalnitrogenandphosphorusremovalfromdomesticsewage.Acontinuousbench-scaleexperimentrunningformorethan300dayswasperformedtoevaluatethesystem.MonitoringandcontrollingtheairflowandrecirculationflowrateindependentlyusingDOvaluesattwopointsalongtheditchpermittedmaintenanceofaerobicandanoxiczoneratiosofaround0.30and0.50,respectively.TheabilitytooptimizeaerobicandanoxiczoneratiosusingthedualDOcontroltechnologymeantthatatotalnitrogenremovalefficiencyof83.2–92.9%couldbemaintained.Thisremarkablenitrogenremovalperformanceminimizedthenitraterecycletoanaerobictanksinhibitingthephosphorusrelease.Hence,thetotalphosphorusremovalefficiencywasalsoimprovedandrangedwithin72.6–88.0%.TheseresultsdemonstratedthatstabilizationoftheaerobicandanoxiczoneratiobydualDOcontroltechnologynotonlyresultedinamarkedimprovementofnitrogenremoval,butitalsoenhancedphosphorusremoval.关键词Biologicalnitrogenandphosphorusremoval,dualDOcontroltechnology,oxidationditch介绍Removalofbiologicalnitrogenandphosphorusfromdomesticsewageisanimportantconsiderationforavoidingseriouseutrophicationproblemsinclosedwaterecosystem(Metcalf&Eddy2003).Oxidationditch(OD)technologyisamodifiedactivatedsludgesystemthathasbeenextensivelyappliedfortheremovalofpollutantsgiventheadvantagesassociatedwiththeprocesscharacteristicsandditchconfigurations.Typicaloxidationditchesarecompletelymixedsystems,andhorizontallyorverticallymountedaeratorsprovidecirculationandoxygensupplyintheditchsimultaneously.TheconventionaloxidationditchsystemshavebeencommonlyoperatedwithinfluentBODloading(0.24kgBOD/m3d)andhydraulicretentiontime(HRT)aslongas6–30h(USEPA2000).Sincenitrogenremovalpotentialisdependentupontheaerobicphasefornitrificationandtheanoxicphasefordenitrification,thedissolvedoxygen(DO)distributionintheditchisanimportantcontrolparameterforoptimalnitrogenremoval(Brouweretal.1998;Furukawaetal.1998;Ekmanetal.2006).Surfaceaeratorsmentionedabovehardlyestablishastableanoxiczoneunderthedailyvariationsofinfluentqualityandwatertemperatureduetothesimultaneouschangeincirculationspeedandoxygensupply.Hence,separationofaerationandmixingiseffectiveforstabilizingtheanoxiczone(Haoetal.1997).Itwasalsoreportedthattheefficiencyofremovingnitrogencouldbeincreasedbyanoxidationditchwiththeseparationofthetwofunctionsofaeration(byflatflexiblemembranes)andmixing(byhorizontalmixer)(Roustanetal.1993).Moreover,thecombinationoftheaerationandmixingwillcausehighenergyconsumptionandaperturbationofbiologicalsystemwithoutconsiderationthewastewatercharacteristics.TheDOcontrolsystematonepointmaintainsDOconcentrationsintheaerobicphasewithoutconsiderationoftheremainingDOsubsequentlyenteringtheanoxicphase(Kietal.2008),limitingtherateofdenitrificationinanoxicphaseandincreasingtheenergycostsofmunicipalfacilities(Ekmanetal.2006;Holendaetal.2008).Inthisstudy,theinnovativedualDOcontroltechnologywhichwascapableofcontrollingtheaerationflowandrecirculationrateindependentlywasproposedforoxidationditcheswithfine-bubblediffusersandsubmergedimpellers.ThisnovelsystemcouldeffectivelycontroltheDOconcentrationattwopointsattheoptimallevelforthebiologicalsewagetreatment.Inthisresearch,thetypicaloxidationditchwasreplicatedbyeightcompletelymixedtanksinserieswithhugeinnerrecirculationratesimilartothepreviousstudies(Furukawaetal.1998;Henzeetal.2000).TheobjectiveofthisresearchwastoevaluatethenoveloxidationditchprocessemployingdualDOcontroltechnologyandanaerobictankspriortotheditchforthebiologicalnitrogenandphosphorusremoval.材料和方法反应器的安装和操作Thebench-scaleoxidationditchsystemshowninFigure1wasspecificallydesignedandoperatedtoachievesimultaneousnitrogenandphosphorusremovalfromdomesticsewageinKochiPrefecture,Japan.Thecorereactorwithaworkingvolumeof300Lwasdividedintoeightcompletelymixedtanks.Forbiologicalphosphorusremoval,oneortwoanaerobictanks(eachtankwas37.5L)wereinstalledupstreamfromthemainditch.Thetracertestsindicatedthatthecorereactorconsistingoftheserialcompletelymixedtankswithhugeinnerrecirculationratereplicatedtheflowcharactersandhydrodynamiccharacteristicsoftypicaloxidationditch.Thegridchambereffluentwasstoredinastoragetankfromwhereitwasfedintotheanaerobictanksafterfiltrationthroughascreenwith2mmdiameter.Themixedliquorthenflowedthroughtoaseriesofeightmixedtanksbeforeenteringthesedimentationtank(151L).Thereturnsludgewasthenpumpedfromthesedimentationtankintotheanaerobictankstoretainthebiomasswithinthesystem.ContinuoustreatmentofrealdomesticsewagewasconductedfortheevaluationofthenoveloxidationditchfromJune2007toApril2008.TheoperationalperiodwasdividedintoseveralrunsbydifferentoperatingconditionsassummarizedinTable1indetails.Thehugeinnerrecirculationratiosintherangeof45–78suggestedthattheexperimentalsetupwascapableofreplicatingthetypicaloxidationditches.ExceptforthefourthtankinRUN16,aerationwasperformedinthe5thtankinmostexperimentalruns.HRTwasmaintainedatapproximately11hforthenoveloxidationditchprocesswhichwasconsiderablyshorterthantheHRTemp