DesignoperationofMBBRreactors

DesignandoperationsoftheKaldnesmovingbedbiofilmreactorsBjornRustena,*,BjørnarEikebrokkb,YngveUlgenesb,EivindLygrencaAquateam—NorwegianWaterTechnologyCentre,P.O.Box6875,Rodelokka,N-0504Oslo,NorwaybSINTEFWaterandEnvironment,Klaebuveien153,N-7465Trondheim,NorwaycBiodesign,Raschsvei78,N-1185Oslo,NorwayReceived26December2004;accepted18April2005AbstractThemovingbedbiofilmreactor(MBBR)wasdevelopedinNorwayinthelate1980sandearly1990s.Itiscoveredbyseveralpatentsandhasbeenahugesuccessworld-widefortreatmentofmunicipalandindustrialwastewaters.Inaddition,MBBRshavebeensuccessfullyusedforbiologicaltreatmentofdrinkingwateraswellasforwatertreatmentinfishfarms.TheMBBRsuseplasticbiofilmcarriersofauniquedesign,tomaximizetheactivebiofilmsurfaceareainthereactors.Reactorshaveinsignificantheadloss,noneedforperiodicbackwashingandnosusceptibilityforclogging.ThispaperdescribesthefundamentalsoftheMBBR.Ithasamajoremphasisonnitrificationwiththetypeofbiofilmcarrierusedinfishfarms,butbrieflytouchesuponremovaloforganicmatteranddenitrification.MajorfactorsinfluencingthenitrificationratesinMBBRsarediscussedindetail.Resultsfromsmall-scaleMBBRtests,aswellasfromcommerciallyoperatedMBBRsatfullscalefishfarmsarepresented.Thedataarefrombothfreshwaterandmarineapplications.#2005ElsevierB.V.Allrightsreserved.Keywords:Biofilmcarriers;Biologicaltreatment;Freshwatersystems;Marinesystems;Nitrification1.IntroductionForbiologicaltreatmentofwater,therearemanydifferentbiofilmsystemsinuse,suchastricklingfilters,rotatingbiologicalcontactors(RBC),fixedmediasubmergedbiofilters,granularmediabiofilters,fluidisedbedreactors,etc.Theyallhavetheiradvantagesanddisadvantages.Thetricklingfilterisnotvolume-effective.MechanicalfailureshaveoftenbeenexperiencedwiththeRBCs.Itisdifficulttogetevendistributionoftheloadonthewholecarriersurfaceinfixedmediasubmergedbiofilters.Thegranularmediabiofiltershavetobeoperateddiscontinuouslybecauseoftheneedforbackwashingandmanyofthefluidisedbedreactorsshowhydraulicinstability.Forthesereasons,themovingbedbiofilmreactor(MBBR)process(EuropeanPatentno.0,575,314,USPatentno.5,458,779)wasdevelopedinNorwayinthelate1980sandearly1990s(Ødegaardetal.,1994,1999).TheMBBRhasbeenacommercialsuccess.Therearepresentlymorethan400large-scalewastewater(2006)322–331*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](B.Rusten).0144-8609/$–seefrontmatter#2005ElsevierB.V.Allrightsreserved.doi:10.1016/j.aquaeng.2005.04.002treatmentplantsbasedonthisprocessinoperationin22differentcountriesallovertheworld.Inadditionthereareseveralhundredsmall,on-sitetreatmentunitsbasedontheMBBR—mostoftheseinGermany.Morethan50MBBRplantsareinoperationatcommercialfishfarms,inadditiontoseveralhundredsmallMBBRsystemsforornamentalfish.ThispaperdescribesthefundamentalsoftheMBBRandthedesignanduseofMBBRsinfishfarms.Ithasamajoremphasisonnitrification,butbrieflytouchesuponremovaloforganicmatteranddenitrification.Resultsfromsmall-scaleMBBRtests,aswellasfromcommerciallyoperatedMBBRsatfullscalefishfarmsarepresented.2.TheKaldnesmovingbedbiofilmreactorprocess2.1.DescriptionofreactorsandbiofilmcarriersTheideabehindthedevelopmentoftheKaldnesMBBRprocesswastoadoptthebestfeaturesoftheactivatedsludgeprocessaswellasthoseofthebiofilterprocesses,withoutincludingtheworst.Contrarytomostbiofilmreactors,theMBBRutilisesthewholetankvolumeforbiomassgrowth.Italsohasaverylowhead-loss.Contrarytotheactivatedsludgereactor,itdoesnotneedanysludgerecycle.Thisisachievedbyhavingthebiomassgrowoncarriersthatmovefreelyinthewatervolumeofthereactorandthatarekeptwithinthereactorvolumebyasievearrangementatthereactoroutlet.Thereactormaybeusedforaerobic,anoxicoranaerobicprocesses,asillustratedinFig.1.Inaerobicprocesses,thebiofilmcarriermovementiscausedbytheagitationsetupbytheair,whileinanoxicandanaerobicprocessesamixer(normallyahorizontalshaftmountedbananamixer)keepsthecarriersmoving.Fortheaerobicreactors,aspecialcoarsebubbleaerationsystemhasbeendeveloped.Specialsievearrangementstoretainthebiofilmcarrierswithinthereactorshavealsobeendeveloped.Thismaybeverticallymounted,rectangularmeshsieves,butlatelythesieveismoreoftenshapedasacylindricalbarsieve,verticallyorhorizontallymounted.ProperdesignofaerationgridsandsievesisveryimportantforoptimumperformanceoftheMBBRprocess.Basedoncomprehensiveandsystema-tictesting,detailedguidelinesforaerationandsievedesignhavebeenestablishedandareproprietaryinformationoftheAnoxKaldnescompanies.Oneimportantadvantageofthemovingbedbiofilmreactoristhatthefillingfractionofbiofilmcarriersinthereactormaybesubjecttopreferences.Inordertobeabletomovethecarriersuspensionfreely,itisrecommendedthatfillingfractionsshouldbebelow70%.Onemay,however,useasmuchasneededbelowthis.AnumberofdifferentcarriershavebeendevelopedbyAnoxKaldnes.DataforthethreesmallestcarriersarelistedinTable1andFig.2showsaphotoofthesecarriers.Mostplants,andallthefishfarmplantsreferredtointhispaper,usetheoriginalKaldnesK1carrier.Thecarriersaremadeofpolyethylene(PEHD)withadensityof0.95g/cm3.Sincethebiomassis