StateOfTheArtInEuropeOfTheMovingBedBiofi

WEFTEC®2004STATEOFTHEARTINEUROPEOFTHEMOVINGBEDBIOFILMREACTOR(MBBR)PROCESSHallvardØdegaard1,BjørnRustenandFlemmingWessman1NorwegianUniversityofScienceandTechnology(NTNU)DepartmentofHydraulicandEnvironmentalEngineeringNO-7491Trondheim,NORWAYABSTRACTThepaperdescribesthemovingbedbiofilmreactor(MBBR)andpresentsapplicationsofwastewatertreatmentprocessesinwhichthisreactorisused.TheMBBRprocesseshavebeenextensivelyusedforBOD/COD-removalaswellasfornitrificationanddenitrificationinmunicipalaswellasindustrialwastewatertreatment.Thispaperfocusesonthemunicipalapplications.Themostfrequentprocesscombinationsarepresentedanddiscussed.Basicdesigndataobtainedthroughresearchaswellasdatafrompracticaloperationofvariousplantsarepresented.ItisdemonstratedthattheMBBRmaybeusedinanextremelycompacthigh-rateprocess(1htotalHRT)forsecondarytreatment.MostEuropeanplantsrequireP-removalandperformancedatafromplantscombiningMBBRandchemicalprecipitationispresented.LikewisedatafromplantsinItalyandSwitzerlandthatareimplementingnitrificationinadditiontosecondarytreatmentarepresented.TheresultsfromthreeNorwegianplantsthatareusingtheso-calledcombineddenitrificationMBBRprocessarediscussed.Nitrificationratesashighas1.2gNH4-N/m2.datcompletenitrificationweredemonstratedinpracticaloperationatlowtemperatures(11oC),whiledenitrificationrateswereashighas3.5gNO3-Nequiv./m2.d.Dependingontheextentofpre-treatment,thetotalHRToftheMBBRforN-removalwillbeintherangeof3-5hrs.KEYWORDSWastewater,treatment,movingbedprocess,experiencesINTRODUCTIONBiofilmprocessesareincreasinglybeingfavouredinsteadofactivatedsludgeprocesses.Thereareseveralreasonsforthis,suchas:a.Thetreatmentplantrequireslessspace(animportantcostfactor)b.Thefinaltreatmentresultislessinfluencedbybiomassseparationsincethebiomassconcentrationtobeseparatedisatleast10timeslowerandthereisgreaterflexibilitywithrespecttochoiceofbiomassseparationmethod(i.e.compactflotationorfiltration)c.Theattachedbiomassbecomesmorespecialised(higherconcentrationofrelevantorganisms)atagivenpointintheprocesstrain,becausethereisnobiomassreturnTherearealreadymanydifferentbiofilmsystemsinuse,suchastricklingfilters,rotatingbiologicalcontactors(RBC),fixedmediasubmergedbiofilters,granularmediabiofilters,fluidisedbedreactorsetc.Theyhavealltheiradvantagesanddisadvantages.Thetricklingfilterisnotvolume-effective.MechanicalfailuresareoftenexperiencedwiththeRBCs.Itisdifficulttogetevendistributionoftheloadonthewholecarriersurfaceinfixedmediasubmergedbiofilters.Thegranularmediabiofiltershavetobeoperateddiscontinuouslybecauseoftheneedforbackwashingandthefluidisedbedreactorsshowhydraulicinstability.Forthesereasonsthemovingbedbiofilmreactorprocess(Eur.pat.no.0575314,USpat.no.5,458,779)wasdevelopedinNorwayinthelate80’iesandearly90’ties(Ødegaardetal,1994,Ødegaardetal,1999).Therearepresentlymorethan300treatmentplantsbasedonthisprocessinoperationorunderconstructionin22differentcountriesallovertheworld.Inadditionthereareseveralhundredon-sitetreatmentunitsbasedontheMBBR–mostoftheseinGermany.InEuropemostofthelargerplantsareinoperationintheScandinaviancountries,GreatBritain,ItalyandSwitzerlandeventhoughthereareplantsin17Europeancountries.TheMBBRplantsareusedformunicipal-aswellasforvarioustypesofindustrialwastewatertreatment.Ithasalsobeenusedforbiologicaldrinkingwatertreatmentaswellaswatertreatmentinfish-farming.Thispaperwillfocusonmunicipalwastewatertreatmentapplications.DESCRIPTIONOFTHEMOVINGBEDBIOFILMREACTOR(MBBR)TheideabehindthedevelopmentoftheMBBRprocesswastoadoptthebestfeaturesoftheactivatedsludgeprocessaswellasthoseofthebiofilterprocesswithoutincludingtheworst.Contrarytomostbiofilmreactors,theMBBRutilisesthewholetankvolumeforbiomassgrowth,asdoesalsotheactivatedsludgereactor.Contrarytotheactivatedsludgereactor,however,itdoesnotneedanysludgerecycle,asisalsothecaseinotherbiofilmreactors.Thisisachievedbyhavingthebiomassgrowoncarriersthatmovefreelyinthewatervolumeofthereactor,keptwithinthereactorvolumebyasievearrangementatthereactoroutlet.Sincenosludgerecirculationtakesplace,onlythesurplusbiomasshastobeseparated-aconsiderableadvantageovertheactivatedsludgeprocess.Thereactormaybeusedforbothaerobic,anoxicoranaerobicprocesses,seeFigure1.Fig.1-PrincipleoftheMBBRandshapeoftheoriginalbiofilmcarrier(K1)a.Aerobicreactorb.Anoxicandanaerobicreactorc.Thebiofilmcarrier(K1)Inaerobicprocesses,thebiofilmcarriermovementiscausedbytheagitationsetupbytheair,whileinanoxicandanaerobicprocessesamixer(normallyahorizontalshaftmountedbananamixer)keepsthecarriersmoving.Intheaerobicreactorsaspecialcoarsebubbleaerationsystemhasbeendeveloped.Thecarriersarekeptwithinthereactorbyanoutletsieve.Thismaybeverticallymounted,rectangularmeshsieves,butlatelythesieveismoreoftenshapedasacylindricalbarsieve,verticallyorhorizontallymounted.Fig.2–PhotosofMBBRreactorsunderconstructiona.Aerobicreactorwithaerationsystemandb.AnoxicreactorwithhorizontallymountedverticallymountedcylindricalbarsievesshaftmixersandrectangularmeshsievesTheoriginalandmostlyusedbiofilmcarrier(K1)ismadeofhighdensitypolyethylene