Aerobicmovingbedbiofilmreactortreatingthermomechan

WaterResearch36(2002)1067–1075AerobicmovingbedbiofilmreactortreatingthermomechanicalpulpingwhitewaterunderthermophilicconditionsSigrunJ.Jahrena,*,JukkaA.Rintalab,HallvardØdegaardaaDepartmentofHydraulicandEnvironmentalEngineering,NorwegianUniversityofScienceandTechnology,N-7034Trondheim,NorwaybDepartmentofBiologicalandEnvironmentalScience,UniversityofJyv.askyl.a,P.O.Box35,FIN-40351Jyv.askyl.a,FinlandReceived20April1999;receivedinrevisedform17April2001;accepted15June2001AbstractThecontinuouslyoperatedlaboratoryscaleKaldnesmovingbedbiofilmreactor(MBBR)wasusedforthermophilic(551C)aerobictreatmentofTMPwhitewater.IntheMBBR,thebiomassisgrownoncarrierelementsthatmovealongwiththewaterinthereactor.Inoculationwithmesophilicactivatedsludgegave60–65%SCODremovalfromthefirstdayonwards.Duringthe107daysofexperiment,the60–65%SCODremovalswereachievedatorganicloadingratesof2.5–3.5kgSCODm
3d
1,thehighestloadingratesappliedduringtherunandHRTof13–22h.Carbohydrates,whichcontributedto50–60%oftheinfluentSCOD,wereremovedby90–95%,whilelessthan15%ofthelignin-likematerial(30–35%ofSCODin)wasremoved.Thesludgeyieldwas0.23gVSSgSCODremoved
1.Theresultsshowthattheaerobicbiofilmprocesscanbesuccessfullyoperatedunderthermophilicconditions.r2002ElsevierScienceLtd.Allrightsreserved.Keywords:Aerobic;Biofilm;Movingbedbiofilmreactor;Thermophilic;Thermomechanicalpulpingwhitewater1.IntroductionThermomechanicalpulp(TMP)isproducedbyrefiningwoodchipsattemperaturesabove1001C.TheyieldoftheTMPprocessis93–97%basedondrywood[1]implyingthat30–70kgton
1islosttothewater.TheorganiccompoundsinTMPwhitewaterconsistoflignin(40%),carbohydrates(40%)andextractives(20%)[2].Thermomechanicalpulpingwhitewateriswarm,nor-mallywithtemperaturesbetween501Cand801C,withaCODof1000–5600mgL
1[3].Processwatertreatmentathightemperaturewouldomitcoolingoftheprocesswaterandallowthetreatedwatertobereusedintheprocessesatthemillwithoutheating.Thus,investmentsincoolingfacilitiessuchascoolingtowersmaybeminimisedorevenavoided.Highermaintenanceenergyrequirementsandhighermicrobialdecaycoefficientsforthermophilesindicatethattheamountofexcesssludgewillbesmallerforthermophilicthanformesophilictreatmentprocesses[4–6].Thermophilicaerobictreatmentofpulpandpapermillwastewatersat50–551ChasbeenfoundtobecomparablewithmesophilictreatmentintermsofBODandCODremovalinlaboratoryscaleexperimentsatloadingratesupto8.4kgCODm
3d
1[7–10].Aerobicpost-treatmenthasbeensuccessfullyappliedinlabora-tory-scaleforanaerobicallypre-treatedTMPwhitewateratthermophilicconditions(551C)[11],whilepreviousthermophilicaerobicstudiesonrecirculatednewsprintwithsuspendedgrowthsystemsinlaboratory-scalegavepoororganicremovalefficiencies[12].Sludgefromthetreatmentprocessoperatedat50–531Cshowedbettersettlingcharacteristicscomparedtolowertemperatures[8,10].Thiscouldbeexplainedbydecreasedliquidviscosityathightemperatures[4].Otherplants,how-ever,experiencedlowersettlingratesandlowerBODremovalratesat41–501Cthanat22–351C[13,14].To*Correspondingauthor.Presentaddress:3MINUTESMediaAS,Nygaard,Rute784,2050Jessheim,Norway.E-mailaddress:[e-mail](S.J.Jahren).0043-1354/02/$-seefrontmatterr2002ElsevierScienceLtd.Allrightsreserved.PII:S0043-1354(01)00311-6ourknowledge,aerobicthermophilictreatmentisnotappliedinfullscaleforpulpandpapermillwastewaters,whiletheapplicationsforotherindustrialwastewatersarerare.Saturationvaluesforoxygeninwaterdecreasewhenthetemperatureincreases(6.9mgL
1at351Cversus4.5mgL
1at551C).Thediffusivitycoefficientforoxygen,however,issignificantlyhigheratelevatedtemperatures(2.8e–5cm2s
1at351Cversus4.3e–5cm2s
1at551C;calculatedwithWilke–Changequa-tion).Therateofoxygentransferathightemperaturesshouldthereforebeexpectedtobeasgoodas,orbetterthan,thatatmesophilicconditions.Biofilmtreatmentplantsaremorecompactthanactivatedsludgeplantsandthetreatmentefficienciesarelessdependentonthesludgeseparationcharacter-istics.TheKaldnesmovingbedbiofilmreactor(MBBR)isacompletelymixedcontinuouslyoperatedbiofilmreactorwherethebiomassisgrownonsmallcarrierelementsthatmovealongwiththewaterinthereactor[15,16].Nosludgerecyclingisnecessaryforkeepingthebiomassperunitvolumeatahighlevel.TheKaldnespolyethylenecarrierelementsareshapedlikesmallcylinderswithacrossinsideandlongitudinalfinsontheoutside.Thebulkcarriervolumerelativetoreactorvolumeis40–70%.Thecarriershaveapotentialgrowthareaforabiofilmofabout490m2m
3at70%filling,whiletheefficientgrowthareaiscalculatedtobeabout350m2m
3[16].Themovementinthereactoriscausedbyaerationinanaerobicreactorandbyamechanicalmixerinananaerobicoranoxicreactor.TheMBBRhasbeensuccessfullyappliedunderaerobicandanoxicconditionsforfull-scaletreatmentofmunicipalandindustrialwastewaters[15,16].ExperimentsusingtheMBBRforthetreatmentofconcentratedwastewatersunderthermophilicanaerobicconditionshavebeensuccessfulaswell[17].Theobjectiveofthisstudywastoevaluateinlaboratory-scalethefeasibilityoftheKaldnesaerobicMBBRforthetreatmentofTMPwhitewaterunderthermophilicconditions.2.Materialsandmethods2.1.TMPwhitewaterTheTMPwhitewaterwasobtainedfromaFinnishpulpandpapermillusing