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JournalofHazardousMaterials189(2011)229–234ContentslistsavailableatScienceDirectJournalofHazardousMaterialsjournalhomepage:fluent(POME)ChengFang,SompongO-Thong,KanokwanBoe,IriniAngelidaki∗DepartmentofEnvironmentalEngineering,TechnicalUniversityofDenmark,Building113,DK-2800,Kgs.Lyngby,DenmarkarticleinfoArticlehistory:Received15November2010Receivedinrevisedform18January2011Accepted10February2011Availableonline16February2011Keywords:High-rateanaerobicdigestionUASBEGSBBiogasPalmoilmilleffluentabstractAnaerobicdigestionofpalmoilmilleffluent(POME)anddeoiledPOMEwasinvestigatedbothinbatchassaysandcontinuousreactorexperimentsusingup-flowanaerobicsludgeblanket(UASB)andexpandedgranularsludgebed(EGSB)reactors.ThemethanepotentialdeterminedfrombatchassaysofPOMEanddeoiledPOMEwas503and610mL-CH4/gVS-added,respectively.ForthetreatmentofPOMEincontinuouslyfedreactors,bothinUASBandEGSBreactorsmorethan90%CODremovalcouldbeobtained,atHRTof5days,correspondingtoOLRof5.8gVS/(L-reactor.d).Similarmethaneyieldsof436–438mL-CH4/gVS-addedwereobtainedforUASBandEGSBrespectively.However,fortreatmentofdeoiledPOME,bothUASBandEGSBreactorscouldoperateatlowerOLRof2.6gVS/(L-reactor.d),withthemethaneyieldof600and555mL-CH4/gVS-addedforUASBandEGSB,respectively.ThehighermethaneyieldachievedfromthedeoiledPOMEwasattributedtolowerportionofbiofiberswhicharemorerecalcitrantcomparedtherestoforganicmatterinPOME.TheUASBreactorwasfoundtobemorestablethanEGSBreactorunderthesameOLR,ascouldbeseenfromlowerVFAconcentration,especiallypropionicacid,comparedtotheEGSBreactor.©2011ElsevierB.V.Allrightsreserved.1.IntroductionTheproductionofpalmoilisincreasingeveryyearduetoitsapplicationforbiodieselproduction.Thisleadstotheincreasingamountofpalmoilmilleffluent(POME);aby-productsfromtheoil-palmextractingprocess[1].Malaysiaistheworld’slargestpalmoilproducer,withmorethan40milliontonsofPOMEproducedeveryyear[2].42.7milliontonsofpalmoilwasproducedgloballyinyear2008[3].Foreverytonofpalmoilproduced,2.5tonsofPOMEisgenerated[4].POMEisaviscousbrownliquidwithfinesuspendedsolids,pHranginginbetween3.5and4.2withhighcontentofCOD(16–100gCOD/L)andlipid(10–17g/L)[5,6].DeoiledPOMEisathinbrownliquid,obtainedfromaprocessstepwherePOMEisclarifiedbyremovingfloatingfatsandsettlingorganicparticlesinade-oilingtankatHRTof1.5days.Atthisclarificationprocess,mostofparticlesandfloatingfatsareremovedfromPOME,andpartsoftheorganicmatterinPOMEarehydrolysed/fermentedresultinginVFAproduc-tion.DeoiledPOMEcontainshighcontentofVFA(6–8g/L),butlowlipid(2–3g/L)andlowsuspendedsolids(5–7g/L)[4].Thongetal.[7]reportedmethanepotentialofPOMEaround45m3methane/m3ofPOME,correspondingtoabiogasenergypotentialof18GWhperyearforutilizationoftheMalaysianPOME.∗Correspondingauthor.Tel.:+4545251429;fax:+4545932850.E-mailaddresses:ria@env.dtu.dk,ria@er.dtu.dk(I.Angelidaki).Anaerobicdigestion(AD)ofPOMEispreferablecomparedtoaerobictreatmentduetotheenergyproductionfrombiogas[2].ThedigestedsludgefromADprocesscouldalsobeusedasfertilizerforoil-palmplantation[8].However,high-rateanaerobicdigestionofPOMEhasstillnotbeenwidelyapplied.ThemainpracticeoftreatingPOMEisbystorage/treatmentinpondsand/oropenfacul-tativetanksystems[9].However,treatmentofPOMEinponds/opentanksrequireslongretentiontimeandlargetreatmentareas,caus-ingodourgenesandenvironmentalloadduetogasemissionsandleachatecontaminationtogroundwater[9,10].Inordertoshortentheretentiontime,reducethetreatmentarea,andcapturethebio-gasforenergyutilization,high-rateanaerobicdigestionhasgainedincreasedattention.Anaerobicdigestionisamulti-stagedegradationoforganiccom-poundsthroughavarietyofintermediatesintomethaneandcarbondioxide,bytheactionofaconsortiumofmicroorganisms[11].Sinceanaerobicbacteriahavegenerallylowgrowthrates,immo-bilisedreactorssystemsgivethepossibilitytooperatewithhigherflows.Twowidelyusedhigh-ratereactortypesareupflowanaer-obicsludgeblanket(UASB)andexpandedgranularsludgebed(EGSB)reactors,wherebiomassisimmobilisedindensegranularbiomassassociations.EGSBreactorisavariantoftheUASBconceptwiththelargerratioofreactorheight/surfaceareatoobtainhigherupflowvelocityandthusimprovethecontactbetweensubstrateandbiomass[12].ThepotentialofusingUASBreactorfortreatingPOMEhaspre-viouslybeendemonstrated[13].POMEtreatmenthasbeentested0304-3894/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.doi:10.1016/j.jhazmat.2011.02.025230C.Fangetal./JournalofHazardousMaterials189(2011)229–234Table1CharacteristicsofPOMEanddeoiledPOME.ComponentUnitRawPOMEDeoiledPOMEpH4.34.7TSg/L67.319.7VSg/L57.312.9TSSg/L40.65.36VSSg/L34.50.42TotalCODg/L9745SolubleCODg/L8834Lipidg/L8.42.67Alkalinitymg/L14885EthanolmM12.453.91AceticacidmM52.6265.77PropionicacidmM0.7818.57ButyricacidmM0.1820.44TotalVFAg/L3.36.75TKNg/L3.20.45ina10LUASBreactor.CODremovalof96%wasobtainedattheOLRof2.5gCOD/(L-reactor.d)withinfluentCODconcentrationof50g/LandHRT20days.However,whentheorganicloadingrateapproached17.5gCOD/(L-reactor.d)withHRT3days,theprocessbecame
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