AcouplingmodelforEGSBbioreactorsHydrodynamicsandan

ChemicalEngineeringandProcessing50(2011)316–324ContentslistsavailableatScienceDirectChemicalEngineeringandProcessing:ProcessIntensificationjournalhomepage::HydrodynamicsandanaerobicdigestionprocessesMaurenFuentesa,b,∗,NicolásJ.Scennaa,c,PíoA.Aguirrea,daINGAR-(CONICET-UTN),Avellaneda3657(3000)SantaFe,ArgentinabDeptodeCienciasBásicas-UTNFRSF,Lavaise610(3000)SantaFe,ArgentinacCAIMI-UTNFRR,Zeballos1341(2000)Rosario,ArgentinadFacultaddeIng.Qca,UNL,SantiagodelEstero2829(3000)SantaFe,ArgentinaarticleinfoArticlehistory:Received31January2010Receivedinrevisedform10January2011Accepted23January2011Availableonline1February2011Keywords:DynamicmodelingandsimulationThree-phasesystemsEGSBreactorsWastewatertreatmentabstractTheaimofthispaperistopresentacouplingmodelforcalculatingboththehydrodynamicandanaer-obicdigestionprocessesinexpandedgranularsludgebed(EGSB)bioreactorsfortreatingwastewaters.Thebioreactorismodeledasadynamic(gas–solid–liquid)three-phasesystem.Anexistingsetofexper-imentaldataofthreecasestudiesbasedonthestart-upandoperationalperformanceofEGSBreactorsisusedtoadjustandvalidatethemodel.Anovelparameter,thespecificrateofgranulerupture,isdefinedforcalculatingthebiomasstransportphenomena.Valuesaround1×10−20dmd2g−1arecalculatedforthisparameter.BioreactorperformanceswereanalyzedthroughthemainvariableprofilessuchaspH,COD,VFAandVSSconcentration.Agoodagreementwasobtainedamongexperimentalandpredictedvalues.ItseemstoindicatethattheproposedEGSBmodelisabletoreproducethemainbiologicalandhydrodynamicsuccessesinthebioreactor.©2011ElsevierB.V.Allrightsreserved.1.IntroductionTheexpandedgranularsludgebed(EGSB)reactorisasuperhighratetechnologyforwastewatertreatment.ItwasintroducedbyDeManetal.[1]andhasattainedanincreasingpopularityinthelastdecade[2,3].TheconceptionoftheEGSBreactorcanbeconsideredasanimprovementoftheupflowanaerobicsludgeblanket(UASB)reactordevelopedbyLettingaetal.[3].Intheanaerobicdigestionprocesses,complexorganicsubstratessuchasproteins,lipids,andcarbohydratesarehydrolyzedintosolubleaminoacids,fattyacids,andsugars,followedbythefermenta-tiontoacetate,formate,hydrogen,andcarbondioxidewhicharefinallyutilizedbymethanogenicmicroorganismtoformmethane[4–6].BothEGSBandUASBarebasedontheabilityofmicroorganismtoformdenseaggregatesbyautoimmobilization.However,insidetheEGSBreactor,thehigherupflowvelocities,whicharecausedbyahighrecyclerateandahighheight/diameterratio,causethesludgeexpansionthroughthewholereactorthusimprovingitscontactwiththeeffluentandreducetheunitdeadvolume[7,8].Sincehigherorganicloadingrates(upto40kgofchemicaloxygendemandCODm−3d−1)canbeaccommodatedinEGSB,thegaspro-∗Correspondingauthorat:INGAR-InstitutodeDesarrolloyDise˜no-Avellaneda3657(3000)SantaFe,Argentina.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](M.Fuentes).ductionisalsohigher,improvingevenmorethemixinginsidethereactor.Theexactmixingpatterncannotbegeneralized,anditmustbeevaluatedineachreactorbyassessingthereactorhydrodynam-ics[9].However,afullyexpandedEGSBreactorcanbeconsideredasacompletelymixedtank[10,11],andliquidfilmmasstransferresistanceseemstobenegligible[12].TheknowledgeofthebedexpansionplaysanimportantroleinthedesignandoperationofanEGSBreactor,becauseitisthekeypointtoreachacompromisebetweenbedexpansionandsludgewashout,andthestabilityandperformanceoftheEGSBsystemwouldbesensitivetothedegreeofexpansion[13].Someideasfromsoliddynamicsinathree-phasefluidizedbedreactorcanbeusedtodescribethemultiplesolid–liquid–gasinteractionsthattakeplaceinEGSBreactors.Inpreviousworks,aheterogeneousmodelforthree-phaseanaerobicfluidizedbed(AFB)reactorswasdevelopedandvalidated[14–16].TheaimofthisworkistoapplythismethodologyformodelingEGSBreactors.Thus,aheterogeneousmodelforEGSBbioreactorsispre-sentedhere.Thismodelingapproachcombinesthedynamicsofthethreephasespresentinthereactorincludingbiochemical,physico-chemicalandhydrodynamicprocesses.Severaldetailsofreactordesign,sludgeandwastewatercharacteristics,andopera-tionalconditionsarerequiredformodeladjustmentandvalidation.Almostallworkspublisheddescribebetterthebiochemicalperfor-manceofEGSBreactorsthantheirhydrodynamics.Duetothelackofinformationonsomeparametersthatcanbemeasuredandare0255-2701/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.doi:10.1016/j.cep.2011.01.005M.Fuentesetal./ChemicalEngineeringandProcessing50(2011)316–324317notreported,theauthorsshouldsolvetheinitializationproblemviasimulation,i.e.asensitivityanalysisofmodelresultsrelatedtotheseparametersisrequired.Thepaperisorganizedasfollows:inSection2,mainmathe-maticalequationsoftheglobalmodelarepresented,andsomehypothesesrelatedtothebioparticlemodelandhydrodynamicsarediscussed.ComputationalaspectsofmodelimplementationandsolutionusinggPROMSaredescribedinSection3.Modeladjust-mentandvalidationusinganexistingsetofexperimentaldataofcasestudiesbasedonthestart-upandoperationalperformanceofEGSBreactorsispresentedinSection4.Finally,conclusionsaredrawninSection5.2.MathematicalmodelAsmentio