Biofilmreactorsforindustrialbioconversionprocesses

BioMedCentralPage1of21(pagenumbernotforcitationpurposes)MicrobialCellFactoriesOpenAccessReviewBiofilmreactorsforindustrialbioconversionprocesses:employingpotentialofenhancedreactionratesNasibQureshi*1,BassamAAnnous2,ThaddeusCEzeji3,PatrickKarcher3andIanSMaddox4Address:1NationalCenterforAgriculturalUtilizationResearch,UnitedStatesDepartmentofAgriculture**,AgriculturalResearchService,FermentationBiotechnologyUnit,1815NUniversityStreet,Peoria,IL61604,USA,2EasternRegionalResearchCenter,UnitedStatesDepartmentofAgriculture,AgriculturalResearchService,600EMermaidLane,Wyndmoor,PA19038,USA,3UniversityofIllinois,Biotechnology&BioengineeringGroup,DepartmentofFoodScience&HumanNutrition,1207WGregoryDrive,Urbana,IL61801,USAand4MasseyUnivesity,InstituteofEngineering&Technology,PalmerstonNorth,NewZealandEmail:NasibQureshi*[e-mail];[e-mail];[e-mail];[e-mail];[e-mail]*CorrespondingauthorAbstractThisarticledescribestheuseofbiofilmreactorsfortheproductionofvariouschemicalsbyfermentationandwastewatertreatment.Biofilmformationisanaturalprocesswheremicrobialcellsattachtothesupport(adsorbent)orformflocs/aggregates(alsocalledgranules)withoutuseofchemicalsandformthicklayersofcellsknownasbiofilms.Asaresultofbiofilmformation,celldensitiesinthereactorincreaseandcellconcentrationsashighas74gL-1canbeachieved.Thereactorconfigurationscanbeassimpleasabatchreactor,continuousstirredtankreactor(CSTR),packedbedreactor(PBR),fluidizedbedreactor(FBR),airliftreactor(ALR),upflowanaerobicsludgeblanket(UASB)reactor,oranyothersuitableconfiguration.InUASBgranularbiofilmparticlesareused.Thisarticledemonstratesthatreactorproductivitiesinthesereactorshavebeensuperiortoanyotherreactortypes.Thisarticledescribesproductionofethanol,butanol,lacticacid,aceticacid/vinegar,succinicacid,andfumaricacidinadditiontowastewatertreatmentinthebiofilmreactors.Asthetitlesuggests,biofilmreactorshavehighpotentialtobeemployedinbiotechnology/bioconversionindustryforviableeconomicreasons.Inthisarticle,variousreactortypeshavebeencomparedfortheabovebioconversionprocesses.IntroductionBiochemicalreactorsplayanimportantroleinthebio-chemicalindustryastherateofreaction,ease,andlengthofreactoroperationaffectreactorproductivitiesandhenceprocesseconomics[1,2].Inordertoemployamostappropriatereactorforanindustrialoperation,reactionrateshouldbehighandthereactorconfigurationshouldbesimple.UnderoptimizedparameterssuchaspH,tem-perature,substrate,andmediumcomponents,reactionratecanbeincreasedbyincreasingcellmassconcentra-tioninthereactor.Therearetwomethodscommonlyusedforincreasingcellmassconcentrationinsidethereactor;first,useofapermeablemembranetoretaincells;andtheother,useofimmobilizedcelltechnique.Mem-branereactorsallowpassingofliquid,substrate,andproductoutofthereactorwhileretainingthecells.Inthesereactors,highcellconcentrationscanbeachieved[3].Unfortunately,forsomeprocessessuchaswastewaterPublished:25August2005MicrobialCellFactories2005,4:24doi:10.1186/1475-2859-4-24Received:29June2005Accepted:25August2005Thisarticleisavailablefrom:©2005Qureshietal;licenseeBioMedCentralLtd.ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense(),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.MicrobialCellFactories2005,4:24(pagenumbernotforcitationpurposes)treatment,thesereactorsarenotpreferredduetotheirhighcostandproblemswithfouling.Otherprocesseswheretherelativelyhighcostofthesereactorsdoesnotallowtheiruseincludeproductionoflargevolume,lowcostchemicalssuchasvinegaroraceticacid.Othertypesofreactorsthatofferhighreactionratesareimmobilizedcellreactors[4].Inthesereactors,highcellconcentrationsareachievedbyfixingthemonvarioussupports.Cellscanbeimmobilizedbythreedifferenttechniques;namely,adsorption,entrapment,andcova-lentbondformation.Entrapmentandcovalentbondfor-mationrequireuseofchemicalsthataddtothecostofproductionandperhapsrestrictfurtherpropagationorincreaseincellconcentrationinsidethereactor.Thethirdtechniqueisofnaturaloriginascellsadsorb/andadheretothesupportnaturallyandfirmly[4-6].Thistechniqueiscalledadsorptionandhasbeenusedextensivelyintheliteraturetoadsorbmicrobialcells.Table1showsacom-parisonofthesetechniqueswiththemembranereactors.Itshouldbenotedthatsomemicrobialcellsleachoutfromimmobilizedcellreactorswhichrequireseparation(leachedoutcellsinreactoreffluent)priortoproductremovalpossiblybycentrifugation.Inadditiontobeinganaturalprocess,adsorptioncanbeperformedinplace,andeconomicaladsorbentsareavail-able.Additionally,thesereactorsaresimpleinconceptandconstructionandtheimmobilizationprocessiseco-nomical.Adsorbedcellsformcelllayersonthesupportandcellmassgrowsinsidethereactorovertime[7].Theselayersofcellsarecalledbiofilms.Biofilmscanbeusedinvari