Bacterialtransformationandbiodegradationprocessess

BacterialtransformationandbiodegradationprocessessimulationinhorizontalsubsurfaceflowconstructedwetlandsusingCWM1-RETRASOEstherLlorensa,⇑,MaartenW.Saaltinkb,ManelPocha,c,JoanGarcíadaCatalanInstituteforWaterResearch,H2OBuilding,ScientificandTechnologicalParkoftheUniversityofGirona,c/EmiliGrahit101,E-17003Girona,SpainbDepartmentofGeotechnicalEngineeringandGeosciences,TechnicalUniversityofCatalonia,c/JordiGirona1–3,MòdulD-2,E-08034Barcelona,SpaincChemicalandEnvironmentalEngineeringLaboratory(LEQUIA),UniversityofGirona,CampusMontilivis/n,E-17071Girona,SpaindEnvironmentalEngineeringDivision,DepartmentofHydraulic,MaritimeandEnvironmentalEngineering,TechnicalUniversityofCatalonia,c/JordiGirona1–3,MòdulD-1,E-08034Barcelona,SpainarticleinfoArticlehistory:Received9June2010Receivedinrevisedform8September2010Accepted9September2010Availableonline17September2010Keywords:BiochemicalpathwaysNumericalsimulationReedbedsTreatmentwetlandsWastewatertreatmentabstractTheperformanceandreliabilityoftheCWM1-RETRASOmodelforsimulatingprocessesinhorizontalsub-surfaceflowconstructedwetlands(HSSFCWs)andtherelativecontributionofdifferentmicrobialreac-tionstoorganicmatter(COD)removalinaHSSFCWtreatingurbanwastewaterwereevaluated.Variousdifferentapproacheswithdiverseinfluentconfigurationsweresimulated.Accordingtothesimulations,anaerobicprocessesweremorewidespreadinthesimulatedwetlandandcontributedtoahigherCODremovalrate[72–79%]thananoxic[0–1%]andaerobicreactions[20–27%]did.Inallthecasestested,thereactionthatmostcontributedtoCODremovalwasmethanogenesis[58–73%].Allresultsprovidedbythemodelwereinconsonancewithliteratureandexperimentalfieldobservations,suggestingagoodperformanceandreliabilityofCWM1-RETRASO.Accordingtothegoodsimulationpredictions,CWM1-RETRASOisthefirstmechanisticmodelabletosuccessfullysimulatetheprocessesdescribedbytheCWM1modelinHSSFCWs.2010ElsevierLtd.Allrightsreserved.1.IntroductionHorizontalsubsurfaceflowconstructedwetlands(HSSFCWs)areessentiallyfixedbiomassreactorsinwhichwastewatercon-taminantsareremovedortransformedbyalargenumberofphys-ical,chemicalandbiologicalprocessesthatoccurinparallelandinfluenceeachother.Inurbanwastewatertreatmentbiodegrada-tionandtransformationprocessesrelatedtocarbon,nitrogenandsulphurcompoundshavebeentheobjectofawiderangeofre-searchstudies(Faulwetteretal.,2009;Langergraberetal.,2009).Alargenumberofthemhavedemonstratedthatorganicmatterandtotalsolidsremovaloccursmainlyneartheinletzoneduetophysicalandchemicalprocessesthatretainandentrapparticulatematterintheconstructedwetlandmatrix(KadlecandKnight,1996;Pedescolletal.,2009).Biologicalprocesses,inturn,areresponsibleforthedegradationofsolidsretainedinthegranularmediumandofdissolvedorganicmatter,nitrogen,andsulphurcompounds(Ojedaetal.,2008).Thescientificcommunitynowac-ceptsthatinHSSFCWsthisdegradationoccursthroughseveralbiochemicalpathways,whichcantakeplaceatthesametimebutatdifferentlocations(Faulwetteretal.,2009;Garcíaetal.,2005).Theexistenceofmicrositeswithdifferentredoxconditionsmakesthispossible(Cooperetal.,1996;Faulwetteretal.,2009).However,therelativeimportanceofbiochemicalpathwaysmaychangeovertimeandspacedependingonsomefactorssuchasthehydraulicloadingrate(HLR),theredoxpotentialandtheavail-abilityofterminalelectronacceptors.Accordingtothespecificenvironmentalconditions,theactivityofaspecificmicrobialfunc-tionalgroupwillbehigherthanthatoftheothermicrobialfunc-tionalgroupspresentinthewetland,promotingtheremovalofaparticularpollutant(Faulwetteretal.,2009).Recentstudieshaveshownthataerobicrespirationplaysonlyaminorroleorisjustoneofmanymicrobialreactionsthatcontributetotheoverallor-ganicmatterdecomposition(Baptistaetal.,2003;Garcíaetal.,2004b).Generally,anaerobicprocesseswouldplayamajorroleinHSSFCWs(Langergraber,2008;Langergraberetal.,2009).InHSSFCWstheinteractionsbetweenwater,thegranularmed-ia,macrophytes,litteranddetritus,andmicroorganismsareverycomplex(Ojedaetal.,2008).ThiscomplexitymakesdifficulttounderstandindetailhowHSSFCWsfunction.Modellinghasbe-comeapowerfultooltobetterunderstandtheperformanceofwastewatertreatmentsystems,includingHSSFCWs.ForalongtimeHSSFCWshavebeenthoughtofas‘‘blackboxes”,designedtofunctionbasedonconcentrationchangesofselectedinfluentandeffluentparameters(Linetal.,2008).Theremovalmechanisms0960-8524/$-seefrontmatter2010ElsevierLtd.Allrightsreserved.doi:10.1016/j.biortech.2010.09.038⇑Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddresses:[e-mail](E.Llorens),[e-mail](M.W.Saaltink),[e-mail],[e-mail](M.Poch),[e-mail](J.García).BioresourceTechnology102(2011)928–936ContentslistsavailableatScienceDirectBioresourceTechnologyjournalhomepage:(Kadlec,2003;KadlecandKnight,1996;Rousseauetal.,2004).Mechanisticmathemati-calmodelsthatdescribethetransformationandremovalprocessestakingplacewithinHSSFCWsarepromisingtools.Thedevelop-mentofmechanisticmodelsdescribingprocessesinHSS