搜索
ReviewAreviewonnumerousmodelingapproachesforeffective,economicalandecologicaltreatmentwetlandsJ.L.G.Kumar,Y.Q.Zhao*CentreforWaterResourcesResearch,SchoolofArchitecture,LandscapeandCivilEngineering,UniversityCollegeDublin,Newstead,Belfield,Dublin4,IrelandarticleinfoArticlehistory:Received17December2009Receivedinrevisedform18October2010Accepted9November2010Availableonline4December2010Keywords:ConstructedwetlandsReedbedRateconstantKineticsBlack-boxmodelProcess-basedmodelabstractConstructedwetlands(CWs)forwastewatertreatmenthaveevolvedsubstantiallyoverthelastdecadesandhavebeenrecognizedasaneffectivemeansof“greentechnology”forwastewatertreatment.Thispaperreviewsthenumerousmodelingapproachesrangingfromsimplefirst-ordermodelstomorecomplexdynamicmodelsoftreatmentbehaviourinCWs.ThemainobjectiveofthemodelingworkistobetterunderstandtheprocessinCWsandoptimizedesigncriteria.Abriefstudyinthisreviewdiscussestheeffortstakentodescribetheprocess-basedmodelfortheefficientremovalofpollutantsinCWs.ObtainingbetterinsightsisessentialtounderstandthehydraulicandbiochemicalprocessesinCWs.Currently,employedmodelingapproachescanbeseenintwocategories,i.e.“black-boxmodels”and“process-basedmodels”.Itisevidentthatfuturedevelopmentinwetlandtechnologywilldependonimprovedscientificknowledgeofinternaltreatmentmechanisms.2010ElsevierLtd.Allrightsreserved.1.IntroductionIndustrialization,urbanizationandinadequatedisposalprac-ticesprecedeamammothpollutionprobleminwaterenvironmentincludingrivers,estuaries,lakesandoceans(Zhaoetal.,2009).Oneofthesustainablewastewatertreatmentalternativesistheimple-mentationofCWssincetheyareefficient,low-cost,easytouseandeco-friendly(Nazetal.,2009).Comparedwithnaturalwetlandswhichhavelargevariabilityinfunctionalcomponentsandthusunknownandunstabletreatmentcapability,CWscanbebuiltwithamuchhigherdegreeofcontrol,thusallowingtheestablishmentofexperimentaltreatmentfacilitieswithawell-definedcompositionofsubstrate,typeofvegetationandflowpattern.Assuch,CWsareoftentermedas“engineeredwetlands”(Knightetal.,1999;Haberletal.,2003;Babatundeetal.,2009).PollutantsinCWsareremovedthroughacombinationofphysical,chemical,andbiolog-icalprocessesincludingsedimentation,precipitation,adsorption,assimilationbytheplanttissueandmicrobialtransformations.ThemainadvantagesofusingCWsareflexibilityinsizingandsiteselection,controloverhydraulicpathwaysandretentiontime.Inadditiontothis,CWsarewellrecognizedashavinglowconstructionandmaintenancecostandlowenergyrequirement.However,ithastobenotedthatCWsarealandintensivetreatmentoptionandshowinsomeextendastochasticbehaviour(Haberletal.,2003).TreatmentbehaviourinCWsisoftenconsideredtobefigurativeblack-box(Rousseauetal.,2004).DetailedunderstandingofCWfunctioningisstilldesirablebecausealargenumberofphysical,chemicalandbiologicalprocessesoccurinparallelandinfluenceeachother.Untilnow,CWsdesignhasbeenmainlybasedonrulesofthumbapproachesusingspecificsurfaceareaofrequirements(BrixandJohansen,2004)orsimplefirst-orderdecaymodels(KadlecandKnight,1996;Rousseauetal.,2004).TheincreasingapplicationofCWsforwastewatertreatmentandstrictwaterqualitystandardsisanevergrowingincentiveforthedevelopmentofbetterprocessdesigntools(Rousseauetal.,2004).Originally,workingwithsimpleregressionequations,mostresearchersanddesignersevolvedtowardstheuseofthewellknownfirst-orderk-C*model(KadlecandKnight,1996).Howeverthisblack-boxmodelisbasedononlytwoparameters,thefirst-orderdecayratek,andthebackgroundconcentration,C*,whichisanobviousoversimplificationofthecomplexwetlandprocesses.AshasbeenindicatedbyKadlec(2000)thefirst-ordermodelisinadequateforthedesignoftreatmentofwetlands.Morerecently,severaldynamic,compartmentalmodelsweredevelopedbyseveralresearcherssuchasMayoandBigambo(2005);NabizadehandMesdaghinia(2006);Brasiletal.(2007);Langergraber(2008);Giraldietal.(2010)andPimpanandJindal(2009).ThesestudieshaveshownpromisingresultsfortheCW*Correspondingauthor.E-mailaddress:yaqian.zhao@ucd.ie(Y.Q.Zhao).ContentslistsavailableatScienceDirectJournalofEnvironmentalManagementjournalhomepage:2010ElsevierLtd.Allrightsreserved.doi:10.1016/j.jenvman.2010.11.012JournalofEnvironmentalManagement92(2011)400e406processesforvariouswastewatertreatments.ThereforeattentionsandattemptshavebeenmadetoCWsmodelingandthispapertriestoreviewsuchdevelopments.2.CurrentstatusofCWsmodelsCWmodelsrangefromsimplesimulationmodelssuchasempirical,numericalandstatisticalmodelstomorecomplexprocess-basedmodel.ThedetailsofthecurrentstatusofCWsmodelingarepresentedbelow.2.1.Black-boxmodelcategory2.1.1.RegressionmodelsMajoritiesoftheinvestigationsontreatmentwetlandshavemainlybeenfocussedoninputeoutput(I/O)dataratherthanoninternalprocessdata.Anempiricalregressionanalysisisoftenperformedtodetermineifsignificantrelationshipsexistedbetweeninletandoutletconcentrationsofthewetlands.Asawhole,regressionequationsseemtobetheusefultoolsininter-pretingandapplyingtheseI/Odata(Rousseauetal.,2004).Stoneetal.(2002)usedtheregressionequation(Eq.(1))topredicttheoutletconce