Effectsofloadingrestingperiodtemperatureporousmedi

ChemicalEngineeringJournal181–182(2012)416–430ContentslistsavailableatSciVerseScienceDirectChemicalEngineeringJournaljournalhomepage:flowconstructedwetlandsAlexandrosI.Stefanakis,VassiliosA.Tsihrintzis∗LaboratoryofEcologicalEngineeringandTechnology,DepartmentofEnvironmentalEngineering,SchoolofEngineering,DemocritusUniversityofThrace,67100Xanthi,GreecearticleinfoArticlehistory:Received29July2011Receivedinrevisedform29November2011Accepted29November2011Keywords:ConstructedwetlandsVerticalflowLoadingrateRestingperiodTemperaturePorousmediaVegetationAerationOrganicmatterNitrogenPhosphorusabstractTenpilot-scale,cylindrical,verticalflowconstructedwetlands(area0.57m2)wereconstructedandoper-atedcontinuouslyforthreeyearsinparallelexperiments,treatingsyntheticwastewater,simulatingthefirsttreatmentstageoffull-scalesystems.Thewetlandunitswereplantedwithtwoplantspecies(i.e.,commonreedsandcattails),haddifferentporousmediamaterialcomposition(i.e.,carbonate,igneous,zeoliteandbauxite)andthreedifferenttotalsubstratethicknessesandgradations.Threeloading/restingscheduleswereused.Waterqualitysampleswerecollectedattheinletandtheoutletofeachunit,andwereanalyzedinthelaboratoryforthedeterminationofvariouspollutants.TheVFCWunitswerequiteefficientinorganicmatter(BOD5andCOD)andnitrogen(TKNandNH4+-N)removal,withmeanremovalefficienciesexceeding78%and58%,respectively.Meanphosphorus(TPandOP)removalwaslower(37%).Theunitswerefoundtoprovidesignificantpollutantremovalunderhighorganicloads,upto200gCOD/m2d.Thepresenceofreedsandaerationtubeswasfoundtoimprovetheperformance,whileplantspeciesdidnotaffectefficiency.Theuseofspecialmaterials,aimingatenhancingtheadsorptionofdifferentconstituents,didnotimprovethewetlandefficiency,probablyduetolimitedcontacttimebetweenmaterialandwastewater,andisnotrecommended.©2011ElsevierB.V.Allrightsreserved.1.IntroductionandbackgroundTheuseofnaturalwetlandsfortreatmentofwastewaterhasbeenpracticedforseveraldecadesinthepast[1].Sincethe1950s,thewetlandtechnologyemergedandtheuseofcontrolledwetlandenvironmentsforwastewatertreatmentwasdeveloped.Constructedwetlands(CWs)appearnowadaysasareliable,effec-tiveandfeasiblesolutioninthefieldofwastewatertreatment[2,3].Theycanbeclassifiedbythetypeofplants(freefloating,rootedemergentandsubmergedsystems)orbythetypeofflow(horizon-talorvertical)[4].TheuseofVerticalFlowCW(VFCWs)systemsinEuropebecameverypopularinthe1990s.Theadoptionofstrictdisposallim-itsfornitrogenfavoredtheapplicationofVFCWscomparedtohorizontalsystems[1],duetotheirenhancedabilitytooxidizeammonianitrogen.InVFCWsystems,thewastewaterfillsperiodi-callythewetlandmatrixandthendrainscompletelybygravity.Thiswayoffeedingprovideshighlevelsofoxygentransferwithinthesubstrate,whichallowsforgoodtreatmentperformance,especially∗Correspondingauthor.Tel.:[phone];fax:[phone];mobile:[phone].E-mailaddresses:[e-mail],[e-mail](V.A.Tsihrintzis),[e-mail](A.I.Stefanakis).fororganicmatterandnitrogen[5,6],asalsopreventssubstrateclogging.Phosphorusremovaliscomparativelylow[5,7,8].ThehighammoniaoxidizingabilityofVFsystemsalsopromotedtheiruseintreatmentofhighammoniawastewater,suchaslandfillleachates[9]andfoodprocessing[10].AtypicallayoutofaVFCWsystemconsistsofasedimentationtankforwastewaterpre-treatment,theVFCWbedsandaneffluentditch[5].Theuseofanorganicsubstrateatlownitrogenconcen-trationswasfoundtosignificantlyenhancedenitrification[11].Furthermore,denitrificationmayoccurinVFCWsoperatingunderheavyload(i.e.,whenorganiccarbonisavailable),andalso,theremayexistanoxicmicro-zonesinaVFCWwheredenitrificationmaytakeplace;nevertheless,thisprocesshasbeengenerallyreportedtobelimitedinVFCWs[1,12].Therefore,thedesignofhybridsys-tems(combinationofverticalandhorizontalflowsystems)hasbeenproposedtoexploittheanoxicareaswithinthehorizontalbedfordenitrification[6,13–15].Recirculationoftreatedeffluenthasalsobeenevaluatedasapossibledenitrificationenhancementconfiguration[16,17].ApromisingapplicationofVFCWsisalsoinactivatedsludgedewateringandmineralization[18–21].InmanycountriesacrossEurope,therehavebeenproposeddifferentdesignguidelines,varyinginsurfaceareafrom1to5m2/pe[22].ThetreatmenteffectivenessofaVFCWdependsonvariousdesignandoperationcharacteristics.Parametersforwet-landdesignincludethehydraulicload,theplantspecies,the1385-8947/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.doi:10.1016/j.cej.2011.11.108A.I.Stefanakis,V.A.Tsihrintzis/ChemicalEngineeringJournal181–182(2012)416–430417substratematerialandthewastewatersourceandquality[6].Asat-isfactorytreatmentiscloseconnectedtoanappropriatehydraulicloadandwastewatersupply.Furthermore,thephysicochemicalpropertiesoftheselectedsubstratematerialcouldberelatedtosystemperformance,especiallyregardingphosphorusandammo-niaremoval.Likewise,thegoodaerationofthebed(presenceofaerationtubes,intermittentloadingforaerobicconditionre-establishmentorforcedaeration)mayalsobeimporta