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BiosystemsEngineering(2004)87(1),109–118doi:10.1016/j.biosystemseng.2003.10.005Availableonlineat}RuralDevelopmentConstructedWetlandsasaSustainableSolutionforWastewaterTreatmentinSmallVillagesM.L.Solano1;P.Soriano1;M.P.Ciria21BiomassProject,RenewableEnergyDepartment,CIEMAT,AvdaComplutense22,Madrid28040,Spain;e-mailofcorrespondingauthor:ml.solano@ciemat.es2CIEMAT-CEDERKm206CarreteraN-111Madrid-Soria,42290Lubia,Soria,Spain;e-mail:pilar.ciria@ciemat.es(Received28May2003;acceptedinrevisedform7October2003;publishedonline20November2003)Withtheaimofsolvingthewastewatertreatmentprobleminsmallvillages,treatmentperformanceofapilot-scalesubsurface-flowconstructedwetland(SFW)wasevaluatedforremovalefficiencyofbiochemicaloxygendemand(BOD),chemicaloxygendemand(COD),totalsuspendedsolids(TSS),totalandfaecalcoliformandfaecalstreptococcibacteriafromrawmunicipalwastewater.Studiesofthecompositionandthermalbehaviouroftheharvestedbiomasswereachievedinordertoassesstheirpossibleutilisationasafuel.Twodifferenthydraulicapplicationrates(150,and75mmday1)andtwomacrophytes,cattail(Typhasp.)andreed(Phragmitessp.),wereassayed.HighlevelsofBOD,CODandTSSremovalforalltreatmentswereobtained.Thebestremovalswereobtainedinthosebedswiththelowesthydraulicapplicationrate.Withregardtothetypeofplant,nosignificantdifferenceswerefoundbetweencattailandreedperformance;however,cattailsshowedtobebyfar(almostafactorof2)thegreatestproducerofbiomass(22t[d.m.]ha1).Bothcattailsandreedspresentedhighheatingvalues(17–20MJkg1).Accordingtotheseresults,itcanbeconcludedthatthewetlandsystemutilisedinthisresearchcouldbeasuitablesolutionforrawwastewaterasastand-alonetreatment,althoughapreviouspre-treatmentinordertoremovegrit,heavysolidsandfloatablematerialswouldbenecessary.Besides,theobtainedbiomasscouldbeutilisedasfuelinasmallboilerfordomesticuses.#2003SilsoeResearchInstitute.AllrightsreservedPublishedbyElsevierLtd1.IntroductionConventionalwastewatertreatmentplantsinvolvelargecapitalinvestmentsandoperatingcosts,andforthatreasonthesesystemsarenotagoodsolutionforsmallvillagesthatcannotaffordsuchexpensivecon-ventionaltreatmentsystems.Constructedwetlandsaregainingimportanceasaneffectiveandlow-costalternativefortreatmentofsepticeffluentsinsmallvillages.Suchsystemshavecertainadvantagesovertheconventionaltreatmentsystems:theycanbeestablishedinthesameplaceaswherethewastewaterisproduced;theycanbemaintainedbyrelativelyuntrainedpersonnel;theyhaverelativelylower-energyrequirementsandarelow-costsystems.Thesewetlandsareusuallyutilisedassecondaryandevenastertiarytreatment(Greenetal.,1996;Stoberetal.,1997;Billoreetal.,1999;Nerallaetal.,1998).Alternatively,constructedwetlandscanbeusedforprimarytreatment,wherethewetlandistheonlytypeoftreatmentusedandinthiscase,toxiceffectsontheaquaticplantsduetothehighorganicloadingoftheinfluentshasbeenreported(Gersbergetal.,1986;Haynes&Goh,1978).Theaimofthisworkhasbeentostudythefeasibilityofaconstructedwetlandtotreatrawwastewater,sinceinordertobeaneffectivedisposalsysteminsmallpopulationcentresthewetlandneedstobekeptsimple,asa‘stand-alone’plant.Ifasecondaryor,worseyet,atertiarytreatmentisneeded,itwillrenderthesystemasanunrealisticalternative.Studiesofthecompositionoftheharvestedbiomasshavebeenachievedinordertoassesstheirpossibleutilisationasafuelindomesticboilers.Forthispurpose,apilot-scalesubsurface-flowartifi-cialwetland(SFW)hasbeenconstructed.ThispaperARTICLEINPRESS1537-5110/$30.00109#2003SilsoeResearchInstitute.AllrightsreservedPublishedbyElsevierLtddescribesinvestigationsusingthiswetland,whichquantitativelyassesstheroleoftwomacrophytes,cattail(Typhasp.)andreed(Phragmitessp.),intheremovalofbiochemicaloxygendemand(BOD),chemicaloxygendemand(COD),totalsuspendedsolids(TSS),andpathogenicbacteriafromrawmunicipalwastewaters.Thepaperpresentsdatafrom2yrofoperation.2.Materialsandmethods2.1.DescriptionoftheexperimentalsiteTheconstructedwetlandwasbuiltneartheSoriasewagetreatmentplant(418360Nlatitude,28300Wlong-itude,andmeanheightabovesealevel1010m),situatedinthenorth-centralpartofSpain.TheclimateoftheareaisMediterraneansemi-aridwithanaverageannualrainfallofabout480mm.Theannualmeanmaximumandminimumtemperatureswere22and58C,respec-tively.Thewetlandconsistedoftwoserieswithdifferenthydraulicapplicationrates(HAR),150and75mmday1(retentiontimesof15and3days,respectively).Eachseriesconsistedoftwobeds,oneplantedwithcattailandtheotherplantedwithreed.ThedistributionofthebedsisshowninTable1.Eachwetlandbedwas40m2,with05–1cmdiametergravelasthesupportingmediumandalengthtowidthratioof10:1.Thedepthofeachbedwas1mandthegraveldepth040m(Fig.1).Animpermeableplasticlinerwasplacedatthebottomofeachbedtopreventground-watercontamination.Aninletandoutletzone,each1m,consistingoflargestones(5–10cm),wasusedtoeliminatetheeffectsoftheinletandoutlet.Eachbedhadapolyvinylchloride(PVC)inletpipeatitstop,endingwithhorizontaldrainagepipeof15mlongand50mmdiameter.Theinfluentintoeachbedwascontrolledmanuallyeverydaybymeasuringtheflowrateandadjustingthevalvetomaintainacontinuousdailyflowrat