Performanceofpilotscaleverticalflowconstructedwetl

Performanceofpilot-scalevertical-flowconstructedwetlandsinrespondingtovariationininfluentC/NratiosofsimulatedurbansewageYongJunZhaoa,b,BoLiua,c,WenGuangZhanga,YanOuyanga,ShuQingAna,b,*aStateKeyLaboratoryofPollutionControlandResourceReuse,NanjingUniversity,Nanjing210093,ChinabTheInstituteofWetlandEcology,SchoolofLifeScience,NanjingUniversity,Nanjing210093,ChinacDepartmentofEnvironmentalEngineering,CollegeofEnvironmentalScience,NanjingUniversity,Nanjing210093,ChinaarticleinfoArticlehistory:Received8June2009Receivedinrevisedform28September2009Accepted1October2009Availableonline23October2009Keywords:C/NratioCODremovalNitrogenremovalPhosphorusremovalLythrumsalicariaabstractTheperformanceresponseofplantedandtheunplantedwetlandstosimulatedwastewaterwithdifferentratiosofcarbontonitrogen(C/N)wasstudiedduringa9-monthperiodingreenhouseconditions.WithdifferentC/Nratiosforinfluentwater(C/Nratios2.5:1,5:1and10:1),averageremovalefficienciesfortheunplantedandtheplantedwetlandswereasfollows:COD(41–52%and59–68%),TN(24–48%and25–62%),TP(35–64%and59–71%)andTOC(22–37%and16–33%).AtC/N5:1,bothsystemsperformedmostefficientlyforremovalofCODandTP.However,highNremovalefficiencyonlyoccurredwhenC/Nratioranged2.5–5.BothwetlandsexhibitedgoodcapabilitiesoftotalorganiccarbonremovalatC/N10:1.Maybe,appropriatecontrolofthecarbonornitrogensourceconcentrationandC/Nratiointheinfluentcanachievetheoptimaleffectofnutrientsremoval.2009ElsevierLtd.Allrightsreserved.1.IntroductionConstructedwetlandshaveahighpotentialforwastewatertreatmentindevelopingcountriesduetotheirsimpleoperationandlowimplementationcosts(Konnerupetal.,2009).Theimple-mentationoflow-costtechnologysystemslikeconstructedwet-landscouldalsobeappropriatesolutionsfortreatmentofpollutedwastewatersinChina.Vertical-subsurfaceflowcon-structedwetlands(VFCWs)havebeenusedsuccessfullyinEuropeforthesewagetreatmentoverthelastfiveyears(Prochaskaetal.,2007).Theirsuccessisdependantongoodtreatmentperformancesobtainedfromhighchemicaloxygendemand(COD)of90%,nitrifi-cation(90%NHþ4—Nremoval)andlowoperationcosts(BrixandArias,2005;Tsihrintzisetal.,2007).However,phosphateremovalhasbeenfairlylow,typically20–30%(Luederitzetal.,2001).Bedcloggingisanoperationalproblemthatoftenoccursinsuchsys-tems(Langergraberetal.,2003).ThetreatmentperformanceofVFCWsdependsonavarietyofoperationalfactorsrelatingtothesystemitself,aswellasinfluentwaterquality.System-relatedfac-torsincludesubstratetypeandsize,maturityofthebedandcli-maticconditions(Merlinetal.,2002).Slagbedsenhancephosphorusremovaltolevelsofupto60%(Korkusuzetal.,2005).Consideringinfluentwaterquality,thereisverylimitedinformationoninfluentC/Nratiosandhowtheyaffecttreatmentperformance.However,influentwaterC/Nratioplaysacrucialroleinwastewatertreatments(SternerandElser,2002;Xiaetal.,2008).Oneconclusionwasthatmicro-organismsmustchangetheirC/N/Pstoichiometryasafunctionofgrowthrate.HighergrowthratesarecouplednotonlytohigherN/CandP/Cratios,butalsotolowerN/Pinmanyheterotrophicorganisms,includingbacteria(Elseretal.,2003;Makinoetal.,2003).Thekeytoefficientbiologicalwastewatertreatmentreliesonknowledgeoftheorgan-ismsinvolvedandhowtheyrespondtodifferentoperationalcon-ditions.Inaddition,thelowC/Nratiosintheinfluent,whichmaycauselowefficienciesofnitrogenandphosphateremoval.Inordertoaddresstheproblem,experimentswereconductedontreatingsimulatedmunicipalwastewaterwithdifferentC/NratiosbyVFCW.Inthestudy,weadjustedtheCOD,andtotalnitrogen(TN)con-centrations,andtheirweightedratiosinsimulateddomesticwastewater,whilemaintainingconstanttotalphosphorus(TP)0960-8524/$-seefrontmatter2009ElsevierLtd.Allrightsreserved.doi:10.1016/j.biortech.2009.10.002Abbreviations:COD,chemicaloxygendemand;TOC,totaloxygencontent;DO,dissolvedoxygen;TN,totalnitrogen;TP,totalphosphorus;Eh,redox-potential;VFCW,vertical-subsurfaceflowconstructedwetlands.*Correspondingauthor.Address:StateKeyLaboratoryofPollutionControlandResourceReuse,NanjingUniversity,Nanjing210093,China.Tel./fax:[phone].E-mailaddress:[e-mail](S.Q.An).BioresourceTechnology101(2010)1693–1700ContentslistsavailableatScienceDirectBioresourceTechnologyjournalhomepage:fi-ciencyofVFCWsduringonegrowingseason,andthustoidentifyoptimaloperationalparametersfornutrientremoval.Inparticular,wewishedtodeterminehowtreatmentperformancerespondedtodifferentC/Nratios,andthustoexplainandpredicttheperfor-manceofanoperatingwetlandssystem.2.Methods2.1.Characterizationofpilot-scalewetlandsThepilot-scalewetlandsweretwotypesofVFCWs,oneplantedwiththerhizomatousherbLythrumsalicaria,andtheotherun-planted(Fig.1).Thewetlandtanks,1.00mlong0.60mwide-0.80mhigh,weremadeofreinforcedconcrete,andwerefilledwithgravel(nominalmeandiameterofparticles,1.20cm)uptoadepthof0.20minthelowerlayerandwithslag(nominalmeanparticlediameter,1.50cm)uptoadepthof0.25mintheupperlayer.Theslaghadbeencleanedfivetimesinordertopreventthecreationofhighlyalkaline(highpH)conditions,that