Removal of nutrients from combined sewer overflows and lake water in a verticalflow constructed.docx
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Removal of nutrients from combined sewer overflows and lake water in a verticalflow constructed.docx
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Removalofnutrientsfromcombinedseweroverflowsandlakewaterinaverticalflowconstructed
本科毕业设计
外文文献及译文
文献、资料题目:
Removalofnutrientsfromcombinedseweroverflowsandlakewaterinavertical-flowconstructedwetlandsystem
文献、资料来源:
期刊
文献、资料发表(出版)日期:
院(部):
市政与环境工程学院
专业:
给水排水工程
班级:
姓名:
学号:
指导教师:
翻译日期:
2013.3.24
外文文献:
Removalofnutrientsfromcombinedseweroverflowsandlakewaterinavertical-flowconstructedwetlandsystem
L.GervinandH.Brix
Abstract
LakeUtterslevissituatedinadenselybuilt-upareaofCopenhagen,andisheavilyeutrophicatedfromcombinedseweroverflows.Atthesametimethelakesuffersfromlackofwater.Therefore,a5,000m2verticalflowwetlandsystemwasconstructedin1998toreducethephosphorusdischargefromcombinedseweroverflowswithoutreducingthewatersupplytothelake.Duringdryperiodstheconstructedwetlandisusedtoremovephosphorusfromthelakewater.Thesystemisdesignedasa90mdiametercircularbedwithabeddepthofc.2m.Thesystemisisolatedfromthesurroundingsbyapolyethylenemembrane.Thebedmediumconsistsofamixtureofgravelandcrushedmarble,whichhasahighbindingcapacityforphosphorus.Thebedislocatedwithinthenaturallittoralzoneofthelakeandisplantedwithcommonreed(Phragmitesaustralis).Theconstructedwetlandisintermittentlyloadedwithcombinedseweroverflowwaterorlakewaterand,afterpercolationthroughthebedmedium,thewateriscollectedinanetworkofdrainagepipesatthebottomofthebedandpumpedtothelake.Thefullyautomatedloadingcycleresultsinalternatingwetanddryperiods.Duringtheinitialtwoyearsofoperation,thephosphorusremovalforcombinedseweroverflowshasbeenconsistentlyhigh(94–99%ofinflowconcentrations).Whenloadedwithlakewater,thephosphorusremovalhasbeenhighduringsummer(71–97%)andlowerduringwinter(53–75%)partlybecauseoflowerinletconcentrations.Effluentphosphorusconcentrationsareconsistentlylow(0.03–0.04mg/L).Ammoniumnitrogenisnitrifiedintheconstructedwetland,andtotalsuspendedsolidsandCODaregenerallyreducedtoconcentrationsbelow5mg/Land25mg/L,respectively.Thestudydocumentsthatasubsurfaceflowconstructedwetlandsystemcanbedesignedandoperatedtoeffectivelyremovephosphorusandotherpollutantsfromcombinedseweroverflowsandeutrophicatedlakewater.
Keywords:
Combinedseweroverflow;constructedwetland;nitrogen;phosphorus;stormwater;urbanrunoff;vertical-flowsystem;watertreatment
Introduction
Lakeslocatedindenselybuilt-upareashaveahighrecreationalvalueforthepublic.However,becauseoftheintensiveurbandevelopmentandhumanactivitiesinthecatchmentofthelakes,thewaterqualityisoftenpoorandreducestherecreationalvalues.Dischargeofuncontrolledurbanstormwaterandcombinedseweroverflowsmaybemajorcontributorstothedeteriorationofthewaterquality.Stormwaterrunofforiginatesasrunofffromparkinglots,roads,roofsandotherimpervioussurfaces,andasrunoffacrossbareorvegetatedsoils.Combinedseweroverflowsoccurduringraineventswhenlargeamountsofrainwaterareaddedtothenormaldomesticflowsoftheseweragesystems.Upgradingandextendingtheseweragesysteminthecatchmentofthelakesmayreducethesesourcesofpollution,butoftenthiswillalsoleadtoanundesirablediversionofamajorpartofthefreshwatersourceforthelakes.Anotheroptionistocleantherunoffwaterandthecombinedseweroverflowsbeforedischargetothelake.
LakeUtterslevisanurbanmarshsystemlocatedinadenselybuilt-upareaabout10kmnorthwestofthecitycentreofCopenhagen.Themarshcovers91haandhasameanwaterdepthofc.1metre.Themarshhasatpresentnonaturalinflow,butwaterispumpedtothelakesthroughachannelatthewestendofthemarsh.Inaddition,themarshreceivesurbanrunoffandcombinedseweroverflows.Theresidencetimeofthewaterinthelakesisthreetothirteenmonthsduringsummer.Until1970thelakesinUtterslevmarshreceivedlargedischargesofuntreatedandpoorlytreatedwastewaterand,inspiteofdiversionandtreatmentofthesewagewater,thelakesareheavilyeutrophicated.Theyearlymeanphosphorusconcentrationofthelakewateris0.3–0.4mg/L,andbecauseofthelargepoolofnutrientsaccumulatedinthesediments,releaseofphosphorusinthewarmsummermonthsperiodicallyraisestheconcentrationsofphosphorusinthelakewatertomorethan1mg/L(MunicipalityofCopenhagen,2000).Hence,thereisnosubmergedaquaticvegetationinthelake,andwaterqualityisgenerallypoorbecauseofalgalblooms.Themarshishoweverasignificanthabitatforbirdsandotherfauna,andhasgreatrecreationalvalueforthepublic.Therefore,duringrecentdecadeslargeinvestmentshavebeenmadeinordertoimprovetheenvironmentalconditionsinthemarsh.
Constructedwetlandsystemshavebeensuccessfullyestablishedtotreatcombinedseweroverflowsandurbanstormwater(e.g.Shutesetal.,1997;Greenetal.,1999;Scholesetal.,1999).In1998theMunicipalityofCopenhagendevelopedandconstructedawetlandsystemtotreatthecombinedseweroverflowbeforedischargeintothemarsh(SeehuusenandGervin,1999).Thiswasdoneinordertoreducetheloadingofphosphorusinparticulartothemarsh,andatthesametimeretainthesupplyofwatertothemarsh.Besidestreatingcombinedseweroverflows,theconstructedwetlandisusedtocleanlakewaterin“dry”periodswhentherearenoseweroverflows.Thispaperdescribesthesystemdesignandoperationalschemesandpresentsresultsfromtheinitialtwoyearsofoperation.
Locationanddesignoftheconstructedwetland
Theconstructedwetlandislocatedinthenaturallittoralzoneofoneofthelakesinanexistingreedswamp(Figure1).Thesystemisdesignedasa90mdiametercircularbedpartlyburiedintheswampandisseparatedfromtherestoftheswampbyapolyethylenemembrane(Figure2).Themembraneisplaced3mbeneaththewaterlevelofthelakeontheunderlyingclaylayer.Thetwometredeepbedsubstrateconsistsofamixtureofgravelandcrushedmarble,whichhasahighbindingcapacityforphosphorus(Brixetal.,2001).Thesurfacelevelofthebedmediumislocatedonemetrebeneaththewaterlevelofthelake.Theplantissurroundedbyadikeofearth,andisplantedwithreeds(Phragmitesaustralis).Thesurfaceareaoftheplantis5,000m2,andthestoragecapacityforwaterinthesystem,includingthevoidvolumeofthe
Figure1Locationofthecircularconstructedwetlandsystem(CW)inUtterslevmarsh
bedmedium,is6,500m3.Theinlet-pipesareburiedinadikeleadingtothecentreoftheplant,fromwheretheinfluentwaterisdistributedoverthesurfaceofthebed(Figure3).Thesystemisintermittentlyloadedwithcombinedseweroverflowwaterorlakewater,andafterpercolationthroughthebedmedium,thewateriscollectedinanetworkofdrainagepipesatthebottomofthebedandpumpedtothelake.
Figure2Cross-sectionthroughthecircularconstructedwetlandsystematUtterslevmarsh
Aburiedin-lineretentionbasinbuiltintotheseweragesystemislocatedimmediatelyupstreamoftheconstructedwetlandsystem.Thebasinwithholdsthe“firstflush”ofthecombinedseweroverflow,andthereforethewatergoingintothewetlandduringoverfloweventsisratherdilute.Duringperiodswithnooverflowevents,thesystemisusedtocleanlakewater.Thefullyautomatedloadingcyclesresultinalternatingwetanddryperiods.
Figure3PhotographoftheconstructedwetlandsystematUtterslevmarshshowingaboardwalkleadingtothecenterofthecircularbed
Severalbuilt-inattributesofthesystemcontributetoenhancethenutrientremovalperformance.
Thebedmediumisrelativelydeep(2m)andcontainscrushedmarble,whichhasahighbindingcapacityforphosphorus(Brixetal.,2001).Thevertical-flowregimensecuresagoodcontactbetweenthewaterandbedmedium,andtheintermittentloadingcreatesalternatingwetanddryperiodswhichincreaseoxidationoforganiccompoundsandnitrificationinthebedmedium.
Theroutineoperationofthesystemisautomatedviadataacquisitionandrealtimecontrol.Thecontrolisbasedonflowtransmittersmeasuringinfluentandeffluentflowrates,andleveltransmittersplacedintheretentionbasinandintheconstructedwetlanditself.Furthermore,on-linemonitoringequipmentisinstalledinthesystemtomeasureoxygen,temperatureandpHintheinletandtheoutletwater,indifferentdepthsofthefreewateronthesurfaceofthebedduringloadingperiods,aswellasindifferentdepthswithinthebedmedium.Automaticsamplersareinstalledattheinletandoutletofthebedtakingsamplesproportionaltovolumeflow.
Treatmentperformanceofthesystem
Theinitialperiodofoperationhasbeenarunning-inperiod,wherethefocushasbeentostudytheeffectsofresidencetimeonremovalperformance.IntheperiodfromOctober1998toJanuary1999onlylakewaterwithlowcontentsofnutrientsweretreatedinthesystemastherewerenooverflowsfromthesewersystemuntilJune1999.IntheperiodfromOctober1998tothefirstofJanuary2000atotalof125,000m3ofwaterweretreatedinthesystem(115,000m3in1999).Theinflowsconsistedofc.50loadingsoflakewater(42loadingsin1999),and16loadingsofseweroverflows.Theperformancewhentreatinglakewaterwastestedbyanalysisof24in-andoutletsamples.Theperformancewhentreatingseweroverflowswastestedbyanalysisof12inletand16outletsamples.Attwooftheoverfloweventssamplesweretakenoftheoutletwaterafter3,5
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