Performance of integrated household constructed wetland for domestic wastewater treatment in rural

EcologicalEngineering37 (2011) 948–954

ContentslistsavailableatScienceDirect

Ecological

Engineering

journalhomepage:www.elsevier.com/locate/ecoleng

Performanceofintegratedhouseholdconstructedwetlandfordomestic

wastewatertreatmentinruralareas

ShubiaoWua,DavidAustinb,LinLiua,RenjieDongc,∗

aKeyLaboratoryofAgriculturalEngineeringinStructureandEnvironmentofMinistryofAgricultural,CollegeofWaterConservancy&CivilEngineering,ChinaAgriculturalUniversity,100083Beijing,PRChinabCH2MHILL,MendotaHeights,MN,USAcCollegeofEngineering,ChinaAgriculturalUniversity,100083Beijing,PRChina

articleinfo

Articlehistory:Received1May2010Receivedinrevisedform24January2011Accepted15February2011Available online 2 April 2011

Keywords:ConstructedwetlandRuralareasHouseholdwastewatertreatmentabstract

Asenvironmentallegislationhasbecomestricterinrecentyears,theissueofwastewatertreatmentinruralareashasbecomeanincreasingconcern.Choiceofthemostsuitableon-sitepurificationsystemsisbasedonthekeyissuesofaffordabilityandappropriatenessinChineseruralareas.Thispaperdescribesanintegratedhouseholdconstructedwetland(IHCW)systemplantedwithwillow(Salixbabylonica)totreathouseholddomesticwastewaterinruralvillagesinnorthernChina.TheprecastframestructureofIHCWisstrongandwaterproof.Itcanbemass-producedandinstalledperastandardsetofspecifications.TheIHCWhasachievedhighoverallremovalefficienciesforBOD5,TSS,NH4-N,andTP:96.0%,97.0%,88.4%and87.8%,respectively.A0.4mbiomasslayercoveronthesystemprovidedsignificantsystemthermalinsulation,maintaininghightreatmentperformanceinfreezingwinterconditions.Thesystemiscosteffectiveanddoesnotneedanyoperationalenergyinputs,demonstratingitsfeasibilityforsingle-familyuseindevelopingcountries.© 2011 Elsevier B.V. All rights reserved.

1.Introduction

Domesticwastewatertreatmentinruralareasisessentialto

preventpollutionofaquaticenvironments,whichhasbeenof

increasingconcernforbothresearchersandgovernmentofficials

(Ichinarietal.,2008).Theseconcernsareapreludetotoughing

environmentallegislation.

EstimatesfromtheWorldHealthOrganization(WHO)andthe

WaterSupplyandSanitationCollaborativeCouncilindicatethat

<18%ofruralpopulationshaveaccesstosanitationservicesin

developingcountries(Massoudetal.,2009).Infact,theamountof

domesticwastewatertreatedinChinaisjust11%forcountytowns

and<1%forruralvillages(Panetal.,2007).Toaddressthissitu-

ation,in2005,theChinesegovernmentputforwardthestrategic

plan“NewSocialistCountrysideBuilding”.Methodsofimproving

thelivingenvironmentanddealingwithdomesticwastewaterin

ruralareashavebeenanurgentconcernoftheChinaStateCouncil

andStateEnvironmentProtectionAdministration.

Householdsinruralareasthatdonothavepublicsewersmust

dependonon-sitetreatmentsystemstomanagetheirwastewater.

Manyon-sitewastewatertreatmenttechnologies,suchasseptic

∗Correspondingauthor.E-mailaddress:wsb4660017@126.com(R.Dong).tanks,drain-fieldsystems,lagoons,aerobicbiologicaltreatment

units,membranebioreactors(MBRs)andconstructedwetlandsare

available(Nakajimaetal.,1999;Abegglenetal.,2008).A“Most

AppropriateTechnology”istheonethatiseconomicallyafford-

able,environmentallysustainable,andsociallyacceptable.On-site

treatmentsystemsoftendonotmeettheserequirements.High

totalsuspendedsolids(TSS),biochemicaloxygendemand(BOD),

totalfecalcoliforms,totalnitrogen(TN),andtotalphosphorus(TP)

makeseptictankeffluentunsuitabledischargetowaterbodies

(Carrolletal.,2006).Traditionalleach-fieldsystemsareproneto

failureinareaswithimpermeable,heavyclaysoils,andalsopro-

videinadequatetreatmentinareaswithhighlypermeablesoils

andhighwatertables.Lagoonstendtobeunpleasantfromanaes-

theticperspectiveandbecauseofodorproduction(Burkhardetal.,

2000;Garcíaetal.,2001).Aerobicbiologicaltreatmentunitand

membranebioreactors(MBRs)effectivelyremovepollutants,but

havehighcapital,operationsandmaintenancecoststhatarenot

affordableindevelopingcountries(Nakajimaetal.,1999;Daude

andStephenson,2004;Ichinarietal.,2008;Renetal.,2010).Con-

structedwetlandshavehighpollutantremovalefficiency,aswell

aslowcostandsimpleoperation(BrixandArias,2005;Siracusa

andLaRosa,2006),butcanbelimitedbyseasonalchangesin

treatmentcapacityandlargearearequirements(Brix,1994).Itis

apparentthatasuccessfulandsustainablesystementailsawide

rangeofcriteriaincludingenvironmental,technicalandsocialcul-

0925-8574/$–seefrontmatter© 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.ecoleng.2011.02.002S.Wuetal./EcologicalEngineering37 (2011) 948–954949

Fig.1.Schematicdiagramoftheintegratedhouseholdconstructedwetlandsystem(thedotedredlineshowsthewaterflowpath).(Forinterpretationofthereferencestocolorinthisfigurelegend,thereaderisreferredtothewebversionofthearticle.)

turalfactors.Thatistheunderlyingreasonsomecurrentlyavailable

practicesadoptedfromothercountriescanbeincompatiblewith

localrequirements,limitations,andconditions(Massoudetal.,

2009;Renetal.,2010).Itisthereforeessentialtoconductresearch

intoanalternativedisposalsystembasedonlocalrequirementsand

conditionsforthetreatmentofwastewaterfromatypicalsingle

familyinruralChina.

Thispaperdescribesanewon-sitewastewatertreatmentsys-

tem(IntegratedHouseholdConstructedWetland,IHCW)forrural

householdwastewatertreatment.Thesystemconsistsofatwo-

stagesedimentationtankandavertical-flow,constructedwetland

bed.Theprecaststructureisstrongandwaterproof.Modularcon-

structionallowsforinstallationwithunskilledlabor.Itisexpected

thatthesystemmayovercomethelocallimitationsofsoilcon-

ditionsandunskilledconstruction.Additionally,theinsulating

biomasslayeratthewetlandbedsurfaceallowsthesystemto

runnormallyinfreezingtemperatures.Thisconceptappearsto

offeradvantagesforhouseholdwastewatertreatmentindevelop-

ingcountries,wherereallylow-cost,convenientconstructionand

operationalsimplicityareessential.

2.Materialsandmethods

Theexperimenttookplaceinthebackyardofaruralfamilyin

ChangPing,Beijing,China.Itwasaninsulated,at-grade,vertical-

flowmodeltoavoiddamagefromlowtemperaturesinwinter

(Fig.1).Thesystemconsistedofatwo-stagesedimentationtank

andaverticalflowconstructedwetlandbedsection.Theframe

structurewasprecastwithmagnesiacementandfiberglassfabric

whichisstrongandwaterproof.Inplanviewthestructureisellipti-

calwiththebottomsmallerthanthetoptofacilitatetransportation.

Itcanbedirectlyinstalledafterexcavation.Thetwo-stagesedi-

mentationtankconsistsoftwosegmentswithequalempty-bed

volumeforeachsegmentof0.5m3.Theemptyvolumeofthewet-

landbedsectionis1.2m3(area×depth:1.2m2×1.0m).Asteel

sievewasinstalledintheinletbasintopreventlargesolids(such

asvegetableleavesandfishscalesfromthekitchen)fromflow-

ingintothetank.Wastewaterflowsintothefirstsegmentfrom

theinletbasinandthenintothesecondsegmentviaafloating

valveinstalledinthefirstsegmenttoallowintermittentsystemfeeding.Inordertomaintainnormaloperationduringthewinter

period,0.4mofsawdustinsultsthebed.Wastewaterflowsfromthe

sedimentationtankdownwardsthrougha60mmdiameterperfo-

ratedplasticpipewith5mmholeslocatedatthetopofthesand

layerandthentricklesthroughthewetlandbed.Theeffluentflows

intothebottomgravellayerandthenthroughthedewateredalum

sludgeplacedintheoutlet,andfinallyflowsintotheground.The

dewateredalumsludgeisabyproductfromdrinkingwatertreat-

mentplantsandhasbeenreportedtoenhancePremovalduetoits

highcontentofamorphousaluminum(BabatundeandZhao,2007,

2009;Razalietal.,2007).

Thebedmediafromthebottomtothetoparewashedgravel,

peagravelandsandwhichwasmodifiedaccordingtothestan-

darddesigncriteria(BrixandArias,2005):a15cmlayerofwashed

gravelwithparticlesizeof10–30mm,15cmofwashedpeagravel

withparticlesizeof5–12mm,and90cmofwashedsand.The

effectivesizeofthewashedsandis0.45–1mmwithauniformity

coefficientof3.8.Seventyfivekilogramsofwasheddewateredalum

sludgederivedfromdrinkingwatertreatmentplantwithparticle

sizeof0.5–1mmwasputintheoutletofthesystem.Themedium

surroundingthedistributionpipenetworkwas10cmofgravelwith

particlesizeof10–30mm.

Awillow(Salixbabylonica)withatrunkdiameterof40mmwas

plantedintheverticalflowwetlandbedsection.Thewillowwas

selectedasthewetlandplantforseveralreasons.InChinapeople

wouldpreferatreeintheirbackyardratherthanwetlandplants.

Theexperienceofsomeconstructedwetlandsystemswithwillows

inDemarkhassuccessfullyprovidedashowcaseofgoodperfor-

manceinnutrientsandheavymetalsremoval(Hasselgren,1998;

SanderandEricsson,1998),probablyduetothewell-developed

rootsystemwillowsproduced.Willowsarealsocoldhardyinthe

harshclimaticconditionsofnorthernChina.

ThesystemwasplantedandthenseededinNovember2007.

SamplingevensoccurredfromMarch2008toFebruary2009.Dur-

ingtheexperimentoperation,householdwastewaterinfluentwas

comprisedofkitchenandlaundryeffluents.Thehydraulicloading

ratewasabout0.12md−1.Watersamplesofapproximately200ml

werecollectedfromtheinfluent,sedimentationtank(secondseg-

ment),andeffluent(Fig.1)at7–10daysintervalstoevaluatethe

treatmentperformances.Wastewaterparametersofbiochemical

oxygendemand(BOD5,5210B.5-dayBODtest),totalsuspended

solids(TSS,2540D.totalsuspendedsolidsdriedat103–105◦C),

ammonia-nitrogen(NH4-N,4500G.automatedphenatemethod),

andtotalphosphorus(TP,4500F.automatedascorbicacidreduc-

tionmethod)weremeasuredonthesamedayofcollectioninthe

KeyLaboratoryofAgriculturalEngineeringinStructureandEnvi-

ronmentofChinaMinistryofAgricultureaccordingtotheStandard

Methods(AWWA,1999).ThepHandDOweremeasuredinsitufor

eachsampleusingaportablemeter(Orion-5-Star,510M-62).For

eachoftheparameters,sampleswerecollectedandanalyzedin

triplicate.Meanandstandarddeviationvalueswerereported.The

dailyairtemperatureofmeteorologicaldataintermsofmaximum

andminimumwasprovidedbytheBeijingMeteorologicalBureau,

Beijing,China.Thetemperatureoftheverticalconstructedwetland

bedwasdeterminedbyatemperaturesensor(Pt1000,Yonghua,

China)installedinthemiddledepthofthebed(Fig.1).

Face-to-facequestionnaireswereconductedamong158home-

respondentstoevaluatefarmers’willingnesstopayfortreatment

andthepotentialapplicationoftheintegratedhouseholdcon-

structedwetlandinruralvillages.

3.Results

Thewastewaterusedforexperimentwasgeneratedinasingle

household,excludingtoiletwastewater.Averageconcentrations