small scale wastewater treatment for single houses

7/21/2019 Small Scale wastewater treatment for single houses

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KUNGLIGA TEKNISKA HGSKOLAN

Small scale wastewatertreatment in single houses

ValerieSeh,PhilipSunesson,LindeSedell,EmmanouilMilathianakis

20150228


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Tableofcontent

Introduction ..................................................................................................................................... 2

Purpose & methodology ................................................................................................................. 2

Background ..................................................................................................................................... 2

Domestic wastewater .................................................................................................................. 2

Wastewater treatment ................................................................................................................. 3

Parameters for consideration ...................................................................................................... 3

Methods .......................................................................................................................................... 4

Septic Tank & drain field System ................................................................................................ 4

Background .............................................................................................................................. 4

Construction ............................................................................................................................. 4

Treatment and operation ......................................................................................................... 5

Cost .......................................................................................................................................... 6

Maintenance ............................................................................................................................ 6

Miniature water treatment plant .................................................................................................. 6

Background .............................................................................................................................. 6

Construction ............................................................................................................................. 7

Treatment and operation ......................................................................................................... 8

Cost .......................................................................................................................................... 9

Maintenance ............................................................................................................................ 9

Constructed Wetlands ................................................................................................................. 9

Background .............................................................................................................................. 9

Construction ........................................................................................................................... 10

Treatment and operation ....................................................................................................... 10

Cost ........................................................................................................................................ 10

Maintenance .......................................................................................................................... 10

Case study .................................................................................................................................... 11

Location ..................................................................................................................................... 11

Geology ..................................................................................................................................... 11

Protection level .......................................................................................................................... 12

Discussion and conclusion ........................................................................................................... 13

References .................................................................................................................................... 14


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IntroductionWaterisanessentialelementthathumansuseintheirdailylivesandthegenerationofwastewateris

inevitable.Wastewatercontainspathogens,nutrientsandevenchemicalswhichcanbeahazardtobothenvironmentandhumanhealthifitisnottreatedproperlybeforeitisbeingdisposedof.Inmost

developedcountries,wastewatertreatmentplantsandtechnologiesarereadilyavailabletotreat

wastewaterwithinthecities.However,inthecaseofruralareas,theremaybedifficultiestothe

accessibilityandavailabilityofwastewatertreatmenttechnologies.Thisisthecasewhenruralareasare

sparselypopulated,locatedgeographicallyfurtherawayandmayfaceproblemsinaffordability.Assuch,

itisimportanttolookforalternativetechnologiesthatenabletheonsitetreatmentofwastewater

beforeitisdisposedbacktothenature.Thetechnologiesshouldbeinbeneficialtothehealthandthe

environmentofthoselivingintheruralareas.

Purpose & methodologyThescopeofthisprojectistoidentifyappropriatewastewatertreatmenttechnologiesforsingle

householdsthatdonthavetheabilityorforotherreasonschoosetonotgetconnectedtoacentralora

municipalsewagesystem.Theaimistousetheidentifiedmethodstofindagoodsolutionfora

householdsituatedintheareaofstudypresentedinthereport.

Firstathoroughliteraturestudywasconductedtogetagoodoverviewofthedifferentwastewater

treatmenttechniquesthatareusedtoday.Aftertheliteraturereview,fourwastewatertreatment

methodswereidentifiedforfurtherresearch.Eachmethodwasindependentlyexaminedandanalyzed

regardingthebackgroundofthemethod,constructioncharacteristics,treatmentandoperation

proceduresandfinallycostsandmaintenance.

Afterthatthebestmethodfortheareaofthecasestudywaschosendependingontheefficiencyofthe

methodandtherequirementsforthearea.

BackgroundWastewateriswaterthathasbeenaffectedinqualitybyanthropogenicuse. Thewaterproducedin

householdsiscalleddomestic,mostwastewaterishoweverproducedbyindustries.

Domestic wastewaterDomesticwastewateriswastewaterproducedbyasinglehouseholdanddividedintotwocategories.

Firstly,thegraywaterwhichcomesfromshowers,baths,washingmachines,dishwashersandsecondly

theblackwaterwhichcomesfromtoiletsandkitchensinks.Domesticwastewaterismainlycomprised

ofwater(morethan95%)andsmallconcentrationsofsuspendedanddissolvedorganicsolidsas

carbohydrates,lignin,fats,soaps,syntheticdetergents,proteinsandtheirdecompositionproductsas

alsoofinorganicsolids,pathogenssuchasbacteriaandvirusesandfinallynutrientsandgases.


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Table1,thechemicalcontentofdomesticwastewater(USEPA,2002).

TypicalRaw

Residential

Wastewater

Quality

Constituent MassLoadingGrams/person/day Concentration

5daybiologicaloxygendemand(BOD5) 3565 155286mg/l

Totalsuspendedsolids(TSS) 3575 155330mg/l

Chemicaloxygendemand(COD) 115150 150660mg/l

Totalnitrogen(TN) 617 2675mg/l

Ammonia(NH4N) 13 413mg/l

Nitritesandnitrates(NO3N)


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Currentwaterqualitystandardsofthearea,andwhatshouldbethestandardstoachieveafterwater

treatment. Secondly,wewillevaluatetheparametersthatweneedtotakeintoconsiderationwhen

lookingintothevariouswastewatertreatmentsolutionstoensureitsfeasibility.Thetotalcostrequired

inbuilding,operatingandmaintainingthewastewatertreatmentsolutionisaparameterfor

consideration.Itshouldbeaffordableforittobereadilyavailable.Stepsrequiredtooperateand

maintaintheplantifany.Arethehouseownerseducatedenoughtoservicetheirwaterplantorwould

theyhavetobringinatechnician.Theextenttowhichwaterqualitystandardscanbeattainedwiththe

implementedchoiceofsolutioncanbeanimportantfactor.

Methods

Septic Tank & drain field System

Background

Aseptictanksystemcomprisesofaseptictankthatitisconnectedtoaeitherasoiltreatmentsystem,

drainagesystem,oradrainfieldattheend(SPe,2015).Inthisstudy,wewillfocusonthemostcommon

typeofseptictanksystemwhichincludesaseptictankandadrainfield.Aseptictankisaconventional

wastewatertreatmentsystemthatishighlyefficientandselfcontained.IntheUnitedStatesalone,

approximatelyoneinfourhouseholdsutilizestheindividualseptictanksystemtotreattheirwaste

water(EPA,2014).

ConstructionTheseptictankisdesignedasawatertightboxthatisusuallymadeupofbricks,plastics,mortar,or

concretetopreventleakageofwaterintothesurroundingenvironment.Theapproximatecapacityof

theseptictankisabout4000to7500litres.Italsocomprisesofaninletpipe,wherebywastewaterwill

flowfromhomeintothetank,andaoutletpipe.Theshapeofthetankcanbeeithercylindricalor

rectangularandseparatedintotwochamberstoimprovetheremovalofsolids(UNEP,2015).

Figure1,aseptictanksystem(NewTechBio,2015).


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Asforthedrainfield,thedrainsshouldbeputdownhillfromthehousesothesystemcanworkwith

gravity,butifitsnecessaryandtheinfiltrationmustbeuphillitsalsopossibletouseapump.The

drainsshouldlayabout15cmdownfromsurfaceanditshouldalsobeabout1 2metersbetweeneach

pipe.(Naturvrdsverket,1987)Thisistoenabletheblackwaterfromtheseptictanktobedistributedto

thedifferentdrainsinanappropriatepace.Thedrainfieldconnectedattheendoftheseptictankisa

robustsolutionthatdontrequirealotofmaintenance.Italsodoesntrequirethatmuchelectricitywhy

itsagoodmethodinareaswherepowerfailureiscommon.Buttherightconditionsarenecessaryfor

thesystemtowork.Itsimportantthatthesoilisintherightfraction(likegravelorsand),itsnecessary

tohaveatleast50m2ofspacefortheinfiltrationdrains,anditsimportantthatitsasatisfyingdistance

downtothegroundwater.Thedrainfieldsystemcanbeusedincountriesallaroundtheworldandcan

beusedtotreatmixed,urine,blackwaterand/or

greywater.(Avloppsguiden,2015c)Disadvantageswiththesystemisthattheresariskofgroundwaterpollution,anditshardtotestthefunctionoftheinfiltrationandthequalityofthetreatedwatersince

itsallunderground.(Avloppsguiden,2015d)

Treatment and operation

ThemainfunctionaluseoftheSeptictankistoactasastoragetanktoholdthewastewaterlong

enoughforbothsolidsandliquidstobeseparatedbygravity.Inatypicalseptictank,thewastewater

canbestoredforabout24days(UNEP,2015).Thisallowsthewastewatertobeseparatedintothree

mainlayersaccordingtotheirdensity.Firstly,thetopmostlayeristhescumlayerwhichcomprisesof

solidssuchasoilsthatarelessdensethanwater.Secondly,thebottommostlayeristhesludgelayer

madeupfromsolidsthataredenserthanwater.Lastly,theremainingmiddlelayerwouldbethe

partiallyclarifiedfluid(NESC,2014).

Thesettledsolidswillundergoanaerobicdigestion bythebacteriainthewastewaterwhichcanreduce

thevolumeofsolids.Inthisoxygendeficientenvironmentcoupledwithwarmtemperatures,odor

producinggasessuchasmethanemaybeemittedandresuspendsettledsolids,increasingtheamount

oftotalsuspendedsolidsinthemiddlelayer(UniversityofMinnesota,2011).Assuch,additionaleffluent

screensmaybeaddedtoreducethedischargeofthesesolids.Theuseoftheseptictanktotreat

wastewaterenablesabout50%ofBODandsuspendedsolidstobesettledandremoved(UNEP,2015)

Theeventualeffluentwillbedischargedtoadrainfieldoraseepagefieldwherebytheremaining

impuritiesintheeffluentaretrappedandeliminatedinthesoilandtheexcesswateriseliminated

throughpercolationinthesoil,evaporation,plantuptakeorenteringthegroundorsurfacewater.

Inthedrainfield,thewaterisinfiltratedinthesoilwherebiological,physicalandchemicalprocesses

purifiesthewater.Thedrainsshouldbeputdowninalayerofbigfractionmateriallikebrokenstone,

macadam,orgravel.Butitsimportantthatthefractionofallthesoilisnttoobigsothewaterhavethe

timetopurifybeforegettingdowntothegroundwater.Itsalsoimportantthatthedistancefromthe

drainstothegroundwaterlevelislongenoughi.e+2m.Allwells,wetlandsandstreambedshouldnotbe

tooneartoaninfiltrationplant.(Avloppsguiden,2015c)


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Cost

Oneadvantageofthesmallscaleaerobicseptictanksystemisloweconomicalcostassociatedwithit.

Septictankscanbeeasilybuiltwithbasicmaterialsandnoadditionalenergyisneededtomaintainthe

tank.Furthermore,ithastheabilitytotreatsewerageonsite.Thisiswhyseptictanksareusually

situatedinruralareas,wherebythehousesarerelativelylargerandspacedfurtherapartastheoverall

costismoreeconomicalthanbuildingacentralisedsewersystem(NESC,2014).Inaddition,

transportationcostcanbesavedassewerageneednotbetransportedtoanearbytreatmentsystem.

Thedrainfieldsintheseptictanksystemhasalonglifetime,oftenmorethan20years,andsincethe

costofthemaintenanceisratherlowitsoftenconsideredaveryaffordablemethod.Themaincost

whenalltheworkisdoneinstallingthesystemisforemptyingoftheseptictank.

Thecostwilldifferalotdependingonthedifferentsoiltypesandhowbigtheinfiltrationplantshallbe.

Buttheaveragecostforthiskindofsystemwithgoodsoilconditionsareabout70000SEK.These70

000aredividedas25000fortheseptictank,about20000forthepipesandgravel,i.e.theinfiltration

plant,andthelast25000areforthework.(Infiltrationsanlggning,2015)

Maintenance

Septictanksrequirefrequentmaintenancewhichisoftentheresponsibilityoftheownerwhichincludes

theremovalofwastethatisnotdecomposedbyanaerobicdigestion.Theseptictankwillnotfunction

properlyifitisnotmaintainedandcanresultinserioushealthandenvironmentalconsequences.The

pumping frequencyoftheseptictankisdependantonboththetanksizeandthehouseholdsize(nesc,2004).Assuch,therehavebeengovernmentallegislationsuchasTheWaterServicesActin2012by

Ireland'sEnvironmentalProtectionAgencytoregisterallwatertreatmentsystemsandcarryout

inspectiontoensurewaterqualitystandards(EPA,2014).Forthedrainfield,itdoesntrequirealotof

maintenance.Ifitexistsanaerationtubeitshouldbecheckedoutaboutonceortwiceayearsoitsno

waterinside.Theseptictankmustbeemptiedregularlysotherestofthesystemdoesntgetclogged,

thisalsoshouldhappenaboutonceayear.(Avloppsguiden,2015d)

TheseptictankhasaBOD5removalof97%,aNH3removalof60%,removesnitrogento22%,Coliform

bacteriasto99%andphosphorousto12%(UNEP,1998).

Miniature water treatment plant

Background

Aminiaturewatertreatmentplant(MWTP)isasthenameimpliesasmallscaletreatmentplantthatcan

beusedforasinglehousehold.Themainadvantageswithminiaturetreatmentplantsarethattheydo

notrequireaninterventionintheproperty,aresmallandeasytocontrolandconsistofproven

technology(Avloppsguiden,2015b).MWTPsareusuallyusedinverysensitiveareaswhereahighdegree


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ofphosphorusandnitrogenremovalisneeded.IncertainareasaMWTPasthewastewatersolutionisa

requirementinordertogetabuildingpermissionforasinglehouse.

Thedegreeofpurificationfromaminiaturewatertreatmentplantdiffersbetweenmanufacturersbut

shouldreducephosphorousby7090%,nitrogen2050%coliformbacteria60%andBOD78095%

(Naturvrdsverket,2007b). Itsusuallyonlyrecommendedtouseaminiwatertreatmentplantfor

permanenthousings,duetoitbeingconstructedforacontinuousflowofsewagewaterandsinceit

requiresweeklysupervision.

Therearehoweverwaterplants,theyoftenusemembranetechnology,thatcanreachatreatment

efficiencyforCODat96.6%andBOD5at99.7%.Moreovertheyreachnitrificationandnitrogenremoval

efficiency61.0%.Regardingtheoverallsuspendedsolidsandphosphorusremovalefficiencytheyreach

at

99.5%

and

98%

respectively

and

faecal

coliforms

are

removed

at

99.99%.

Construction

Theminiaturetreatmentplantconsistsofallthepartsanormalwastewaterplantwould,justina

smallerscale.Theplantisburiedinthegroundoutsidethehouseanddoesnormallynotleaveanodour.

TheexactdesigndiffersbetweenthedifferentmanufacturersbutaMWTPfromBioKubeispresented

inthefigurebelow.Wherepoint13isthesludgeseparation,5isthedegradationoforganicmaterial,6

isthenitrogenpurificationand7isthenitrogenandphosphorusremoval(IFwater,2015).

Figure2,aminiaturetreatmentplantfromBioKube(IFwater,2015)

Anothertypeofminiaturewaterplantismembranebioreactor.TheMBRtechnologyintegratesthe

biologicaldegradationofwastewaterpollutantswithmembranefiltration,ensuringtheeffective

removaloforganicandinorganiccontaminantsandbiologicalmaterialfromdomesticwastewater

(Pikorova,2012).


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Thesetypesofsmallscalewastewatertreatmentplantsusuallyusethreetanksandarecomprisedof

threetreatmentsteps;thepretreatment,theaerationandthefiltrationwiththeuseofmicrofiltration

membranes.Thesystemisconsistedofthreemaintanksandoptionaltheyarecombinedwithtwo

smallertanksforphosphoruselimination.Thesystemcanbeinstalledinbasementsusingthe

gravitationalforcetoreceivethewaterorinsurfaceroomsinwhichthewaterisledbyapump.Excess

sludgeisrecirculated.Thefilteredwatercanbereusedforirrigationorflushingtoilets.Inthiswaythe

consumptionofdrinkingwaterinahouseholdcanbereducedbyatleastonethird.Ifthiswaterisnot

intendedtobereused,itcanalsobedischargedinsensitiveareassinceitisharmless.


Thewastewaterisledtoaminiaturetreatmentplantburiedinthegroundoutsidethebuilding

(Naturvrdsverket,2007a).Thewastewaterisfirstsubjectedtoamechanicalpurificationintheformof

sludgeseparation.Biologicallydegradablecoarsematerialsuchasfecalmatterandtoiletpaperare

dissolvedandasieveisusedtoseparatethenondissolvingcomponentsfromthewastewater.

Then,apumppumpsthewaterfromwhichthecoarsematerialhasbeenseparatedandleadsittothe

aerationsection.Inthissectiontheorganicmatterinthewastewaterisdegradedbiologicallyby

microorganismsandatmosphericoxygenwhichisblownintothetankbycompressors.

Itsafterwardstreatedchemicallyand/orbymembranefiltration.Duringthechemicaltreatmenta

precipitantisaddedtothewastewatermakingphosphorousflockandsinktothebottom.Thetreated

waterisafterwardsledtoforexampleatrenchoranothercompartmentwithintheplant,for

remediationwherenitrogenandothercontagioussubstancesareremoved(Avloppsguiden,2015a).Its

notuncommonforasamplingwell,monitoringthewaterquality,tobeplacedintheoutflowofthe

plant.Someplantstreatthesewagewatercontinuouslywhileothersdoitinbatches,calledSBR

technology.ThetreatmentcycleinaSBRplantisdescribedinthefigurebelow.

IfthewateristreatedthroughMBR,itwillpassthroughamembranefilterinsteadofundergoa

chemicaltreatment.Usuallyultrafinefilterswitha0.4mporesizeareusedtoeliminatesuspended

materialaswellasbacteriaandgermsandfinallytotallyclear,odourless,hygienicallyharmlesswater

leavesthesystem.Hydraulicretentiontimesareabout420hourswhichisenoughtimeforthe

oxidationoforganicmaterialandnitrificationtotakeplace(Bernaletal,2002).

Thephosphoruseliminationisaccomplishedbyadsorptionongranulesinsidethetwomodules.Since

thistechnologyconsistsofbiologicaltreatmentandmembranefiltrationinoneprocess,noadditional

treatmentprocesseslikesandfiltersorotherclarifiersareneeded.Moreover,duetooldersludgeage

andhighermixedliquorsuspendedsolids,MBRsproducelesssludgeandalsocantreatahighercapacity

ofwastewaterinthesamefootprintasacommonwastewatertreatmentplant(Bernaletal,2002).In

conventionalsystems1kgCODwillresultinabout0,3 0,4kgofbiomass.WithMBRsystems1kgCODis

convertedto0 0,2kgbiomass.


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Cost

Miniaturetreatmentplantsarerelativelyexpensivetooperate(about30006500SEK/year)duetothe

consumptionofelectricityandchemicalcomponents.Componentsforthebiologicalandchemical

purificationhavetobeaddedafewtimesduringtheyear.Thecostforatreatmentplantwith

installationisabout100000SEK.

MBRwastewatertreatmentplantsforsinglehousesarecurrentlyavailableforapproximately25000

77000SEKperunit.Moreovertheinstallationcost dependingonunitsizeandshape isabout25000

SEK.Powercostsareabout300SEKperyearbecausethetransmembranepressurehastobemaintained

ataspecificlevelandalsothecostsforaerationarehigh,especiallyathighersludgeconcentrations

(Mulleretal.).heannualcostofdesludgeandmaintenanceisaroundat10000SEK.Thisrangeofcosts

maketheMBRtechnologysystemsoneofthemoreexpensiveforsinglehouseholduse.

Maintenance

Theplantsrequiresupervisionbytheusersonceaweekwherethechemicalcomponentshavetobe

refilledandthemechanicalfilterhastobecheckedandperhapscleaned.Itrequiresservicebya

technician14times/yearandsludgeremoval12times/year(Avloppsguiden,2015b).

ForaMBRmaintenancealsoincludescleaningofmembraneelementswhenthetransmembrane

pressurerisestoexcess(Bernaletal,2002).Suchapressureincreasecanbecausedwhencontaminants

clogtheporesofthemembranesurface.Almostallcleaningproceduresareperformedautomatically.In

combinationwiththeaerationforthebiomass,aircanbeinjectedatthemembranebottominorderto

preventfoulingandcloggingofthemembranessurfaces.Acombinationofbackflushing,relaxationand

chemicalcleaningisalsoemployedtomaintainthepermeabilityofthemembranes.Manysystemsare

designedwithapressurizedbackflushsystemthatremovesthebiofilmfromthemembranesurfaceby

reversingthepermeateflowandpumpingitbackintothemembranes.Chemicalcleaningofthe

membranesismoreeffectiveandimprovesthefiltrationperformanceoftheelements.Chemical

cleaningconsistsofreverseflowofachemicalsolutionthroughthemembranesforovertwohours

(Bernaletal,2002).Chemicalslikesodiumhypochlorite,oxalicacid,citricacidandmorecanbeused.

Constructed Wetlands

Background

Constructedwetlandsarenaturalwastewatertreatmentsystemsandcanbeusedasasecondary

treatmentfacilitywhichcanbeusedinmediumsizedcommunitiesespeciallyindevelopingcountries

(wsp,2008).Thesewetlandscanbeusedtotreathouseholdwastewatersuchasblackwaterorgrey

water.Avarietyofcomplexbiological,physicalandchemicalmechanismsareusedintreatingthewater

andimprovingitsquality.Theremovalefficiencyoftheconstructedwetlandsismainlydependenton

thefiltermaterialandthehydraulicsurfaceloadingrate.


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Construction

Constructedwetlandsareconstructedbyexcavation,backfilling,gradingandinstallingwatercontrol

structurestoensuredesiredhydraulicflowpatterns(wsp,2008).Therearethreemaintypesof

constructedwetlands.Theyare:freesurfaceconstructedwetlands,horizontalflowconstructed

wetlandsandverticalflowconstructedwetlands.Amongthesethreedifferenttypesofconstructed

wetlands,theverticalflowconstructedwetlandisthemostefficientandrequirestheleastamountof

areaforconstruction,almost1to3squaremetersperperson.Usuallythereisaseptictank(anaerobic

digestion)oranaerobictreatmentunit(aerobicdigestion)forpretreatmentinordertoreduceorganic

matterandsuspendedsolids.Eachfiltershouldhaveanimpermeablelinerandacollectionsystemfor

theeffluent.


Therearethreemaincomponentsintheconstructedwetlands.Firstly,theimpermeablelayerthatis

usuallymadeupofclay(EPA,2015).Thispreventstheinfiltrationofwastewaterintothelowerground

aquifers.Secondly,thegravellayerwhichprovidesnutrientsandsupportfortherootzone.Thegravel

layerandrootzoneiswherewaterflowsandbioremediationanddenitrificationtakeplace.Constructed

wetlandstakeupnitrate/nitriteintheplantsorchangeittogaseousformsofnitrogen.Removalof

phosphorousislimitedbyhowmuchcanbetakenupbysoilandthesmallamountthattheplantsand

livingorganismsuseforgrowth.Themorephosphorousneededtoberemoved,thelargerareais

needed.Thefinalvegetativelayerthatisabovegroundcontainsplantmaterial.Inthewetland,both

aerobicandanaerobicprocessesexistatthesametime.Theanaerobiccellutilisesnaturalanaerobes

andplantstodegradethecontaminants.Atthesametime,theaerobiccellimproveswaterqualitywhen

plantsareexposedtothemovementofwaterbetweencellcompartments.Fortheremovalofmetals,

straw,manureorcompostcanbeusedinthesewetlands.Phytoremediationisthemainprocessusedin

constructedwetlandsasplantsareusedtobreakdownthecontaminants.

Cost

Thecapitalcostoftheconstructedwetlandisusuallylowandislessexpensivetobuildthantraditional

watertreatmentplants(wsp,2008).InthecaseofCentralAmerica,capitalcostofasubsurface

horizontalflowconstructedwetlandusuallyrangesfromUS$50to$100perpersonservedbythe

systemthatincludespretreatment.

Maintenance

Firstlytheseptictankhastobepumpedeverythreetofiveyearsforsludgeremoval(wsp,2008).During

thefirstdaysofoperationoftheplant,weedremovalisimportantasitcompeteswiththeplanted

vegetation.Distributionpipeshavealsotobecleanedonceayearforsludgeandbiofilmremoval.

Restingintervalswillalsohelpgravelnottoclog,otherwiseifthisisnoteffective,thecloggedpartsof

thefiltermaterialhavetobereplaced.Maintenanceactivitieshavealsogottoensurethatprimary

treatmentiseffectiveatreducingsolidsconcentrationofthewastewaterbeforeitentersthewetland.


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Table2,theremovalcapacityofconstructedwetlands(wsp,2008).

Parameter Influent Effluent Removal(%)

mg/l g/(m2 d) mg/l g/(m2 d)Suspended

solids

98.6 5.22 13.6 1.06 86

BOD5 97 4.8 13.1 0.89 86Total

nitrogen

28.5 1.15 18 0.78 37

Totalphosphorus

8.6 0.33 6.3 0.26 27

Case study

Location

ThelocationchosenforthecasestudyisafarmcalledKarleboatthecountrysideinstergtlands

CountyinthesoutheastofSweden,about170kmsouthofStockholm.Theagricultureatthefarm

consistsbothofbigfieldsaswellasanimalfarming.

Figure3,locationofthehouseinthecasestudy(eniro,2015).

Itsapermanentresidenceofabigfamilyandthenearestneighborlivesapproximate200metersaway.

ThemainhouseislocateduphillfromalakecalledSvinstadssjnwithahorizontaldistanceofabout200

m. Thelakeisabout1.85km2andtherearealargenumberofsummercottagesandvacationhomesin

theareaaroundthislake(Linkping,2004). Theresidencesinthesearetohigherdegreestartingtolive

inthemonapermanentbasis,somethingthattheirsewagesystemsarentreallydimensionedfor. The

lakeSvinstadsjnsuffers,likemanyotherlakesinthearea,fromproblemswitheutrophicationwhich

makethequestionofagoodwastewatertreatmentprocessevenmoreimportant.Thetotal

phosphorouscontenthavebeenupto210g/lwhichisconsideredveryhigh,andtheSecchidepthis

oftenlessthan0,5m.

Geology

Thegeologyofthelocationconsistsmostlyofclay(YellowinfigureX).Butrightatthelocationofthe

houseisaratherlargeareaoftill(blue)andalsosomebedrock(red)


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Figure4,geologyattheplaceofinterest.Itsalsopossibletoapproximatethedistancetothelake(upperright

corner).Yellow=Clay,Red=Bedrock,Blue=Moraine(sgu,2015)

ThegroundwaterlevelattheareaofthefarmcanbeobtainedfromtheSwedishdirectoryofwells

(brunnsarkivet).Attheareaofthehousethereare3differentwellsandthegroundwatertableisabout

4to5metersundergroundlevel.

Protection level

TheCountyofLinkpingdecideswhatkindofprotectionlevelthatisappliedforeachhousehold

(Linkping,2014).Therequirementsforhighprotectionlevelareanyofthefollowing:

Ifthehouseiswithin500metersfromopenwater.

Ifthehouseisinawaterprotectionarea.

Ifthehouseiswithinanareathatneedtobeprotectedofanotherreason.

Ifthehouseholdmeetstherequirementsofhighprotectionleveltherearespecialrulesabouthow

muchpollutionthewastewatertreatmentplantcanrelease(Naturvrdsverket,2006).

.Theselimitationsare:

Thewastewatertreatmentshouldachieveatleast90percentreductionoforganicmaterial(measured

asBOD7)

Thewastewatertreatmentshouldachieveatleast90percentreductionofphosphorus(totP)and 50

percentreductionofnitrogen(totN)

Thewastewatertreatmentenablesrecyclingofnutrients


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Discussion and conclusion

Themainfactortoconsiderwhenchoosingatreatmentmethodintheareaofourcasestudyisthatthenitrogenandphosphorousremovalishighanddependable.Thecost,maintenanceandeverythingelse

areallsecondaryfactorsinthiscase.Outofthefourmethodspresentedwewouldthereforeonlybe

abletouseaminiaturewaterplantoramembranebioreactor.

ThetoughregulationsinLinkpingscountymakeitimpossibleoratleastverydifficulttouseanyother

methodthanthewastewaterminiatureplant.InSwedeningeneralweseethattheregulationson

phosphorousandnitrogendischargearegettingharderandharder,andofcoursethisreducethe

numberofmethodssuitableforthearea.Inthespecificstudyareathereisalakelessthan500meter

awaythatalreadyhaveproblemwitheutrophication.Tonotgetthelakeinevenworseconditionits

importantthattheseregulationsarefollowedandtheformerwastewatertreatmentisprobablyoneof

thebiggestsourcesfortheproblem.Inalesssensitiveenvironmenttheseptictankofcoursewouldbea

preferablemethodfortheusersinceitrequiresbothlessworkwiththemaintenanceandalsoless

yearlycostfortheuser.Inthiscasethough,theenvironmentaladvantagesofmoreremovalofnitrogen

andphosphorousiswinning.

Theseptictankishighlyadaptableanditpresentvariousadvantagessuchasloweconomicalcostasthe

constructionandmaintenancecostassociatedwithitislower.Also,theremovalefficiencyofBODand

fecalcoliformsisveryhigh.However,theseptictankhasalimitationandthatisthelowpercentage

removalofnutrients,withalow12percentremovalofphosphorusand22percentremovalofnitrogen.

Inthecontextofourcasestudy,thecountryofLinkopinghasverystrictregulationtowardstheeffluent

anditscontents,wherebytheeffluenttreatwatershouldhaveachieveatleasta90percentreductionin

phosphorusand50percentreductioninnitrogen.Thisistominimisetheimpactsofeutrophicationdue

tothedischarge.Astheeffluentoftheseptictankdonotmeetthelegislativerequirementsofourcase

study,itisnotthemostoptimalsolution.

Similarly,bytakingtheeffluentqualityandthenitrogenandphosphoruscontentintoconsideration,

constructedwetlandsmightnotbethemostoptimalsolutiontoo.Constructedwetlandsarerelatively

inexpensivetobuildandeasytomaintain.However,theeffluentquality,thoughhighandBODandCOD

removal,thenutrientslevelstilldonotmeettherequirementsinthecountryofLinkping.Fromhere,

wecananalysethatthesesolutionsareeffectiveintreatingwaterqualityandcostfriendly.However,

whenweneedtoconsiderthecontextofthelocalmunicipalitywhichincludesthetypesofregulations,

costeffectivemethodsmaynotbethebestafterall.

Afterevaluatingthedifferentwastewatertreatmentmethodsandthecasestudy,wehavechosenthe

miniaturewatertreatmentplantasourchoiceofsolutiontosmallscalewastewatertreatmentinsingle

houses.


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ReferencesAvloppsguiden,(2015,a),

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small scale wastewater treatment for single houses

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