The Cost of Cypress Wetland Treatment

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Title:
The Cost of Cypress Wetland Treatment
Series Title:
Cypress Swamps
Physical Description:
Chapter
Language:
English
Creator:
Fritz, Walter R.
Helle, Steven C.
Ordway, James W.
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University Presses of Florida
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Subjects / Keywords:
cypress swamp
nutrient removal
wastewater wetlands
wastewater treatment
Spatial Coverage:
United States -- Florida -- Alachua -- Waldo

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General Note:
Pages: 239-248

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University of Florida
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24The Cost of Cypress Wetland TreatmentWalterR.Fritz,StevenC.Helle,andJames vv. OrdwayAbstract Cypresswetlandsoffer a cost-effective means of ter tiary wastewater treatmentwhensite specific variables-costof land, length of force main required to get wastewater tothesite, average daily wastewaterflow,andwetlandtype-aretaken into account. Cy press strands, because oftheirlarge area,appearto be more economical for wastewater treatmentthandomes,whichareusuallysmaller and scattered. The utilization ofnumerouswetlandtreatment sitesmay be advantageous for a large regional facility.IntroductionThe decision tousecypress wetlands for tertiary treatment is highlydependenton cost. Generalized cost information forwetlandtreatment isnotavail 'ableduetotheuniquenessofeach wetlandsiteand "treatment situation. Costs for utilizing cypress wet"lands,however,shouldbeanalyzed todetermine(1),thecost-effectivenesscomparedto other tertiary treatment alternatives,(2)whichform ofwetlandtreatment ismostcost-effective, and(3)how to opti IIlize thecost ofthechosenwetland method. Comparison toOtherTertiary TreatmentAlterna thea:the mostcommontertiary treatment methods prestIyemployed are physical/chemical treatmentandapplication ofsecondarywastewater touplands24.1). Physical/chemical treatment involves complete tertiary treatment of wastewater at the treatment plant site. Typically, the process includes biological nitrificationanddenitrification of the wastewater to remove nitrogen. Phosphorus is gener ally removed by chemical means such asalumcoag ulation. The tertiary wastewater is commonly dis charged to percolationpondsfor final disposal. Wastewater from asecondarytreatment facility is oftenappliedtouplandareas where crops or natural vegetationcanremove nutrients. The wastewatercanbeappliedto the site as overlandflow,butis more commonly applied through a system of spray irriga tion nozzles. Normally,thewastewater percolates throughthesoil intoeitheranunderdrainsystemorthe groundwater. The cypress wetland tertiary treat ment alternative involves applying wastewater from asecondarytreatmentplantto wetlands where the vegetationandunderlyingsoils remove nutrientsandotherunwantedcontaminants. Boyle Engineering Corporationconducteda cost comparison analysis to determine the cost competi tiveness of cypresswetlandtreatmentwithphysi cal/chemical treatmentanduplandsprayirrigation (FritzandHelle 1978). U.S. Environmental Protec tion Agency(EPA)cost-estimating procedures were used for the comparison wherever possible(EPA1975a, 1975b). However, sinceEPAcost-estimating proceduresdonot exist for wetland application, costs for these alternatives were analyzed by quan tityandunitprice analysis. TheEPAcost figures re-239

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240Thewst of Wetland TreatmentfleetFebruary1973pricesandwereupdatedto Au gust1976usingthe :\ .... erage \\"astewater TreatmentPlantIndex(August1976=262.3,Base195i-1959=100). Costswerecomparedamongthealternativesfortertiarytreatmentonly. It is difficult todelineatethetertiarytreatmentportionsof the physicaL' chemicaloption.sothecosts for a typicalsecondarytreatmentfacility ..... eresubtractedfrom the totaltreatmentcost.Thecostsforbothuplandandwetlandtreatmentarehighlydependentonsitelocationandcharacteristics.Treatmentcostscanvarydramaticallydependingonthecostof land,distancefrom the treatmentfacility,andrequiredsiteimprovements. As aresultofthissitespecificity,thesethreeparametersremainedvariableinthecost analysis.Land A hydrologicloadingrate of 19mm,wkwascalculatedfromfieldtestdatatopreventoverflowwhenusingacypressdomethat has abermedperimeter.About2.8haofdomearea isrequiredforeachliterpersecondof flowatthisloading rate.Sincecypressdomesvaryinsizefrom 0.4 to 10haandareirregularinshape.it isunlikelythattheycanbepurchasedorleasedwithouttheinclusionofconsiderableportionsofsurroundinguplands.Forthisanalysis,allcypressdomesareconsideredtobe2hainsizewithanequalamountofsurroundinguplandsincludedinthepurchase.Cypressstrandswereassumedtohave25mmofsecondarywastewaterappliedeachweek.withabout2haneededforeachliterpersecond.Cypressstrandsoftenexistinlarge acreages.anditwasassumedthatalltherequiredwetlandareacouldbefoundinasinglestrand.Consequently.noadditional purchase oflandwouldbereqUired.Landrequirementsforthesprayirrigationsitearebasedon5mmwastewater/wkanda 60-mbufferareasurroundingthesite.LandrequirementsforphysicalJchemicaltreatmentareincludedintheEPA cost-estimating procedures.Severaltypicalcostsofland, both wetlandandupland.arerepresentedby thevaluesshownoneachindividualcurveinFigures 24.2-201.5. FairlylowvaluesofSOandS2500/hawereusedforthecypressstrandalternativesincethisoptiongenerallyrequiresmostlywetland.whichhaslittleeconomic LANQ.l.PPI..:CAmNSPRAY :RRIGATIONB-J== ,..n.R)ItC[.....--:=.......nQN I' I I wETt.ANllAPl"t.JCAomN-CYPRESSOOMES'"""._.c."us:>ocs"L T ,.....,;>HY SICALCHEMICAL TREATFigure24.1.;Jrocesses involved in:hree:net hods Df:reat ment :or secondarilytreatedwastewater.value.Sincethecypressdomeandsprayirrigationoptionscaninvolvethepurchaseofconsiderableareas ofuplands.highervalues ofupto$12,500/hahavebeenincluded.Curves forothervaluescanbeinterpolatedorextrapolated fromthese curves. Force RequirementsCost ofland-applicationtertiarytreatmentisdirectlyaffectedbythedistancefromthesecondarytreatmentfacility totheapplicationsite. Increased costs resultfromthegreater capitalinvestmentrequiredfor forcemaininstallationandfromhigherpumpingcosts.Ingeneral.therequiredlengthofforcemainisdirectlyrelatedtothedistancebetweenthetreatmentfacilityandapplicationsite.Theexceptioniscypressdomeapplication.whereseveraldomesmayberequiredtotreattheflow from asingletreatmentfa cility. A forcemainnetworkisrequiredtoconveyaportionofthewastewatertoeachdome.Thedistributionpatternofthecypressdomesisoftenmoreimportantthanthedistancetothetreatmentfacilityindeterminingthetotal forcemainrequirements.ImprovementsCypressdomesnormallymay overflowontoadjoininglandsafterheavyrains.especiallyduringthe wet season.Overflow from sewagedomesmayormaynotbeacceptable.dependingontheuseand charac terofsurroundinglands.Bermsarounddome perim etersmayberequiredtokeepdomewaters from overflowing,anditisassumedinthecost analysisti f

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Fritz, Helle,and Ordway241zo16A112AIlS whileeachcurve indicates a particular tertiary treatmentalternative and landcost combinatimLThe costcurvesforcypressdometreatment beginat valuesthatretlecttheestimated minimum force main net workrequired toaccommodatethese flowstoseveral" domes.Preliminarycostcomparisonsfor a particular case can bederivedfrom thecostcurves. The followinghypotheticalexamplewillillustrate theuseofthecost curves' for thispurpose.Asmallmunicipalitymustadd tertiary treatment toanexisting9115secondarytreatmentplant.Uponpreliminaryinvestigation.the followingaltematives are derived:(1)Usesprayirrigationona site located0.5 Ian from thetreatmentfacility. This landcouldbe8 12L.en;tIt 01 FOrce Main, 11m --$ J ZS 00 Po,oectarY'/jzsoo!'or-...../ /,/Nol.._e-.._.-----__ --------------------_.---NoUMcICas, ... 1 4/'/'.///./-'././------$10000 ---------------.-------Z41:::-=_:,::_=-=_=-:_=_=_:=ao=---.. ----35Fipn24.2.Costcurvesforthreetypes of wastewatera-tmeDt (750.000lJday). .. 8 ---o thatbermsare required. Costs fortheberms were es timatedbasedonaberm1m highandonSl.641m' -::" for construction.Likewise.fencing maybe required. topreventpublic entrance whentheapplicationsite", islocatednear residences orrecreation areas.Itwas assumed thateachcypress domeand strand would have awoven wire fence installed along itsperimeter '.. ata totalcostof$3.75/m.Fencingcostsareincorpo"" .rated into EPAcost-estimating procedures forspray'Irrigationandphysical/chemical treatment. ;' CostCurves ""The costcurvesinFigures24.2-24.5illustratethe results ofthecostanalysis described above.Eachfig 'lirerepresentsan individual averagedaily

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242 TheCostof Cypress Wetland Treatment 3530 ooQ l:!. Ii uCypress0cypas Strands SprayInigotlan4 812 Len9th Of ForceMain.bn 16 FipnZ4.3.Costcurvesforthreetypes of wastewatertn!8tment (1.900.000 Uday).purchased for$5000/ha.(2)Usecypressdomesinthe area.Thesize and positioning ofthedomesnecessitatea 6.5-lan-longfoice main network tointerconnectsixdomes.Itis estimated thelandcouldbe purchased for$25001ha.(3)Pumpthe eftluent toa large cypressstrand located 1.25 km fromthetreatmentfacility.Theseswamplandscouldbepurchasedfor$2500Jha.Whichalternativeisthemosteconomicallyattractive?From Figure 24.2thefollow ingcosts for tertiary treatmentwerefound:(1)$0.24/1000I:(2)$0.26/1000I:(3)$0.22/1000LFromthe precedinganalysis.alternative 3. utilizing cypressstrandapplications. appears mostec0nomicalat$0.22/1000l.Alternative1.involving sprayirrigation. isquite competitive at $0..24/1000 L Thecypress domealternativeisthemost costly,primarilyduetotheextensive force mainnetworkand large totaldomeperimetertobefencedand diked. Cypress wetlands can cleerly offeracosteffectivemethodfor tertiarytreatment undercertainconditions.Waldo. FloridaAsite specific costanalysis of severaltertiarytreat mentalternativeswasconductedfortheCityofWaldo,Florida.aspartof astudytoimprovetheir wastewater treatmentprogram(Ordway1976b; see alsochap.26). Wastewater fromWaldoistreatedina septic tank and discharged intoa which CODveys someof

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Fritz. Helle. and Ordway243 $12500Per "'eefer. // CYP"ess Domes Cypress Strands SprayIrriqationPl'lysicOI -Qlemic:alNo I._Cos,-------------__---,/'.--. ./'./---'-"' --5 .-C'!!!J--.-----o o 2 a... c .. uFipreZ4.4. Cost curves forfour types of wastewater treatment(3.750.000llday).1.Secondarytreatmentwithdischarge to wetlands: Capitalcosts$0.18/1000 I+wetlandcosts Operationandmaintenancecosts $0.18/1000 I+wetlandcosts Total $0.36/1000 I+wetlandcosts 2.Secondarytreatmentwith spray irrigationonuplands:CapitalcostsSO.26/1000 I Operationandmaintenancecosts SO.26/1000ITotal $0.52/1000 I 3.Secondaryandadvancedwaste treatment with nitrogenand phosphorus removal: Capital costs SO.34/1000 I ZO 16a IZLMqf" of Fotc.Main,11m4 thiswater to a 2.6-hacypressstrand (Fig. 24.6). The volumeofflowthroughtheseptic tanJc isabout 0.9-1.3lis.Thequalityofthe discharged wastewaterdoesnotgenera1Iymeetprimarytreatmentstandards.Anengineering firm representingthecityre viewedseveral possible treatment alternatives that wouldcomplywithstateandfederal requirements governing the treatmentanddisposal ofmunicipal wastewaters. Thealternatives listed belowandtheir ,"C"estimated costs arebasedonan anticipated flow of 5.2 lIs-day bytheyear1990(personalcommunica .'tfon: J.J. Parrish). Capital costs wereconvertedto treatment costs/3780 I (1000gal)of treatedwaste water basedonamortization at 6% for the 2Q-yruse:fullife ofthe facilities.

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244 TheCost of Cypress Wetland Treatment zs /--$SOOOPerhectareCypress Oomes Cypress Stran02sSprayPtlysical-O\emocat NoLooncl Costs --------------"Ho-L.;,;c;.-;.-----------------Pwhlctare _----_.------NoL.C!'!4.-----Ccats 4812 LtneJfh Of ForeeMoin.km 16 FIgureZ4.S. Cost curves for fourtypes of wastewatertreatment (7.soo.ooo Uday).Subtractionofthesecondarytreatmentcostsfromthesecondandthird alternatives yields: Costofsprayirrigation$0.16/1000ICostofadvancedwastetreatment$0.28/10001.Itisassumedthe city'ssecondary treatment facilitywillbelocatedinthesame area asthe existing septic tank sincethiswouldbecompatiblewiththeexist-OperationandmaintenancecostsTotal$0.30/1000I$0.64/1000Iingsanitarysewercollection system andwoulduse city-owned land. Consideringthis location, twopossible wetland disposal schemesare feasible. The firstincorporates thewetlandareas DUIJ'kedA. B,andCin FIgUre 24.6andresultsinaloadingrateof25mm1wk foraflowof5.2lis. Thereare. however.somedisadvantages to thisplan.Thestrands marked BandCbothreceive drainagefromthewest throughditchesandoverland flo\v, which would have tobe rerouted inorderto reducetheflushingaction thatnormally occurs duringthewet season. Additionally. these wetlandswouldhave to be hydrologically is0 lated(except for overflow) fromtheditches locatedalongtherailroad right-of-wa}t Theconstruction ope

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-..Figure 24.6. Proposedcypresswetland recycling systeminWaldo. Florida.erations necessary toachievethiswouldbe difficultinsuchtightquartersandwouldeliminatepartof theexistingwetlandarea.Furthermore.the purchase of thesewetlandareaswouldhavetoincludea con siderableamountoftheadjacentuplandarea.Thesecondwetlanddisposalsite.locatedeastofandadjacenttotherailroadright-of-way.hasseveral advantages:purchasewouldincludeonlya smallamountof theadjacentuplandtothesouth;therewouldbeonlyoneareato manage; itwouldnotbe necessary toreroutethedrainagearoundstrandsBandC;contactwiththerailroadwouldbelimitedto a single crossing;and.finally,drainagewaterenter ing fromtherailroadculverttotheeastwouldbe available todiluteanypollutantsremaininginthe wastewater after leaving the site.Fritz. Helle. md Ordway245:\preliminarydesignfor this siteconsistsof threeindividualwetlandareasdivided by3.1-:n earthen dike. Thiswould allow alternate 10acii.:Jgof the areas for management ofthe system. :\total area of16hawouldbe available for the treatment of secondary wastewaterwithaloadingrate ofapproximately19mmiwkfor a flow of 5.2 I.s. Irrigationcontrolstruc tures are located along the diketo permitthe use of various flowpatterns through the syste=:t andas a means of regulating water depth.:\nadditional10.5 ha of landsurrounding :hetreatmen: area are includedas a buffer. anda shallowswaie along thesouthernpropertyline would divert :unoff waters from the adjacentuplandarea.:\ holding basin near thesecondary :reatment facility would be usedtoallowthecontinuouspumpingof'sastewatertothe disposal sitebasedona 16-hr ciay. Thepiping system consists of 1700 m of diameterPVCforce main. Total cost forthiswetlandtreatmentsite wasSO.H/l000Icompared \.. ithS0.16/1000I for spray irrigationandSO.28/1000 I foradvanced .... aste treat ment. clearlydemonstratingcypresswetlandtertiary treatment alternatives to be cost-effecti \"e. ComparisonofCypressWetlandAlternativesTwomethodsofutilizingcypresswetlandsfor the tertiarytreatmentof wastewaterha\'ebeensug gested.Thefirstmethodinvolvespondingsecondarywastewaterincypresswetlandsandallowingit to percolatethroughtheorganiclayercoveringthe wet land's bottom.Treatmentoccurs by biological uptakeandadsorptionbyorganicandothersoillayers. This process ischaracteristicofcypressdomes.Thesecondmethodtakes advantageofbiological treatmentwhilethewastewateris flowing overthesurfaceofthewetland.Acypressstrandmaybe utilizedinthismannerbyapplyingsecondarywaste water alongtheupstreamedgeandallowingit to flowthroughthestrand.Oneadvantageofcypressstrands isthatthey arecommonlylargerandtherefore morelikelyto accom modatetheentirevolumeof wastewaterfroma treatmentfacility at asinglesite. Thiseliminatestheneedfor anetworkof force mainsandcomplexflow control devices.Thefollowing costanalysisfor asecondarytreatmentfacility. locatednearOrlando.

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246 TheCostofCypressWetlandTreatmentBasedonthese assumptions. :l:e=stimated treatment cost for the dome op::c::is 50.188 1000Icomparedto50.03911000liar :..::estrand option. The large cost differentialisdue pri:narHy tothe exten sive forcemainnetworkandthe longer total perime ter for fencesanddikes requiredin the dome system.OptimalUsageofCypress Domes Recent strategies for wastewater ::-eatment planninghave focused on large regional ::-eatment facilities.Thisapproachis generally belie';ec to reduce costsbytreatinganentire region's was,ewater at a single largefacility. The cypressdomemethod dces::ot appeartofitthispattern.L'nlike other processes that mayincreasein economy asthe size of thesystem(and treated \"olume) isincreased. a cypressdometreatmentsystemmay exhibit anoptimumtreatment cost atsomeflow thatislessthan the maximumca pability oftheavailablewetlandarea. Factorsthatwill have the greatest influenceontheoptimumcostofa specific cypress domesystem are the densityofthewetlandarea compared tothetotal land area.theaveragedomesize.andthe spatialpatternofthe ex istingdomes.Severalhypotheticalcypressdomesystemswereconsideredfor flow ratesof2.2. -l:.';. 22. -1-1. and 219lis(Fig. 24.8J. Average dome areas of 0.01.2 .. I:, and6hawereassumedforwetlandareasthatcomprise4%. 12.5%. and 25% of the totallandarea.Itwasassumedthatthesystem will beusedto recycle secondarilytreatedmunicipalwastewaterat a loading rateof2.5cm/wk.Thepumpingtimeforapplicationofwastewaterwasassumedtobeapproximately16hr/day.Thepumpingandpipingcostsfor the various flow ratesarebasedoncostsreportedbyOrdway(1976a). Alldomeswereassumed tobecircularinshapeandequallyspaced;thus.thedistancebetweendomesfor agivenaveragedomesize is a functionofthedensityofwetlandarea.Onlyunitpumpingandpipingcostswereconsidered with theassumptionthat allothercosts remain fixed foragivenunit flow rate.Thewetlandsystemsusedfor chis studywereassumedtocontainenough area for treatment ofatleast 219lis. with thetreatment facility locatednearthecenterofthewetlandsystem. Dispersal of waste.-'1;:[/;:;\=," .. :\01ps...../tt...= I / ".-;;";S\". -".;-1:''",.,.. '., j I fI.t;,.J>'e' : -. i Figure24.7. Proposedc:;press '.\etiandrecyciingat Or,lando :>:a\'al TrainingCenter :\nnex inOrlando,Florida (nf =forcemain:STP=secondarytreatmentplant).Florida.investigatesthecost of both of thesewetlandalternatives forthesamefacility.OrlandoWastewaterPlant 3. located attheOrlandoNavalTrainingCenter Annex. is a trickling filter facilitywithacapacityof 32 lis.Numerouscy pressdomessurroundtheannex.anda large wetlandstrand. Bog."oy CreekSwamp.is located 3 kIntothesouth(Fig. 24.7J. Ahydrologicloadingrateof19mm/wkwas assumedforcypressdomes. necessitating 160 ha ofdomes.It isunlikelythat thedomescouldbeobtainedwithoutthepurchaseof aconsiderableamountofthesurroundinguplands.Anestimated320ha (50% domesand 50% uplands)wouldhaveto bepurchasedatS7500/ha.Thenearest44domesarerequiredtosupplythe required 160haofwetlands.Secondarywastewaterisconveyedtoeachdomefor aprescribedlengthoftimeeachdayusinga forcemainnetworkandindividualautomaticvalvesandtimers.Theforcemainnetworkincludesmorethan27.500 mof6-and8-in.diameterPVCpipe.Fencesandearthendikesareincludedaroundtheperimeterofeachdome.Landcosts forcypress strand treatmentincludethepurchaseof160haofthemorethan24D-ha BoggyCreekSwampatanestimatedcostofS2500/ha.A 670D-m forcemainsystem(includingsevenmanual valvesandoutlets) is reqUired toapplythewastewaterinasheetflowarrangement.A fencewouldbebuiltaroundthepurchasedland. i l

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oo 10:; 35 c<1.l 30 CJ)f-2 25 uE 2 C[a:: 15 cOt-'Zil::E 5 ::>a..2xKi4xlO' I/ ,, ,i WETLANDS 12.5%OFTOTAL LAND AREA ii, 0.4 HEC7ARE 'DOMe:AREAl! Fritz. Helle.and Ordway247 WETLANDS25%CF iOTAL LAND ARE':' !!., ,i!:i II 'ii,;,;,HEC+.iRE iDOMe: II' ,, TOTALWASTEWATER FLOW. I/doy Figure 24.8. Optimumcostsiorcypressdome:reatment.water fromthetreatmentfacility isconsideredto be radiallyoutward.The estimatedunitpumpingandpipingcosts for the range of flow ratesupto219 lis (2x 10; IIday)areshowninFigure24.8.These costsincludetotalowningandoperating costsamortizedat6%overtheexpected life ofthesystem.Costs for a given flow rateandaveragedomesizedecrease asthedensity ofthewetlandsystemincreases.Optimumpumpingandpipingcosts,representedbylowpointsonthecurves.aremorepronouncedfor systems havingsmalleraveragedomesizesandalso for areas having asmallerpercentageofwetlands.Theoptimumflow rate ofwastewaterfor agivenwetlanddensityalso increases astheaveragedomearea becomes larger. Althoughtheexactspatialpatternofwetlandsassumedforthisanalysiswillprobably notbedupli catedinmanyexistingwetlandsystems.thegeneral cost trendsshownmaybesimilarto those found for domes. A flow-throughsystembasedoncypress strands. however.wouldbeexpectedto be more eco nomical for flows thatutilizethemaximumcapacity ofthesystem. Conclusions Cypresswetlandsmustbe economically attractivecomparedtoothertertiarytreatment alternatives in order to beconsidereda viable alternati .... e. The cost effectiveness of cypress wetland treatment is highly site specific,withthecostof land. length of required force mains. averagedailywastewater flow.andthetype of cypresswetlandandsurroundingsall beingimportantvariables.Thecost analysis for Waldo, Florida.indicatescypresswetlands tobethemost cost-effectivetertiarytreatment alternative for that situation. Two basic types ofcypresswetlandswampsare available for treating wastewater: cypressdomesandcypress strands. Cypress strands offeraneconomic advantage for larger treatment plants because they are often availableinlarger areas.Theywouldalsominimizethetotallengthof forcemainneededtoapplytheflowandlengthof wetlandperimeterthat mustbedikedorfenced. Comparison of the two methods for atreatmentfacility nearOrlando.Flor ida. revealed that itwouldcost over3timesasmuchtousecypressdomesinstead of asinglelarge wet landstrand.

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248i1Ieeo.t of Cypress WetlandTMatmmtRegjonaliutionhas oftenbeenthought tobethemost alSt-effective methodfor wastewater treatment planningfor allcases. However. investigation intotheuseofcypress domes for tertiary treatment has shownthatoptimumdailyflows exist foreachdistri-butionpatternof domes.This suggests thatoptimum sizedtreatment facilitiesplaced throughout the region would maketertiarytreatmentcostsmore attractive than onelarge regionalfacility if Cl'JlIdSi wetlandswereused.