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Desalination235(2009)58–870011-9164/09/$–Seefrontmatter©2009PublishedbyElsevierB.V.*Correspondingauthor.TowardssustainableseawaterdesaltingintheGulfareaM.A.Darwisha*,N.M.Al-Najema,N.LiorbaMechanicalEngineeringDepartment,KuwaitUniversity,KuwaitTel.+965498-5789;Fax+965484-7131;email:darwish@kuniv.edu.kwbDepartmentofMechanicalEngineeringandAppliedMechanics,UniversityofPennsylvania,Philadelphia,PA19104-6315,USAReceived26November2007;acceptedrevised19July2008AbstractGulfcountriesexperiencedrapidgrowthinthelastfourdecadesfromoilproductionanditspriceincrease.Naturalwaterresourcesareverylimitedtomeetthisgrowth,andasresult,desaltedseawaterinKuwaitbecamethemainsourceofpotablewater,about93%in2002.Theelectricpoweranddesaltedwater,producedinco-generationpowerdesaltingplants(CPDP),consumptionsarecontinuouslyincreasing,almostdoubledevery10years,duetopopulationandstandardoflivingincreases.Thisledtotheconsumptionofhugeamountsoffuel,drainingthecountrymainfuel(andincome)resource,andnegativelyaffectingtheenvironment.OnetenthofKuwait’soilproductionwasconsumedbytheCPDPin2003.Ifthetrendofalmostdoublingtheconsumptionevery10yearsprevails,thetotaloilproductionmaynotbesufficienttodesaltseawaterforpeopletodrink,andtoproducepowertorunspaceairconditioningunits(anecessityforKuwaitiharshweather).Itisessentialthereforetolookforenergyefficientwaystoproducepoweranddesaltedwatersoastosavethenation’sincomeofthesenon-renewablefuelresources,tosavetheenvironmentandindeedlifeitselfinKuwait,andthisistheobjectiveofthispaper.Itreviewsthepresentlyuseddesaltingmethodsandtheirenergydemand,andthecorrectnessoffuelallocationformulasforCPDP,todeterminethemostefficientmethodstoapplyandthelessefficientonestoavoid.Fourteendesaltingcasesareanalyzedbyusingthecurrentpractice,withandwithoutcombinationwithpowergenerationplants(usingsteamorgasorcombinedgas/steamturbinescycles).ThespecificfuelenergyconsumedandtheemittedCO2,SOx,andNOxperm3desaltedwaterwerecalculatedforeachcase.Theresultsshowthatoperatingthermallydrivendesaltingsystemsbysteamdirectlysuppliedfromfuel-firedboilersisthemostinefficientpractice,andshouldbeavoided.Theuseofthegas/steamturbinecombinedcycle,whichisalsothemostefficientpower-generationcycle,todriveseawaterreverseosmosis(SWRO)desalinationplantsisthemostefficientcombination.Also,allconservationmeasuresinutilizationofbothwaterandpowershouldbeapplied.Reclamationofwastewater,atleastfornon-potablewaterneedsmustbepromoted,becauseitconsumeslessenergyandatcostmuchlowerthanthoseofdesaltingseawater.Keywords:Waterdesalination;Steamturbinepowerplants;Gasturbinespowerplants;Combinedgas/steampowercycles;Dualpurposedesalinationplants;Energyconsumptionforwaterdesalination;Sustainability;Airpollution;CO2emissionsdoi:10.1016/j.desal.2008.07.005M.A.Darwishetal./Desalination235(2009)58–87591.IntroductionKuwait,likeotherGulfcountries,experiencedveryrapidgrowthinelectricpoweranddesaltedwaterproductioninthelastfourdecadesduetotheevolutionofoilproductionanditspricein-crease.Onemayask,isthisgrowthsustainable?Themostuseddefinitionforsustainability[1]isthegrowththatmeetsthepresentgenerationneedswithoutcompromisingfuturegenerations’abil-itytomeettheirownneeds.Daly[2]statedthatsustainabilityrequires:1.Theuserateofrenewableresources(e.g.groundwater)doesnotexceedtherateoftheirregeneration.2.Theuserateofnon-renewableresources(e.g.fossilfuel,mineralores)doesnotexceedthedevelopmentrateofsustainablesubstitutes.3.Thepollutantsemissionratedoesnottoex-ceedthecapacityoftheenvironmenttoab-sorbandrenderthemharmless.Whilemostofthedatausedinthispaperper-taintoKuwait,thegeneralsituationandtrendsofwaterandenergyuseandoftheirimpactonre-sourcesandtheenvironmentareverysimilarinmostoftheGulfcountries.Therenewableannualwaterresource(groundwater)inKuwaitislessthan100m3/capita*(notingthatannual1000m3/capitamarksthewaterpovertyline!),whiletheextraction(consumption)rateismorethan500m3/capita/y[5].Over-extractiondepletesthegroundwateranddeterioratesitsquality.WhileKuwaithaslargeamountsoffossilfueloil,whichcanbeusedforproducingnewwater,thatresourcehasothermajorusesandisfinite,withnopracticalalternativeforitssubstitution.*WaterreplenishmentinKuwaitcomesfromraintotheDammamlimestoneaquifersintheUmGhadirfieldalongtheborderofSaudiArabia,andaverysmallper-centageoftheprecipitationinfiltratesintotheground-waterinKuwait[3,4].Theestimatedrenewablewateris75m3/(capita·y)[5],butthecurrentextractionisabout510m3/(capita·y).Althoughfullsustainabilitymaynotseempos-sibleforthetimebeing,efficientpowerandwa-terproduction,alongsidewithmuchmoremod-estconsumption,areessentialtoallowthepresentresourcestomaintainthecountry’sdevelopmentoveralongertimeperiod,i.e.,tomakeitmoresustainable.InKuwait,about93%ofpotablewaterneedwassecuredbydesaltingseawaterin2002[6].Table1givestheinstalledcapacityofdesaltingunitsanddesaltedwaterconsumptioninthelastfourdecades.Thedaily-consumedfreshwaterinl/capitaincreasedfrom137in1973toalmost500in2003,andthepopulationincreasedfrom900,000in1983to2,540,000in2003,resultingina10-foldwaterconsumptionincreas