Reverseosmosisdesalination:Watersources,technology,andtoday'schallenges

WaterResearch

Reverseosmosismembranetechnologyhasdevelopedoverthepast40yearstoa44%shareinworlddesaltingproductioncapacity,andan80%shareinthetotalnumberofdesalinationplantsinstalledworldwide.Theuseofmembranedesalinationhasincreasedasmaterialshaveimprovedandcostshavedecreased.Today,reverseosmosismembranesaretheleadingtechnologyfornewdesalinationinstallations,andtheyareappliedtoavarietyofsaltwaterresourcesusingtailoredpretreatmentandmembranesystemdesign.Twodistinctbranchesofreverseosmosisdesalinationhaveemerged:seawaterreverseosmosisandbrackishwaterreverseosmosis.Differencesbetweenthetwowatersources,includingfoulants,salinity,wastebrine(concentrate)disposaloptions,andplantlocation,havecreatedsignificantdifferencesinprocessdevelopment,implementation,andkeytechnicalproblems.Pretreatmentoptionsaresimilarforbothtypesofreverseosmosisanddependonthespecificcomponentsofthewatersource.Bothbrackishwaterandseawaterreverseosmosis(RO)willcontinuetobeusedworldwide;newtechnologyinenergyrecoveryandrenewableenergy,aswellasinnovativeplantdesign,willallowgreateruseofdesalinationforinlandandruralcommunities,whileprovidingmoreaffordablewaterforlargecoastalcities.AwidevarietyofresearchandgeneralinformationonROdesalinationisavailable;however,adirectcomparisonofseawaterandbrackishwaterROsystemsisnecessarytohighlightsimilaritiesanddifferencesinprocessdevelopment.ThisarticlebringstolightkeyparametersofanROprocessandprocessmodificationsduetofeedwatercharacteristics.

Advancesinseawaterdesalinationtechnologies

Desalination

Anumberofseawaterdesalinationtechnologieshavebeendevelopedduringthelastseveraldecadestoaugmentthesupplyofwaterinaridregionsoftheworld.Duetotheconstraintsofhighdesalinationcosts,manycountriesareunabletoaffordthesetechnologiesasafreshwaterresource.However,thesteadyincreasingusageofseawaterdesalinationhasdemonstratedthatseawaterdesalinationisafeasiblewaterresourcefreefromthevariationsinrainfall.Aseawaterdesalinationprocessseparatessalineseawaterintotwostreams:afreshwaterstreamcontainingalowconcentrationofdissolvedsaltsandaconcentratedbrinestream.Theprocessrequiressomeformofenergytodesalinate,andutilizesseveraldifferenttechnologiesforseparation.Twoofthemostcommerciallyimportanttechnologiesarebasedonthemulti-stageflash(MSF)distillationandreverseosmosis(RO)processes.Althoughthedesalinationtechnologiesarematureenoughtobeareliablesourceforfreshwaterfromthesea,asignificantamountofresearchanddevelopment(R&D)hasbeencarriedoutinordertoconstantlyimprovethetechnologiesandreducethecostofdesalination.Thispaperreviewsthecurrentstatus,practices,andadvancesthathavebeenmadeintherealmofseawaterdesalinationtechnologies.Additionally,thispaperprovidesanoverviewofR&Dactivitiesandoutlinesfutureprospectsforthestate-of-the-artseawaterdesalinationtechnologies.Overall,thepresentreviewismadewithspecialemphasisontheMSFandROdesalinationtechnologiesbecausetheyarethemostsuccessfulprocessesforthecommercialproductionoflargequantitiesoffreshwaterfromseawater.

Potentialofheatpipetechnologyinnuclearseawaterdesalination

Heatpipetechnologymayplayadecisiveroleinimprovingtheoveralleconomics,andpublicperceptiononnucleardesalination,specificallyonseawaterdesalination.WhencoupledtotheLow-TemperatureMulti-EffectDistillationprocess,heatpipescouldeffectivelyharnessmostofthewasteheatgeneratedinvarioustypesofnuclearpowerreactors.Indeed,thepotentialapplicationofheatpipescouldbeseenasaviableoptiontonuclearseawaterdesalinationwheretheefficiencytoharnesswasteheatmightnotonlybeenhancedtoproducelargerquantitiesofpotablewater,butalsotoreducetheenvironmentalimpactofnucleardesalinationprocess.Furthermore,theuseofheatpipe-basedheatrecoverysystemsindesalinationplantmayimprovetheoverallthermodynamicsofthedesalinationprocess,aswellashelptoensurethattheproductwaterisfreefromanycontaminationwhichoccurundernormalprocess,thuspreventingoperationalfailureoccurrencesasthiswouldaddanextralooppreventingdirectcontactbetweenradiationandtheproducedwater.Inthispaper,anewconceptfornucleardesalinationsystembasedonheatpipetechnologyisintroducedandtheanticipatedreductioninthetritiumlevelresultingfromtheuseofheatpipesystemsisdiscussed.

Waterdesalination:AnimperativemeasureforwatersecurityinEgypt

WaterDesalinationisanindispensableindustryforthemostoftheArabcountries.Inthelastfourdecades,thenumberandcapacitiesofdesalinationunitshaveincreaseddramatically(45%Multi-StageFlash(MSF)and42%ReverseOsmosis(RO)ofworldcapacity);especiallyintheGulfStates.AlmostallavailableconventionalwaterresourcesinEgypt-representedbytheNilewater,renewablegroundwater,andsomescantannualprecipitation-havebeenexhausted.Furtherdevelopmentmeasuresrequirereviewofcurrentwaterallocationsinordertoraiseefficienciesandprotectagainstpollution,inadditiontoexploringnewoptionsofnon-conventionalwaterresourcestonarrowthegapbetweenwatersupplyanddemand.ThesemeasuresarethepillarsofEgypt'sintegratedwaterpolicyandhavebeenclearlypostulatedinitsNationalWaterResourcesPlan2023.TheobjectiveofthispaperistostudyandinvestigatewaterdesalinationasasolutionforwaterscarcityinEgypt.Moreover,thepresentworkdemonstratesthesignificanceofseawaterdesalinationfornationaldevelopmentinEgypt.Atpresent,Egyptisencouraging,notonlythepublicsectorbutalsotheprivatesector,toapplymoderntechnologiesfordesalination,whichhistoricallystartedwithDistillationthenElectrodyalisisandfollowedbyRO.Thegreatachievementsindesalinationtechnologyhavenowmovedthecostsfordesaltinginmanyapplicationsfromtherealmof"expensive"to"competitive".CurrenttechnologyisfeasiblefortouristvillagesinthenorthcoastandtheRedSea,duetoitsfardistancesfromconventionalsourcesthatmakesthecostofwaterconveyanceveryhighandsubjecttopollutionproblems.Theresultsindicatedthat,inspiteofresearchanddevelopments,stilltheenergyrequirementandmembraneknow-howarelimitingfactors.Thus,Egypt'sfuturevisionisnon-traditionalinthefieldofdesalination.Itisbasedonarealbreakthroughtowardstheuseofrenewableenergy,namely,solarenergytobeharnessedforoperatinghighcompressionpumpsneededforreverseosmosismodularsystems.Thereasonsareobvious,sinceEgypthasgreatpotentialofbrackishwaterwells,immenseamountsofsolarradiationinremoteareasandfutureintegrateddevelopmentprojectsarelocatedatadistancefromtheNilewater.ThistrendiswhatEgyptisfocusingonasaprospectivefutureforwideapplicationsofdesalination.Finally,thisresearchconcludedthat,thewaterdesalinationasaconventionalwaterresourceshouldbeconsideredasanimperativemeasureforwatersecurityinEgypt.Thefutureuseofsuchresourcefordifferentpurposeswilllargelydependontherateofimprovementinthetechnologiesusedfordesalinationandthecostofneededpower.

AdvancedenergeticsofaMultiple-Effects-Evaporation(MEE)desalinationplant.PartII:Potentialofthecostformationprocessandprospectsforenergysavingbyprocessintegration

Thispaperrepresentsthe2ndpartofapaperintwoparts.InpartIa2ndPrincipleanalysisofaMultiple-Effects-Evaporation(MEE)processhasbeenproposed.InthisPartIIperspectivesforprocessimprovementwillbeinvestigated,alongtwodistinctresearchlines:thethermoeconomics-aidedoptimizationofanewsystemandtheincreaseofthermalefficiencyforexistingsystemsbyapinch-basedplantretrofit.Asconcernsthefirstresearchline,adetailedproductivestructurefortheplantstage(i.e.effect)examinedinPartIispresented;thecostformationstructureisthenusedtoimproveasimplifiedoptimizationprocess,revealingcapabletoproperlyreflecttheinteractionsamongexergyflows.Itisshownthattheflashatbrineinletandtheexergydestructionatthepre-heaters,bothapparentlyplayingasecondaryrolewithrespecttoheattransferattheevaporators,becomemainsourcesofirreversibilitywhentheΔTbetweentwoconsecutiveeffectsincreases.Then,asacorollarytothelowexergeticefficiencycalculatedinPartIofthispaper,thepotentialforexergysavingthroughprocessintegrationisdiscussed.Althoughdetailedcalculationsarenotincluded,aconceptualapplicationofpinch-basedtechniquesisproposed,whichrevealsscarcemarginsforintegrationatprocesslevelandamuchhigherpotentialforprocess/hot-utilityintegration.TheuseofheatcascadescanbeoptimizedlookingattheThermalDesalinationProcessasablackbox;economicsofcogenerationsystemsintegratedwiththedesalinationplantandtargetedonheatsupply,infact,essentiallydependsonthecostoffeedsteam,fuelandelectricity.

Feasibiltystudyofrenewableenergypoweredseawaterdesalinationtechnologyusingnaturalvacuumtechnique

RenewableEnergy

Withanever-increasingpopulationandrapidgrowthofindustrialization,thereisgreatdemandforfreshwater.Desalinationhasbeenakeyproponenttomeetthefuturechallengesduetodecreasingavailabilityoffreshwater.However,desalinationusessignificantamountofenergy,todaymostlyfromfossilfuels.Itis,therefore,reasonabletorelyonrenewableenergysourcessuchassolarenergy,windenergy,oceanthermalenergy,wasteheatfromtheindustryandotherrenewablesources.Thepresentstudydealswiththeenergy-efficientseawaterdesalinationsystemutilizingrenewableenergysourcesandnaturalvacuumtechnique.AnewdesalinationtechnologynamedNaturalVacuumDesalinationisproposed.Thenoveldesalinationtechniqueachieveremarkableenergyefficiencythroughtheevaporationofseawaterundervacuumandwillbedescribedinsufficientdetailtodemonstratethatitrequiresmuchlesselectricenergycomparedtoanyconventionaldesalinationplantoffreshwaterproductionofsimilarcapacity.Thediscussionwillhighlightthemainoperativeandmaintenancefeaturesoftheproposednaturalvacuumseawaterdesalinationtechnologywhichseemstohavepromisingtechno-economicpotentialprovidingalsoadvantageouscouplingwithrenewableenergysources.

EvaluationoftechnologiesforadesalinationoperationanddisposalintheTularosaBasin,NewMexico

AccordingtotheUnitedNationsEnvironmentProgramme,one-thirdoftheworld'spopulationlivesinasituationofwaterstress.InthecaseofNewMexico,about90%ofthe1.8

millioninhabitantsdependongroundbrackishwaterastheironlysourceofpotablewaterinmanyareasofthestate.Thisreportpresentsatechnically-supported,economically-feasibleandenvironmentallyfriendlyproposaltodesalinatebrackishwatertosupplypotablewatertoinland,isolatedcommunitiesinsouthwestNewMexico.Severalexistingtechnologieswerereviewedtoidentifyopportunitiesforoptimizationbycombiningthemtoprovidepotablewaterandreducethewastestream.Alternativeswerestudiedandexperimentationwasconductedforsomeofthem.Thealternativesproposedweretheuseofnaturalcoagulantsforpretreatment,varioussolarcollectors'arrangementsforenergysupply,reverseosmosis(RO),lowtemperaturemulti-effectdistillation(LT-MED),multi-stageflashdistillation(MSF),solardistillation(SD),andelectrodialysisfordesalinationprocess;SpirulinacultivationandSDforwastetreatment,anddeepwellinjection(DWI)forwastedisposal.Somealternativeswereeliminatedbecausetheyareeithertechnologicallyoreconomicallynotfeasibleforthiscaseandpresenthighenvironmentalimpact.Threeplantconfigurationswereanalyzed.OptionAinvolvesusingthelinearFresnelsystems(LFS)toproducesteamforthefirsteffectofanine-effectevaporationplant.Thenumberofeffectswasdeterminedtoachievetheoptimalrelationbetweenequipmentinvestmentcostsandsteamproductioncost.Thisplantoperates8

hperdaywithsolarenergyandtherestofthe24

houroperatingtimeisprovidedwithfossilfuels.ThewasteproducedwillbefurtherevaporatedwithSDtominimizeitsflowandtheconcentratedbrinewillbeinjectedintoadeepwell.OptionBhasthesameelementsasoptionA,exceptthatitdoesnotconsidertheSD,butdirectbrineinjectionintoadeepwell.OptionCconsiderstheuseofSDastheonlyprocessfordistillationwithDWIasthewastedisposalmethod.Theselectioncriteriaforthebestconfigurationwereoptimaluseofsolarenergyresources,minimizationoffossilfuelconsumptionandwastestreamgenerationanddisposal.Operationrequirementsandeconomicanalysiswereconsideredtoselectaproposaleasytoimplementandoperateinruralisolatedcommunities.ForthefollowingreasonsoptionAisthebestconfigurationtocoverthenecessityofpotablewaterinNewMexico:(A)theplantiseasytoconstructandoperate.Inaddition,itcanhandledifferentrangesofbrackishwaterflow.(B)The76%waterrecoveryofthesystemalmostmatchestherecoveryachievedinaROplant(80%),withtheadvantagethatmaintenancecostsarereducedandtreatmentflowratescannotbematchedbytheROplant.(C)UseoftheLFSreducestheemissionofcombustiongasestotheatmosphereby33%.ThismanifestsasapositivepointinaLCAevaluation.(D)Theminimumenvironmentalimpactoftheprocessfacilitatesthepublicinvolvementplan(PIP)becauseitgivestheplantanenvironmentallyresponsibleimageintermsofavoidinggreenhousegasesemissions.(E)Thereturnoninvestment(ROI)is10.2%atapriceof$5.00/m3ofdesalinatedwater,whichissuperiortotheestimatedminimumattractiverateofreturn(MARR)usedforLT-MEDplantsas9.5%annually.

Technicalandeconomicassessmentofphotovoltaic-drivendesalinationsystems

Solardesalinationsystemsareapproachingtechnicalandcostviabilityforproducingfresh-water,acommodityofequalimportancetoenergyinmanyaridandcoastalregionsworldwide.Solarphotovoltaics(PV)representanideal,cleanalternativetofossilfuels,especiallyforremotecommunitiessuchasgrid-limitedvillagesorisolatedislands.Theseapplicationsforwaterproductioninremoteareasarethefirsttobenearingcost-competitivenessduetodecreasingPVpricesandincreasingfossilfuelpricesoverthelastfiveyears.TheelectricityproducedfromPVsystemsfordesalinationapplicationscanbeusedforelectro-mechanicaldevicessuchaspumpsorindirect-current(DC)devices.Reverseosmosis(RO)andelectrodialysis(ED)desalinationunitsarethemostfavorablealternativestobecoupledwithPVsystems.ROusuallyoperatesonalternatingcurrent(AC)forthepumps,thusrequiringaDC/ACinverter.Incontrast,electrodialysisusesDCfortheelectrodesatthecellstack,andhence,itcanusetheenergysuppliedfromthePVpanelswithsomeminorpowerconditioning.Energystorageiscriticalandbatteriesarerequiredforsustainedoperation.Inthispaper,wediscusstheoperationalfeaturesandsystemdesignsoftypicalPV-ROandPV-EDsystemsintermsoftheirsuitabilityandoptimizationforPVoperation.ForPV-ROandPV-EDsystems,weevaluatetheirelectricityneed,capitalandoperationalcosts,andfresh-waterproductioncosts.Wecoverongoingandprojectedresearchanddevelopmentactivities,withestimatesoftheirpotentialeconomics.Wediscussthefeasibilityoffuturesolardesalinationbasedonexpected(orpredicted)improvementsintechnologyofthedesalinationandPVsystems.ExamplesareprovidedforMiddleEastandotherpartsoftheWorld.

Amulti-barrierosmoticdilutionprocessforsimultaneousdesalinationandpurificationofimpairedwater

Osmoticdilutionincreaserejectionoforganicandinorganiccontaminants.OsmoticdilutionreducesenergydemandofseawaterROdesalination.Membranefoulinginosmoticdilutionisminimallydependentonwaterquality.Membranefoulinginosmoticdilutioncanbecontrolledbysystemconfiguration.

DesalinationofbrackishriverwaterusingElectrodialysisReversal(EDR):ControloftheTHMsformationintheBarcelona(NESpain)area

The4.5

millioninhabitantsoftheBarcelonametropolitanareaaremainlysuppliedwithsurfacewaterfromtheLlobregatandTerriverbasins.TheLlobregatriverwaterhasconsiderableconcentrationsofsalts,NaturalOrganicMatter(NOM)andhightemperature(T),causingimportantlevelsofTrihalomethanes(THMs)alongdrinkingwaterprocess.

ApilotstudywascarriedoutusingElectrodialysisReversal(EDR)toassessitsimplementationasanewdesalinationstepintheprocessofdeliveringdrinkingwater.After28

monthsofstudy,theaveragereductionvalueswereforbromide>

75%andforElectricalConductivity(EC)>

65%,whilewaterrecoverymaintainedalevelof>

90%.Additionally,theEDRstephasimprovedthechemicalandaestheticqualityofdrinkingwaterandallowsaTHMs-FormationPotential(THMs-FP)thatislowerthantheregulatedlevelof100

μg/L.

Thefinaldecisionwastheenlargementoftheplantproductionfrom3

m3/sto4

m3/sandtheinclusionofanewEDRstepafterGranularActivatedCarbon(GAC)filtration,withaproductioncapacityof2.3

m3/s,whichmakesthisplanttheworld'slargestdesalinationplantusingthistechnology,andanewexampleofalargescaleapplicationofadesaltingtechnologytoimprovethequalityofdrinkingwater.

Institutionalandpolicyframeworkanalysisinrelationtotheapplicationofautonomousdesalinationsystems—Greece

NewproposedsystemforfreezewaterdesalinationusingautoreversedR-22vaporcompressionheatpump

Modelingandoptimizationofasolardrivenmembranedistillationdesalinationsystem

Thedesalinationtechnologyusingmembranedistillationdrivenbysolarenergyisafeasiblesolutionforreducingtheenergycost.Adynamicsimulationmodelforasolardrivenmembranedistillationdesalinationsystem(SMDDS)isdevelopedontheAspenCustomModeler?(ACM)platformforthesystemperformanceandoptimizationstudy.Therigorousmodelforthespiral-woundairgapmembranedistillation(SP-AGMD)moduletakesintoaccounttheheatandmasstransferresistancesassociatedwitheachcomposinglayer.Theeffectsofadoptingdifferentobjectivefunctions,solarradiationconditions,thermalstoragetankconfigurations,aswellastheflowratesofthemembranedistillationmoduleandthethermalstoragetankontheoptimizedperformancearereported.Simplethermalstoragetankandlowerflowrateofthemembranedistillationmoduleareadvantageoustohigherwaterproductionrate.A

controlsystemusingconventionalPI(Proportional/Integral)controllersisproposedandthewaterproductionratecanreachabout87%oftheoptimalresultforclearskyoperation.

DesalinationplantsinAustralia,reviewandfacts

Australiaisthedriestcontinentonearthanddespitethistheinstalleddesalinationcapacityisstillaround1%ofthetotalworld'sdesalinationcapacity.Thispaperreviewsthemainseawaterissuesconsideredineverydesalinationproject—thehistory,thepresentsituationandthefutureofdesalinationinAustralia,thesuitabilityofapplyingreverseosmosis(RO)andtheprojectdetailsoftwodesalinationplants(SydneyandPerth).Oceancurrents,seawatertemperatureandsalinityaresignificantindicatorsintheassessmentofthefeasibilityofdesalinationastheyaffecttheproductioncosts,themaintenancefrequencyandthequalityoftheproductwater.Seawaterreverseosmosis(SWRO)istheonlytypeofdesalinationtechnologycurrentlyusedorproposedforfuturelarge-scaledesalinationplantsinAustralia.EverycapitalcityexceptDarwinhasconsideredbuildingatleastonedesalinationplantasameansofprovidingwatersecurityafterseveralyearsofunprecedenteddroughtthathassignificantlyreduceddamstoragelevels.Perthwasthefirstmajorcitytousedesalinatedwaterfordrinkingwatersupplyandbyearly2023Sydneywillbethesecondcity.Thirteenotherlarge-scaleSWROplantsarebeingplannedorproposedatseverallocationsforthepurposeofsupplyingdrinkingwater.

ProspectsofoperationofMSFdesalinationplantsathighTBTandlowantiscalantdosingrate

Controlofscaleformationonheattransfersurfacesisoneofthebasicproblemsinthermaldesalinationprocesses.Thereareseveralcommercialantiscalantsavailableinthemarketmostlyderivedfromcondensedpolyphosphates,polyelectrolytesandorganophosphonates.Acomprehensivestudywascarriedoutfordirectperformancesincomparisonofthreeofthemostwidelyusedantiscalants.Theyincludeamaleicacidbasedcopolymerantiscalant#1,amaleicacidbasedcopolymerantiscalant#2andaphosphonatebasedantiscalant#3.ThecomparativestudywasperformedinaMSFpilotplantunderharshoperatingconditions.Foreachofthethreeantiscalants,theMSFpilotplantwasoperatedataTBTof119

°C,adoserateof1

ppmandabrinerecycleconcentrationfactorof1.9foronemonth.AbaselinetestwasperformedunderthesameTBTandconcentrationfactorwithouttheuseofanantiscalant.Testresultsrevealthatantiscalantswerequiteeffectiveinsuppressingscaleformationundertheselectedoperatingconditions.ItisrecommendedtoreconsidercurrentscalecontroloperatingconditionsofcommercialMSFplantsespeciallywithregardstooptimizationofantiscalantdoserateandbrineconcentrationfactor.

InvestigationofanautonomoushybridsolarthermalORC–PVROdesalinationsystem.TheChalkiislandcase

Theuseofefficient,innovativeandcosteffectiverenewableenergysystemsinordertoproducepotablewaterseemstobeaverypromisingresearchobjectiveforscientists,engineersandeconomists,sincethechoiceoftheappropriatetechnologiesiscombinedwiththefactthatthesesystemsshouldbeeconomicallyfeasible.Thispaperpresentsageneralconceptofdesigningadesalinationsystemwhichusesasolarcollectors’fieldtodriveareverseosmosisprocessthroughanOrganicRankineCycle.Theauxiliaryequipmentpowerdemand(i.e.coolingpump,collectors’circulatorandworkingfluidpump)issatisfiedbyahybridsystembasedonaPVgenerator.AninverterisusedtoconverttheDCtoACcurrentwhileabatteryarrayisalsointegratedintothesystemasenergystorage.Inordertomakeacompletestudyofthesystem,thepumpingloadsthroughtheseaandtothearea’smunicipalwaternetworkhavebeentakenintoconsideration.

TheobjectiveofthecurrentworkistostudyanautonomousdesalinationsystemthatcanbeappliedtoseveralGreekislandswheretwoproblemsaretobesolvedatthe