Managementof ConcentrateFrom DesalinationPlants
NikolayVoutchkov
GiselaNoelleKaiser
1.2 Enablingconditionsfordesalination.............................................7
1.3 Overviewofexistingconcentratemanagementpractices.............8 1.4 Concentratemanagementregulations............................................8
3.3 Concentratetreatmentpriortosurfacewaterdischarge..............54
3.4 Designguidelinesforsurfacewaterdischarges..........................56
3.5 Costsfornewsurfacewaterdischarge........................................60
3.6 Codisposalwithwastewatereffluent...........................................64
3.7
5.1 Description.................................................................................131
5.2 Potentialenvironmentalimpacts................................................131
5.3 Effectonsanitaryseweroperations...........................................131
5.4 Effectonwastewatertreatmentplantoperations......................132
5.5 Effectonwaterreuse.................................................................133
CHAPTER6Deepwellinjection
CHAPTER7Landapplication
CHAPTER9Zero-liquiddischargeconcentratedisposal
CHAPTER10Beneficialuseofconcentrate .................................. 209
10.1 Technologyoverview.................................................................209
10.2 Extractionofmineralsfromconcentrate...................................213
10.3 Feasibilityofbeneficialreuse....................................................220 References..................................................................................220
CHAPTER11Regionalconcentratemanagement 223
11.1 Typesofregionalconcentratemanagementsystems................223
11.2 UseofbrackishwaterconcentrateinSWROplants.................224
11.3 Jointdesalinationandreuse.......................................................226 References..................................................................................230
CHAPTER12Nonconcentrateresidualsmanagement .................. 231
12.1 Spentpretreatmentbackwashwater..........................................231
12.2 Chemicalcleaningresiduals......................................................242 Reference...................................................................................243
CHAPTER13Selectionofconcentratemanagementapproach 245
13.1 Concentratemanagementalternatives.......................................245
13.2 Thefutureofconcentratemanagement.....................................251
13.3 Concludingremarks...................................................................253 References..................................................................................256
Appendix1:Abbreviations...................................................................................257
Appendix2:Units..................................................................................................261 Glossary.................................................................................................................263 Index......................................................................................................................271
Preface
Thisbookprovidesanoverviewofthealternativesformanagementofconcentrategeneratedbybrackishwaterandseawaterdesalinationplants,aswellassitespecificfactorsinvolvedintheselectionofthemostviablealternativeforagiven project,andtheenvironmentalpermittingrequirementsandstudiesassociated withtheirimplementation.Thebookfocusesonwidelyusedalternativesfordisposalofconcentrate,includingdischargetosurfacewaterbodies,disposalto wastewatersystems,deepwellinjection,landapplication,evaporation,beneficial reuse,andzero-liquiddischarge.Directdischargethroughnewoutfalls,discharge throughexistingwastewatertreatmentplantoutfalls,andcodisposalwiththecoolingwaterofexistingcoastalpowerplantsaredescribed,anddesignguidancefor theuseoftheseconcentratedisposalalternativesispresentedwithengineersand practitionersinthefieldofdesalinationinmind.Keyadvantages,disadvantages, environmentalimpactissues,andpossiblesolutionsarepresentedforeachdischargealternative.Easy-to-usegraphsdepictingconstructioncostsasafunction ofconcentrateflowrateareprovidedforallkeyconcentratemanagement alternatives.
Atpresent,membranereverseosmosis(RO)desalinationisthefastestgrowing technologyforproductionoffreshwaterfromsalinewatersources:desalination plantsuselessenergytoproducethesamevolumeoffreshwaterthanthermal desalinationfacilities.Therefore,thisbookfocusesexclusivelyontheconcentrate managementofROdesalinationprojects.
Planninganddesignforlocating,construction,funding,andoperationofdesalinationplantsismorecomplexanddemandingthanthatforconventionalwater treatmentfacilitiesintermsofprofessionalskills,knowledgeandunderstanding oftheenvironment,treatmentprocesses,technologies,andequipmentemployed indesalinationprocesses.Astheadvancesindesalinationtechnologymakedesalinationmorecompetitivewithotheralternativesourcesofwatersupply,planning anddesign,includingpreparationofaccuratecostestimatesforconstructionand operationofdesalinationprojectsbecomesofcriticalimportanceforidentifying thesizeandroleofdesalinationinthemixofalternativesthatprovideasustainableandreliablewatersupplyportfolioformunicipalcoastalcentersaroundthe world.
Thisbookprovidesdetailedinformationonhowtomanageconcentrateinthe implementationofseawaterROdesalinationplants.Thebookcontains13chapters,coveringcurrentdevelopmentsindesalinationandessentialknowledgeof prevailingmethodsofconcentratemanagement.Easy-to-useformulasandcost curvesareincludedtofacilitatedevelopmentofestimatedvolumesandcosts associatedwiththevarioustypesofconcentratemanagement.
Chapter1,IntroductiontoConcentrateManagement,providesabriefreview tothecurrentstatusofdesalinationworldwideandanoverviewofthemostcommonlyusedconcentratemanagementalternatives.Withtheelevatedriskofwater
scarcityduetoclimatechangeanddemandgrowth,desalinationisbecoming increasinglypopularfortheproductionoffreshpotablewater,especiallyinhighly urbanizedcoastalregions.Asthenumberofplantsandvolumesofdesalinated waterincrease,assurancemustbeprovidedoftheenvironmentalsustainabilityof suchdischargesoverextendedtimeperiods.Potentialenvironmentalimpactscan beminimizedthroughtreatmentofconcentrateandoptimaldischargeconfigurationanddesign,eitherdirectlyintothewaterbodyordisposedtogetherwithtreatedwastewaterorcoolingwaterfrompowerplants.
Chapter2,DesalinationPlantDischargeCharacterization,presentsthekey componentsofdesalinationplantwastestreams.Dischargefromdesalination plantsisconstitutedmainlyofROconcentrate,butmayalsocontainsignificant volumesoffilterbackwashwaterandcleaningsolutionsusedinwaterconditioningandmembranecleaning.Thequantityandqualityofeachsourcecanbecalculatedbasedontheplantcharacteristics.Thevolumeofconcentrateisafunction oftheplantrecoveryrate,andgiventhelargevolumesdischarged,concentrate managementmustbeintegraltopreliminarydesigndecisions.
Chapter3,SurfaceWaterDischargeofConcentrate,coversthemostcommon desalinationplantconcentratedisposalpractice.Asthenumberofdevelopments andvolumesofdesalinatedwaterincreases,assurancemustbeprovidedofthe environmentalsustainabilityofsuchdischargesoverextendedtimeperiods. Potentialenvironmentalimpactscanbeminimizedthroughmixingofconcentrate withdischargesofwastewatertreatmentplantsorpowerplantgenerationstations, orbytheuseofdiffusersystemsforaccelerateddissipationoftheconcentratein themarineenvironment.Ifproperlymanaged,thefootprintofincreasedsalinity canbeminimizedresultingintheeliminationofpotentialnegativeimpactsof concentrateandotherdesalinationplantdischargesonthereceivingaquatic environment.
Chapter4,CaseStudiesforSurfaceWaterDischarge,includescasestudiesof concentratemanagementpracticesinAustralia,Israel,Spain,andtheUnited States.Mostlargeplantshavedirectdischargetosurfacewaterbodies.Inthis chapter,permittingpracticesarecomparedbetweencountries.Asthetechnology hasevolvedrapidlyoverthepastdecades,standardizationwithincountriesis oftenstilllacking–mostcountrieshoweverhavesimilarpermittingrequirements fordesalinationplantdischarges.
Chapter5,DischargetoSanitarySewer,addressesthedisposalofconcentrate tothewastewatercollectionsystemasacommonpracticefromsmalldesalination plants.Typically,smallvolumesofbrinearecombinedwiththeinfluenttolarge treatmentplants.Thecostofdischargerelatesonlytoconveyanceintothewaste streamandisthuslow.Concentrateismanagedasindustrialeffluentwithboth quantityandqualityregulatedtohavenonegativeimpactonplantoperations. Increasedsalinitycanhavepotentialimpactoneffluentreuse,especiallyfor irrigation.
Chapter6,DeepWellInjection,detailshowconcentratefromdesalination plantscouldbedisposedofindeepconfinedsalineaquifers.Thecapacityofsuch
aquifersislimitedbypermeabilityandtransmissivity,whiletheunderground injectionzonemustbecompatiblewiththewaterqualityofthemembraneconcentrate.Theinjectionzonereceivingconcentratemustalsobeover10,000mg/L TDS.Concentratemayrequirepretreatmenttopreventnegativeimpactsonthe receivingaquifer.Monitoringofgroundwaterinthearea,andpressureinthe aquiferarecriticaltoearlyidentificationofleaksandregulatingthisformof disposal.
Chapter7,LandApplication,explainshowconcentratecanbedisposedina mannerwhichinvolveseithersprayirrigationonsalt-tolerantplantsorinfiltration throughearthenrapidinfiltrationbasins.Landapplicationistypicallyusedfor smallvolumesofbrackishwaterconcentrateonlyanditsfull-scaleapplicationis limitedbyclimateconditions,seasonaldemandandbyavailabilityof suitablelandandgroundwaterconditions.Agriculturalapplicationstovegetation toleranttosalinityholdspromiseofimprovingbeneficialuse.
Chapter8,EvaporationPonds,describesthecircumstancesunderwhichconcentratecanbedisposedtoponds,wherewaterisevaporatedthroughsolarpower, whiletheremainingsaltsarecollectedperiodicallyincrystalizedformandtransportedtolandfill.Landareaneededforthepondsismainlydependentonthevolumeofconcentrateandthesite-specificevaporationrate.Additionalstorage capacityisrequiredtoallowforaccumulationofthemineralsthathavecrystalizedatthebottomoftheponds.Solarpondsareevaporationpondswithan enhanceddepthwhichareconfiguredtogenerateenergy.
Chapter9,Zero-LiquidDischargeConcentrateDisposalSystems,explores currentdevelopmentsinreducingbothenvironmentalimpactandcostofconcentratemanagementbysubstantiallyreducingconcentratevolumes.Zero-liquiddischargetechnologiesconvertconcentratetopurewateranddrycrystalsordense brinewhichcanbeeitherusedforcommercialpurposesordisposedoftoalandfill.Processintensificationcombinesanumberofexistingprocessestoimprove therecovery,butdisruptivetechnologiesarelikelytobenecessarytosignificantly reducecostsandenergyrequirements.
Chapter10,BeneficialUseofConcentrate,buildsonzero-liquiddischargein identifyingpotentialmarketsforthebyproductsderivedfromthebrinesuchas high-valuemineralsandraremetals.Beneficialuseofconcentrateprovidesthe opportunitytotransformdesalination,renderingitfarmoresustainablebynot onlyreducingthenegativeenvironmentalimpactofdischarge,butbyproviding revenuethroughmineralrecovery.
Chapter11,RegionalConcentrateManagement,introducestheintegrationof concentratefromvarioussourcesinrelativelycloseproximitytoexploitpotential efficiencies.Giventhecomparativelyhighcostofconcentratemanagement,benefitscanbeobtainedbyconsolidatingeffluentfromanumberofsourcestoprovide infrastructurethatminimizesenvironmentalimpactwhiletakingadvantageof economiesofscale.Usingavarietyofsourcesandtypesofeffluent(i.e.,brackish andseawater)hastheadvantageofdilutionthatcanfurtherpositivelyimpactthe environment.
Chapter12,NonconcentrateResidualsManagement,describesthedisposalof nonconcentrateresidualssuchasspentfilterbackwashwaterfromseawaterpretreatment,spentmembranecleaningsolutionsandotherprocesssidestreams. Pretreatmentbackwashquantityandqualityvariesdependingonwhethermembraneorgranularsystemisemployed.Wherequalityisnotdetrimentaltothe environment,spentbackwashwaterisblendedwithconcentrateanddischargedto waterbodies.Alternatively,on-sitetreatmentisrequiredpriortoblending. Chemicalsusedtoperiodicallycleanmembranesresultinresidualdischargethat typicallyneedstobeeithertreatedandblendedwithconcentratebeforedisposal, orconveyedtothenearbywastewatercollectionsystem.
Chapter13,OverviewofConcentrateSelectionManagementApproach,comparesthevariousmethodsofconcentratedisposalandhighlightstheiradvantages anddisadvantages.Feasiblemethodsofdisposalneedtobeidentifiedandthen costedforthelifeoftheproject.Feasibilityisinfluencedbyregulations,environmentalsensitivityandphysicalconstraints.Costofconcentratemanagementis impactedbythesizeofthedesalinationproject,sourceseawaterquality,thetype andsensitivityofthemarineenvironmentinthevicinityofthedischarge,and preventiveormitigationmeasuresthatneedtobeimplementedinordertominimizeenvironmentalimpacts.
Thisbookisintendedfordesalinationprojectplanners,engineers,and designers;waterutilityprofessionalsinvolvedindevelopmentofwaterresource managementplans;equipmentandmembranedevelopers;operationandtroubleshootingspecialists;aswellasforstudentsandteachersinthedesalinationfield. Itcontainsneed-to-knowdesalinationconcentratemanagementpracticesand information,whichwouldbenefitpractitioners,decision-makers,andscholars alike.
Introductiontoconcentrate management
Desalinationisbecomingincreasinglypopularfortheproductionoffresh potablewatersincemanyinlandandcoastalmunicipalitiesandutilitiesinarid regionsoftheworldarelookingfornew,reliable,anddrought-prooflocalsources ofwater.Climatechangeincreasestherisksofwaterscarcity,whichareamplifiedinvulnerablecommunitieslackingessentialinfrastructure.Desalinationisa tried-and-testedadaptationoptiontoincreasethereliabilityofwaterresourcesbut hasrelativelyhigherproductioncost,energydemand,andcarbonfootprintas comparedtoconventionalwatersupplyalternatives.Similartoconventionalwater treatmentplantsandwaterreclamationfacilities,desalinationplantsalsogenerate discharge,whichcontainstheplant’ssourcewatertreatmentbyproducts.Fora desalinationprojecttobeviable,plantdischargehastobedisposedofinan environmentallysafeandsustainablemannerthatiscompliantwithallapplicable governmentalregulatoryrequirements.
Oneofthekeylimitingfactorsfortheconstructionofnewdesalinationplants istheavailabilityofsuitableconditionsandlocationfordisposalofthehighsalinitywastestreamgeneratedduringthedesalinationprocess,commonly referredtoasconcentrateorbrine.Monitoringprogramsatexistingplantsworldwidehaveshownthatimpactsonthemarineenvironmentarenonexistentorvery limitedandlocalizedwithproperplantoutfallconfiguration,siting,anddesign. Publicizinginformationofsuchmonitoringprogramshavethecapabilityof improvingtrustindesalinationtechnology,andensuringenhancedsustainability offutureplantdevelopments.Thisbookprovidesanoverviewofexistingconcentratemanagementoptions,theiradvantages,disadvantages,andimplementation constraints.
1.1 Currentstatusofdesalination
Accessiblefreshwatermakesuponlyafraction( , 2.5%)oftotalwateronthe planet.Populationsaroundtheworldhistoricallyreliedonsurfacewater(from rainfall)andgroundwater,butbothofthesesourcesarevulnerabletochangesin climateandvariabilityinweather.Aspopulationsgrewinlocationswhere
freshwaterwasscarce,newsupplysourceswerepursued.Thefirstthermaldesalinationplantswerebuiltinthebeginningofthe20thcentury,whilethefirstcommercialbrackishandseawaterreverseosmosis(RO)plantscameintooperationin the1960sand1970s,respectively.Withtechnologyadvancing,recyclingand reuseofwaterisnowalsoviable,expandingtheoptionsofpotablewatersupply.
Asthecostofwaterincreasesthroughdiversificationofsupplybeyondrelianceonrainfall,sothevalueofwaterbecomesmoreapparent.Sustainablewater managementrequiresthatallwaterinthesystemisaccountedfor,anddemand managementformsanimportantaspectofreconcilingdemandandsupply. Demandmanagementshouldbethefirst,andisgenerallytheleastcostlyinterventiontostretchavailablesupply,buttherearelimitstoefficiencies,beyond whichadditionalwaterresourceswillinevitablyberequired.
Whilethevalueofwaterneedstobebetterappreciated,andtheworldaspires toacirculareconomyandclosed-loopresourcesystems,growthinpopulation andqualityoflifewillrequireadditionalpotablewaterintheforeseeablefuture. Theoceanhastwouniqueanddistinctivefeaturesasawatersupplysource:Itis drought-proofandispracticallylimitless.Overhalfoftheworldpopulationlives inurbancentersborderingtheocean.Inmanyaridpartsoftheworldsuchasthe MiddleEast,Australia,NorthernAfrica,andSouthernCalifornia,thepopulation concentrationalongthecoastexceeds75%.Usuallycoastalzoneshavethehighestpopulationgrowthaswell,resultinginseawaterdesalinationbeingalogical solutionforsustainable,longer-termwaterresourcemanagementtomatchgrowingwaterdemandpressuresincoastalareas.
Desalinationremovesthesalts,pathogensandimpuritiesfromsalinewaterto renderitpotable.Desalinatedwaterisproducedeitherfrombrackishwater(saline waterwithtotaldissolvedsolids[TDS]contentoflessthan10,000mg/L)orfrom seawater(TDSbetween30,000and50,000mg/L).Althoughbrackishaquifers andsurfacewatershavebeenusedforproductionoffreshdrinkingwaterforover 50years,thesebrackishwatersourcesareoflimitedavailabilityandhavealong replenishmentcycleresultinginlimitedlong-termsustainability.Incontrast,the world’soceanscontainover97%oftheplanet’swaterresources,providingan essentiallyunlimitedrawmaterialforseawaterdesalination.Inmosturbancenters,thefreshwaterproducedbydesalinationofseawaterisreturnedbacktothe oceanintheformoftreatedwastewater.Usuallywastewatertreatmentplantsare withina25 50kmradiusofthedesalinationplantsalongthecoastandthetime toreturnover80%ofthedesalinatedseawatertotheoceanaswastewaterdischargeistypicallylessthan1week.Mostoftheremaining20%ofthedesalinatedwaterislosttoevaporationandgroundpercolationasdrinkingwaterand wastewatergeneratedfromitaremainlyusedforirrigation.Thismakesseawater desalinationoneofthewatersupplyoptionswiththeshortestwatercycle,shorter thanlake,river,orbrackishwatersources.
Withgrowingwaterscarcityandsignificantlyreducedcost,interestindesalinationhasriseninrecentdecades.ThisisparticularlytrueintheMiddleEast, whereseverewaterscarcityandrelativelylowcostofenergyhavefacilitatedthe
earlyadoptionofdesalinationasamainsourceofpotablewatersupply.Driven byrisingdemandandcommercialinnovation,thecostofdesalinationhas decreasedsignificantlyovertime,andisbecominganincreasinglyfeasibleand sustainableoptionformostothercountriesworldwide.
Atpresent,over16,000desalinationplantsworldwideprovidedrought-proof watersupplyforalargenumberofaridurbancoastalmunicipalitiesofthe MiddleandFarEast,Europe,Africa,Australia,andtheAmericas(Jonesetal, 2018).Almosthalfoftheseplants(44%)areinthestillfast-growingMiddleEast region.However,otherregionsoftheworld,notablyAsia(inparticular,China), theUnitedStates,andLatinAmericaarealsoexperiencingaccelerateddesalinationplantcapacitygrowthof6% 8%peryear,whichfarexceedsthegrowthrate ofconventionalwatersupplysources(2% 3%peryear).
Productionoffreshwaterbydesalinationin2019totaledapproximately95 millionm3/day(24,300MGD).Thecorrespondingcumulativevolumeofconcentrategeneratedbythedesalinationplantsinoperationatpresentisestimatedtobe 142millionm3/day(37,500MGD).Approximately74%oftheexistingdesalinationplantsusemembraneROtechnologyforsaltseparation;21%applythermal evaporation;and5%useothersaltseparationtechnologies,suchaselectrodialysis (ED)andionexchange(IX)toproducefreshwater(see Fig.1.1).After2015, mostMiddleEasterncountrieshavedrasticallyreducedtheconstructionofnew thermaldesalinationplantsandhaverefocusedontheuseofmembranedesalinationduetoitslowerenergydemandandoperationalflexibility.
FIGURE1.1
Currentstatusofworldwidedesalinationtechnologyuse.
DatafromIDADesalinationYearbook2018 19.
Desalinationofbrackishandseawaterisbecomingincreasinglypopularfor productionoffreshpotablewaterintheUnitedStates.Basedona2017survey (Mickley,2018)atpresentthereareapproximately400desalinationplantsinthe UnitedStatesandtheirnumberisgrowingsteadily(see Fig.1.2).Mostdesalinationplantsusenanofiltration(NF)andROmembranesforsaltseparation.
Thesteadytrendofreductionofdesalinatedwaterproductionenergyandcosts coupledwithincreasingcostsofconventionalwatertreatmentandwaterreuse, drivenbymorestringentregulatoryrequirements,areexpectedtoacceleratethe currenttrendofrelianceontheoceanasanattractiveandcompetitivewater source.Thistrendislikelytocontinueinthefutureandtofurtherestablishocean waterdesalinationasareliabledrought-proofalternativeforamajorityofcoastal communitiesworldwideinthenext15years.Atpresent,desalinationprovides approximately10%ofthemunicipalwatersupplyoftheurbancoastalcentersin theUnitedStates,Europe,Israel,andAustralia,andover50%ofthedrinking wateroftheGulfCooperationCountries;by2030thispercentageisexpectedto exceed25%and80%,respectively.
Increasedrelianceonseawaterdesalinationisoftenparalleledwithongoing programsforenhancedwaterreuseandconservationwithalong-termtargetof achievingabalanceofconventionalwatersupplysources,seawaterandbrackish waterdesalination,waterreuseandconservationtothetotalwatersupplyportfoliooflargecoastalcommunities.Surfacewatersourcesareusuallysignificantly cheaperwithwell-developedmanagementsystemsandoperationsinplace.
FIGURE1.2
CumulativenumberofmunicipaldesalinationplantsintheUnitedStates.
Addingmorecostlydesalinatedwatertothesupplymixrequiresimproved demandmanagementandderivingfullvalueofreusepotentialtooptimizethe valueofpotablewater.
Near-andlong-termdesalinationtechnologyadvancesareprojectedtoyielda significantdecreaseincostsofproductionofdesalinatedwaterby2030.Indesalination,innovativetechnologieshavebeenaddressinglongstandingissuesthat havehamperedthedevelopmentofthisalternativeresource.Newtechnologies suchasnanoparticleenhancedmembranes,biomimeticmembranesandforward osmosisaswellasbeneficialextractionofraremetalsfromthebrinegenerated bydesalinationplantsareaimedatreducingenergyconsumption(by20% 35%), reducingcapitalcosts(by20% 30%),improvingprocessreliabilityandflexibility,andgreatlyreducingthevolumeoftheconcentratedischarge.
1.1.1 Desalinationasastrategicwaterresourceoption
Despitesignificantreductionincost,desalinationremainsmoreexpensivethan otherbulkwatersourcesandneedstobeusedstrategicallytoaddressalimited rangeofproblems.However,todaytheinstancesoftheseproblemsarefast expanding.Desalinationisprovingappropriateforcertainmarketsthatrequirea highqualityandcompletereliabilityofserviceandinwhichcustomersorgovernmentscanaffordtopaythehighercost.Forexample,desalinationcanproduce high-qualitypotablewaterthatsuitstheneedsoflargecitiesinwhichthereare highconcentrationsofpeoplewhodemandaquality24/7waterserviceandwho arepreparedtopayforthatservice.Desalinationcanalsoprovideareliablesupplyoflargevolumesofwatertohigh-valueindustry,commerce,andtourism. Theseusestypicallyvaluewaterappropriatelyandcanaffordtopayunsubsidized costforproductionofdesalinatedwater.
Desalinationisofspecificinterestincertainlocationsinwhichtheothersupplyalternativesareequallyormorecostlyand/ortheriskofsupplyfailureor inabilitytosecuresustainablealternativewaterresourcesishigh.Desalinationis, however,demandingintermsoflocation.Waterhasaveryhighratioofbulkto valueandisveryexpensivetoliftortransport.Thisdrivesthelocationofadesalinationplant:tobenearitssource,thesea,andtobeclosetoitsmarketorpoint ofuse.Hence,thetypicallocationofadesalinationplantisalongacoastalcity orcoastalindustrialzone,supplyingarelativelywell-offindustrial,commercial, ordomesticdemand.Wherethephysicalandsocioeconomicconditionsareright, seawaterdesalinationprovidesastrategicsolutionforthesustainable,long-term satisfactionofpartofthisgrowingwaterdemand.
Aswaterscarcitygrowsandwithadvancesindesalinationtechnologyand reductionsinproductioncost,policymakersaroundtheworldarerightfullyasking whetherdesalinationshouldplayapartinclosingthegapbetweensupplyand demandinfutureyears.Althoughmostofthesupply demandgapsolutionswill stillcomefromthetraditionalsupplyanddemandsidemanagementoptions, desalinationisoneoftheviableoptionswithstrategicrelevance.
Desalinationalsoprovidesasolidresponsetoexogenousriskssuchasdependency.Singapore,forexample,optedforlarge-scaledesalinationtoreduceits dependenceonincreasinglyexpensiveimportedwaterfromMalaysia.Thestable, efficientsuppliesofurbanandindustrialwaterthatdesalinationprovidescanhelp governmentsmanagearangeofeconomic,social,andpoliticalrisks.
1.1.2 Currentdesalinationprojectrisksandcosts
Desalinationprojectsareoftenmegasizedwithriskassessment,management,and mitigationcomprisingkeycomponentsofprojectplanning.Allbusinessdecisions requirenotonlyanassessmentofcostsandreturnsbutalsoanevaluationofthe risksattachedtoaprojectandmeasuresformanagingoreliminatingrisks togetherwithcontingencyarrangementsformitigatingpossibleimpacts.Clearly, therisksassociatedwithmegaprojectsareconsiderableandriskassessment formsakeypartofplanning.Keyrisksassociatedwithdesalinationprojects include(1)permittingorlicensingrisks,(2)entitlementrisks,(3)technology risks,(4)constructionrisks,(5)regulatoryrisks,(6)financialrisks,(7)source waterqualityrisks,(8)powersupplyrisks,(9)O&Mrisks,and(10)desalinated waterdemandrisks.
Selectingtherightprocurementmethodisimportantformatchingriskexposuretomanagerialcapacityandultimatelyachievingthebestvalueformoney. Thesponsorofaninfrastructureprojecthasalternativeoptionstodealwitheach oftheserisks:(1)decidetomanageit(keeptherisk),ifthesponsorbelievesthere isthetechnical,managerial,orfinancialcapacityrequiredtohandleit;(2)insure orhedgetherisk,ifandwherethemarketofferssuchsolutions;or(3)transferit orshareitwithathirdparty.Theconditionsunderwhichtheserisksaretransferredorsharedwithaprivatepartneraredeterminedbytheprocurementinstrumentadoptedtodeveloptheinfrastructure.Inturn,theselectionofthe procurementinstrumentshouldbemadetoallocatethedifferentrisksinvolved withthepartythatisbestplacedtomanagetheminacost-effectiveway,which isnotnecessarilyalwaystheprivatesector.
Commonlyuseddesalinationprojectdeliverymethodsinclude:
1. theturnkeyapproach,alsoreferredtoas“engineering,procurement,and construction”(EPC),inwhichtheprivatecontractorisresponsibleforthe designandtheconstructionofthefacility;
2. the“design build operate”method(DBO),inwhichthecontractorisalso responsiblefortheoperationoftheplantforalimitednumberofyears, usuallytwotofive;and
3. the“build own operate transfer”method(BOOT),bywhichtheprivate partnerfinancesthedesalinationfacilityandoperatesitforalongperiodof time,usually20 25years,inexchangefortariff-basedpaymentslinkedto plantcapacityandactualwaterdemand.
Thetraditionalinfrastructureprocurementapproach,alsoknownas “design bid build”(DBB),israrelyusedfordesalinationprojects.
1.2 Enablingconditionsfordesalination
TheadvanceoftheROdesalinationtechnologyissimilarindynamicstothatof computertechnology.Whileconventionaltechnologies,suchassedimentation andfiltrationhaveseenmodestadvancementsincetheirinitialusefor potablewatertreatmentseveralcenturiesago,newmoreefficientseawaterdesalinationmembranesandmembranetechnologies,andequipmentimprovementsare regularlyreleased.Similartocomputers,theROmembranesoftodayaremany timessmaller,moreproductiveandcheaperthanthefirstworkingprototypes. ThefutureimprovementsofROmembranetechnologywhichareprojectedto occurby2030areforecasttoencompass:
• developmentofmembranesofhighersaltandpathogenrejection, productivity,reducedtrans-membranepressure,andfoulingpotential;
• improvementofmembraneresistancetooxidants,elevatedtemperature,and compaction;
• extensionofmembraneusefullifebeyond10years;
• integrationofmembranepretreatment,advancedenergyrecovery,andSWRO systems;
• integrationofbrackishandseawaterdesalinationsystems;
• developmentofnewgenerationofhigh-efficiencypumpsandenergyrecovery systemsforSWROapplications;
• replacementofkeystainless-steeldesalinationplantcomponentswithplastic componentstoincreaseplantlongevityanddecreaseoverallcostofwater production;
• reductionofmembraneelementcostsbycompleteautomationoftheentire productionandtestingprocess;
• developmentofmethodsforlow-costcontinuousmembranecleaningwhich allowreductionindowntimeandchemicalcleaningcosts;and
• developmentofmethodsforlow-costmembraneconcentratetreatment,inplantandoff-sitereuse,anddisposal.
Althoughnomajortechnologybreakthroughsareexpectedtodramatically reducethecostofseawaterdesalinationinthecomingyears,thesteadyreduction ofdesalinatedwaterproductioncostscoupledwithincreasingcostsofwatertreatmentdrivenbymorestringentregulatoryrequirements,areexpectedtoaccelerate thecurrenttrendofincreasedrelianceontheoceanasanattractiveandcompetitivewatersourceby2030.
Thistrendisforecasttocontinueinthefutureandtofurtherestablishseawater desalinationasareliabledrought-proofalternativeformanycoastalcommunities
Table1.1 Forecastofdesalinationenergyuseandcostsformediumand largeplants.
Parameterforbest-inclassdesalinationplants202020222030
Totalelectricalenergyuse(kWh/m3)3.5 4.02.8 3.22.1 2.4
Costofwater(US$/m3)0.8 1.20.6 1.00.3 0.5
Constructioncost(US$/MLD)1.2 2.21.0 1.80.5 0.9
Membraneproductivity(m3/membrane)28 4855 7595 120
worldwide.Thesetechnologyadvancesareexpectedtoentrenchthepositionof SWROtreatmentasviableandcost-competitiveprocessforpotablewaterproductionandtoreducethecostoffreshwaterproductionfromseawaterby25%in 2022andbyupto60%by2030(see Table1.1).
Therateofadoptionofdesalinationincoastalurbancentersworldwideis dependentonthemagnitudeofwaterstresstowhichtheyareexposedandavailabilityoflower-costconventionalwaterresources.
Infuture,desalinationislikelytobeadoptedasmainwatersupplyinaridand semi-aridregionsoftheworldsuchandtheMiddleEast,NorthAfrica,the WesternUnitedStates,andAustraliaandinlocationsofconcentratedindustrial demandforhigh-qualitywatersuchasSingapore,China,andNorthernChile.
1.3 Overviewofexistingconcentratemanagement practices
Accordingtothe2018reportonconcentratetreatmentpreparedbytheUnited StatesBureauofReclamation(Mickley,2018)thefivemostcommonlyusedconcentratemanagementalternativesintheUnitedStatesare:(1)surfacewaterdischarge,(2)sewerdisposal,(3)deep-wellinjection,(4)landapplication,and(5) evaporationponds(see Fig.1.3).Thedesalinationconcentratemanagementpracticesshownin Fig.1.3 havesimilarfrequencyofapplicationworldwide.
1.4 Concentratemanagementregulations
Atpresent,therearenofederalregulationsintheUnitedStatesorstateregulations elsewhereintheworldspecificallydevelopedtoaddresswastedischargesfrom desalinationplants(WaterReuseAssociation,2011).Desalinationplantdischarges areclassifiedbytheUnitedStatesEnvironmentalProtectionAgency(USEPA)as industrialwastedespitethefactthatthesedischargesaredistinctivelydifferent frommostindustrialdischarges.SeveralregulatoryprogramsintheUnitedStates thatimpactthedisposalofdesalinationplantdischarges,includingtheCleanWater
Act(CWA),theUndergroundInjectionControl(UIC)Program,ordinancesthat protectgroundwater,andtheResourceRecoveryandConservationAct(RCRA)for anysolidwasteresiduals.Disposaloptionsfordesalinationplantdischargesand associatedregulatoryandpermittingagenciesinclude:
• DisposaltosurfacewaterdischargerequiresaNationalPollutantDischarge EliminationSystem(NPDES)permit.
• Sewerdischargerequiresapermitissuedbythelocalseweragencytomeetits sewerordinanceandtheCWAIndustrialPretreatmentProgram(IPP) requirements,asstipulatedintheagency’sNPDESpermit.
• Concentratedisposalbylandapplication(percolationponds,rapidinfiltration basins,landscapeandcropirrigation,etc.)mustcomplywithfederalandstate regulationstoprotectgroundwater,publichealth,andcrops/vegetation.Land applicationrequiresapermitfromstateagencies.
• Concentratedisposalbydeep-wellinjectionisregulatedbytheUICprogram oftheSafeDrinkingWaterAct.Therelatedconstruction,monitoring,and otherpermitsareissuedandenforcedbytheUSEPAregionorstateagency thathasprimacy.
• RCRAregulatesthedisposalofsolids,suchasprecipitatedsaltsandsludge;if suchsolidscontainarsenicorothertoxinsanddonotpassthetoxic characteristicleachingprocedure(TCLP)test,theyareconsideredahazardous wasteandmustbehandledaccordingly.
FIGURE1.3 Currentconcentratemanagementpractices.
ThemostimportantregulationspertainingtodisposalofdesalinationplantdischargesarethoserelatedtotheCWA,includingtheNPDESprogram.Underthe CWA,desalinationplantdischargesareregulatedasindustrialwastesasthe USEPAhasnotestablishedspecificregulationsconcerningthedisposalofwater treatmentplantresiduals,includingdesalinationplantdischarges.Forsurface waterdischarge,NPDESpermitisrequiredpursuanttotheCWA;itsantidegradationpolicypreventstherelaxationofdischargelimitsforcontaminantsspecified inaNPDESpermit,particularlyifthereceivingwaterisdesignatedassensitive orimpaired.IfawatertreatmentplantcurrentlyhasaTDSdischargelimit,combininghighTDSconcentratefromthedesalinationplantROsystemwiththe existingdischargemaynotbeallowed.
PermittingpracticesintheMiddleEastareverysimilartotheseintheUnited States.TheregulationspertainingtodesalinationplantsinAustralia,Spain,and Israel,whichatpresenthavethelargestnumberofdesalinationplantsoutsideof theMiddleEast,haveanumberofsimilaritiestothoseintheUnitedStates.Inall ofthesecountriesthepermittingprocessforsuchdischargesisthesameasthis appliedforpermittingofdischargesfromwastewatertreatmentplants.Australia hasdischargeregulationsmostsimilarinstructuretotheseintheUnitedStates, wherethefederalgovernmenthasestablishedthebaselinelegalframeworkfor regulationofwastedischargesandtheindividualstateshaveenhancedthefederal regulationswithstateandlocation-specificregulatoryrequirements(Mickleyand Voutchkov,2016).
Despitethesimilarities,thepermittingofmediumandlargesizeprojectsin theUnitedStatesusuallytakeslongerthanthatinAustralia,SpainandIsrael.For example,thepermittingoftheTampaBayandCarlsbadSWROdesalinationprojectswascompletedwithin2.4and5years,respectively.Forcomparison,the averagetimeneededforpermittingofsimilarsizeprojectsinAustraliais1.5 2 yearsandinSpainandIsraelis9 12months.Themainreasonsareasfollows:
• Streamlinedregulatoryprocess:Usuallyonlyoneortwoagenciesareinvolved intheenvironmentalreviewofthedesalinationprojectascomparedtofourto sixagenciesinmostUSstatesandupto24agenciesinCalifornia.
• Priorityreviewofdesalinationprojects:Spain,Israel,andAustraliarecognize thenational/statestrategicimportanceofseawaterdesalinationforsecuring sustainableanddrought-prooflong-termwatersupplyinthesecountries.Asa result,theyhavelong-termplansfordevelopmentandimplementationof desalinationprojects,whichareunderthecloseoversightofthecentral governmentinSpainandIsraelandthestategovernmentinAustralia.Since thetimelyimplementationofsuchplantsisconsideredofhighimportanceand priorityfortherespectivecountries,theregulatoryagenciesaregivensupport atfederallevelinthecaseofSpainandIsrael,andatstatelevelinthecaseof Australiaintermsofexpertise,direction,andfundstoexpediteandgive priorityoftheenvironmentalreviewofdesalinationprojectsascomparedto othertypesofprojects.
• Superiorexpertiseofregulatoryagenciesinpermittingofdesalinationplants:In theUnitedStates,mainlybecauseoffundingconstraints,manyoftheregulatory agenciesinvolvedinthepermittingofdesalinationprojectsusuallydonot maintainstaffwithalltypesofexpertiseneededtocompleteanexpeditedreview ofdesalinationprojectssuchasmarinebiologists,expertsinoutfalldischarge modeling,andengineerswithexperienceinthedesignandoperationof desalinationplants.Forcomparison,thekeyagenciesinvolvedindesalination projectreviewinSpain,Australia,andIsraelhavesuchexpertsonstafforifsuch expertswerenotoriginallyavailable,theywereretainedinexpeditiousmannerat thebeginningoftheprojectreviewtominimizetimeneededforenvironmental projectreview.Forcomparison,mostoftheagenciesinvolvedindesalination reviewinCaliforniadonothavesuchexpertsandasaresulttheenvironmental reviewprocessgoesthrough6 12roundsofrequestsforadditionalinformation bytheregulatoryagencyreviewerssincetheylearnonthejobandwork piecemealontheirquestionsastheylearnmoreabouttheproject.
• Sharingofregulatoryexpertisebetweenvariousagencies:inallofthelisted states,thekeyregulatoryagenciesinvolvedinpermittingofdesalination projectshaveinternalmeetingswheretheyshareexperiencewithvarious permittingissues.Suchregulatorsalsoactivelyparticipateinprofessional conferencesandpublicforumspresentinginclearmannertheirrequirements andexpectationsassociatedwiththetypeanddetailofinformationthatneeds tobesubmittedbytheprojectsponsorsinordertominimizetimeneededfor projectpermitting.Mainlyduetolackoffunds,USregulatorsinvolvedin permittingofdesalinationprojectsusuallydonothavesuchprofessional experienceexchangeopportunitiesinandoutofstateandrarelyattend professionalconferencesorpresenttheirexpectationsinprofessionalforums.
Inallcountriesreferencedearlier,thedesalinationplantpermitsareissued afterathoroughenvironmentalreviewoftheimpactoftheplantdischargeonthe surroundingaquaticenvironment,whichisdeterminedbasedon
• Projectionsofconcentratewaterqualitydevelopedbasedonsourceseawater qualitycharacterizationandthespecificdesignfeaturesofthedesalination plant(plantrecovery,productwaterquality,typeofintake,anddischarge).
• Biologicalsurveyofthedischargeareaaimingtodocumentthetypeand quantityofmarinespeciesinhabitingthisareaandtheirsalinitytolerance.
• Inallofthereferencedcountriesthesalinitytoleranceofmarineorganismsis determinedbasedonchronic(orinthecaseofsomeAustralianstates),acute wholeeffluenttoxicity(WET)testingofthemostsensitivespeciesinhabiting thedischargearea.InAustraliathemarineorganismsaretestedinembryonic stageofdevelopment,whichhasresultedinthemoststringentrequirements forconcentratedilutionascomparedtotheseinSpainandIsraelwherethe testspeciesusedfordeterminingsalinitytoleranceareinadultphase.
• Themixingrequirementsforthedesalinationprojectsaredeterminedbasedon theWETtestingstudyandhydrodynamicmodelingofthedischargearea.
InSpainandIsraelusuallyonlyoneenvironmentalregulatoryagencyhasthe righttomakedecisionsandestablishdischargepermitrequirementsandmitigationmeasures.Ifotheragenciesareinvolvedintheprojectreview,theyprovide commentstotheleadagencybuthavenorightorjurisdictiontochangepermittingrequirementsexceptbyinternalconsensus.InAustralia,keydecisionsare madeatstatelevelbyoneleadagency.Forcomparison,theindependentmultiagencyreviewprocesstypicalforstatessuchasCaliforniaresultsinnumerous conditionsandpermitswhichregulatethedischargeandwhichmayhavedifferentrequirementsintermsofmitigationofenvironmentalimpacts.Suchpractices notonlydelaythepermittingprocessbutalsoputasignificantburdenontheprojectsponsorassociatedwithprojectimplementation,operationsmonitoringand datareporting.
Regulationsapplicabletosurfacewaterdischargeacrosstheworldare expandedoninChapter3,SurfaceWaterDischargeofConcentrate.
References
Mickley,M.C.,2018.UpdatedandExtendedSurveyofU.S.MunicipalDesalination Plants.DesalinationandWaterPurificationResearchandDevelopmentProgram ReportNo.207.Denver:USBureauofReclamation.
Mickley,M.C.,Voutchkov,N.,2016.Databaseofpermittingpracticesforseawaterconcentratedisposal.WaterEnviron.ReuseRes.Found.
Jones,E.,Qadir,M.,vanVliet,M.T.H.,Smakhtin,V.,Kang,S.,2018.Thestateofdesalinationandbrineproduction:aglobaloutlook.Sci.TotalEnviron.657,1343 1356. WaterReuseAssociation,2011.SeawaterConcentrateManagement,WhitePaper.WRA, Alexandria,VA.
2
2.1 Desalinationplantwastestreams
Mostmembranedesalinationplantshavethefollowingcomponents,whichare shownin Fig.2.1:
• apointofintaketocollectsalinesourcewater(ground-orseawater);
• atypeofpretreatmentsystemwiththemainpurposeofremovingsuspended solids,organics,andscalingmineralsfromthesalinesourcewater;
• asystemofreverseosmosis(RO)membranesandequipmentwhichprocess thesourcewatertoproducefresh,lowsalinitywater(calledpermeate)by separatingdissolvedsolidsfromthepretreatedsalinewater;and
• aposttreatmentsystemtoaddbacknecessarymineralstotheproductwaterto makeitsuitablefordistributionandfinaluse.
Brackishwaterdesalinationplantsincludemostofthesamekeytreatment processcomponentsasseawaterdesalinationfacilities.However,inmanybrackishplants,aportionofthesourcewaterisbypassedandblendedwithplantpermeatetoachievetargetwaterquality.
Desalinationplantresidualstypicallyinclude:
• ConcentrategeneratedbytheROsystem,whichcontainsdissolvedand particulatecontaminantsremovedfromthefeedwater.Concentratemayalso containchemicalsfromthesourcewaterconditioningandthepretreatment facilities.
• Spentfilterbackwashwatergeneratedbythedesalinationplantpretreatment system.
• Spentcleaningsolutionsfromtheperiodicchemicallyenhancedcleaningof theROandpretreatmentmembranes(ifmembranepretreatmentisused). Thesewastestreamscontainahighconcentrationofthecleaningchemicals, alongwiththefeedwatercontaminantsremovedduringmembranecleaning.
Desalinationplantsareusuallydesignedtooperateandproducepermeatecontinuously.Concentrateisgeneratedasabyproductwhenevertheplantis
Schematicoftypicalmembranedesalinationplant.
operational.Thevolumeandfrequencyofbackwashwatergeneratedisdependent onthetypeofpretreatmentsystem;granularmediafiltershavebackwashcycles withdurationof24 48hours,whilemembranepretreatmentsystemshavecycles farshorter,typicallybetween30and60minutes.Spentcleaningsolutionsgeneratefarsmallervolumesofdischarge,dependingontherequiredfrequencyofRO membranecleaningwhileside-streamsfrompretreatmentmembraneclean-inplace(CIP)cleaningareusuallygeneratedmonthlyoronceeveryseveralmonths (Voutchkov,2011a).
TheROandpretreatmentmembranesaretypicallycleanedwithacid(mineral orcitric)toremoveinorganicfoulantsandwithalkalinesolutions(i.e.,sodium hydroxide,oftenincombinationwithdetergents/surfactantsandsometimeswith chelatingagents)toloosen,dislodge,andremovebiofilmsandorganicfoulants. Sodiumhypochloriteisalsoappliedforperiodic(onceperdaytoonceperweek) enhancedbackwashofthepretreatmentmembranestocontrolexcessivebiogrowthonthemembranefibers.
2.2 Concentrate
Separatingmineralsandcontaminantsfromsourcewaterresultsintwoliquid streams:onewithamuchreducedconcentrationofminerals(freshwater),the otherwithfarhigherconcentration.Thestreamwithhighersalinityconcentration thatcontainsthemineralsremovedfromthesourcewaterisknownas“concentrate.”Theconcentratealsocontainstheantiscalingchemicalsaddedduringthe sourcewaterconditioningprocesspriordesalination.
FIGURE2.1
2.2.1 Quantity
Thevolumeofconcentratedependsonthesizeofthedesalinationplantandon theratiobetweentheproducedfreshwaterandthesalinesourcewatercollected foritsproduction.Thisratioistypicallyreferredtoasarecoveryrateand expressedinpercentofthecollectedsourcewater.Desalinationplantsareclassifiedintermsofthevolumeoffreshwatertheyproduce,wheresmallplantsare consideredfacilitiesthatyieldlessthan20MLDwhilelargeplantsproducehundredsofmillionsoflitersperday.Therecoveryratesdifferdependingonthe typeofplantandotheroperationalconditions:mostseawaterROplantstypically haverecoveryratesbetween40%and55%whilebrackishwaterdesalination plantsoperateatsignificantlyhigherrecoveryof65% 85%(Voutchkov,2011a).
Therecoveryrateofaplant(R )issimplytheratioofthevolumeoffresh waterproduced( Qp )dividedbythevolumeofsalinesourcewater(Q s)collectedforproductionofthisfreshwater.Thevolumeofconcentrateproduced ( Qc )isthedifferencebetween Qs and Qp .Asdesalinationplantsareclassified intermsofthevolumeoffreshwaterp roducedandtherecoveryratherthan thevolumeofsourcewaterrequired,thevolumeofconcentratecanbecalculatedas(Voutchkov,2011a):
Example
Foralargeseawaterdesalinationplantoffreshwaterproductioncapacityof100MLDoperating atarateofrecoveryof45%,thedailyconcentratevolumeiscalculatedasfollows:
Qc seawaterplant 5 100; 000m3 =day 3 1
=day
Withthesamefreshwaterproductioncapacityof100MLD,abrackishwaterdesalination plantdesignedatrecoveryrateof80%willgeneratenearlyfivetimeslessconcentratethanthe seawaterplant:
Qc brackishwaterplant 5 100; 000m3 =day 3 1 0 80 ðÞ=0 80 5 25; 000m3 =day
2.2.2 Quality
Thequalityofconcentrateismainlyafunctionofthecompositionofthesource water,andisinfluencedbytherecoveryrate.Thehighertherecoveryrate,the highertheconcentrationofmineralswillbeintheconcentrate. Witharecoveryratebetween65%and85%,thesalinityofbrackishplant concentratecanbebetween4and10timeshigherthanthatofthesalinesource water.Thefarlowerrecoveryofseawaterplantsresultinconcentrateofbetween
