Water Quality Analysis of Reverse Osmosis Desalination Brine

Hu Haiyan　Zhou Lin

Abstract：Seawaterdesalinationdevelopsfastasasignificantmethodtosolvetheglobalwaterresourcecrisis.Buttherearerarereportaboutthequalityofconcentratedseawater.Inthispaper，manyparametersofseawaterdesalinationwaterandoriginalseawaterareanalyzed.thedatawegotmaybesomethingusefulforthewaterenvironmentmanagementandscientificstudy.

Keywords：Seawaterdesalination；concentratedseawater；waterqualityanalysis

Introduction

Desalinationisanadvancednewtechnologyofcreatingwaterandsavingwaterwhichisparticularlyappliedtotheislandenvironment.IthasbeenextendedandappliedtotheworldandChinascoastalareaswidelybecausethatitcanalleviatethelackoffreshwaterresourceseffectively.Bytheendof2008，thewaterproductioncapacityofthedesalinationprojectsbuiltinChinareached190，000tonsperday.Andthewaterproductivityrosebyarateof15%-25%peryear.Thesalinityoftheconcentratedseawatergeneratedduringtheoperatingofthedesalinationprojectsishigh.Andtheconcentratedseawatercontains chemicalagentandreactionproductsaddedinthehandlingprocess.Itwillcauseseriousimpactontheenvironmentifwedoemissionwithoutdisposing.Atthesametime，itwillbeawasteofhighconcentratedchemicalresources.Aimingatthereverseosmosisdesalinationtechnologywhichismostwidelyusedinourcountry，inthispaperwetaketheconcentratedseawaterdischargedfromthereverseosmosisdesalinationastheresearchobject，analyzethemainchemicalparameters，andsumupthephysicalandchemicalpropertiesaswellasthereasonscausingitscharacteristics.Theresultswillhaveimportantreferencesignificanceforthehealthydevelopmentofthedesalinationindustry.

1Materialsandmethods

1.1Theoriginalseawaterandconcentratedseawateroftheexperiment

Inthisexperiment，weuseconcentratedseawaterofdesalinationplantofDaishancounty，Zhoushancity.Theoriginalseawaterisfromtheseaareanearthedesalinationplant.

1.2Theanalysismethodoftheexperiment

Asfortheanalysismethod，wetakethespecificationofmarinemonitoringGB17378.4-2007asareference.

2.Theresultandanalysisoftheexperiment

AccordingtotheseawateranalysisofPart4ofspecificationofmarinemonitoringGB17378.4-2007，wemakedataanalysisanderrorcorrectionof20seawatersamplesoforiginalseawaterandconcentratedseawaterandthengettheaverageoftheparametersinTab.1.

ThedataoftheoriginalseawaterandconcentratedseawaterobtainedbyPHnotationisshowninTable1.ItcanbeseenthatthePHoftheconcentratedseawaterafterdesalinationdoesntchangemuchcomparedwiththePHofconcentratedseawaterbeforedesalination.Itsslightlylower.ThedataoftheoriginalseawaterandconcentratedseawaterobtainedbyiodometryisalsoshowninTable1.Thedataprovesthattheoxygencontentdissolvedinthewaterthroughthedesalinationisslightlyimproved.ThepossiblereasonwasthatoxygenwentintotheconcentratedseawaterduringtheprocessoftransportationbecausethatIfoundthattheconcentratedseawaterwasexposedagainintheair，ratherthaninaclosedpipelinewhengettingwaterfromthedesalinationplantinDaishan.AscanbeseenfromthedatainTable1，Thesalinity，Ca，MgandSO42-inconcentratedseawaterareabouttwiceofthemintheoriginalseawater，whichexplainsthatthesematerialsarenotremovedfromtheprocessofdesalination.Thedrinkingwaterdoesntcontaintheabovematerialssubstantiallyafterthedesalting.Andtherateofdesalinatedwaterandconcentratedseawateris1：1.Sonaturallythematerialsintheconcentratedseawaterwillbetwicethecontentsintheoriginalseawater.Therefore，theconcentratedseawatercontainshighconcentratedCa，Mg，andSO42-.ComparedwiththeCOD、PO43-andNO2- intheoriginalseawater，thecontentsofCOD、PO43-andNO2-intheconcentratedseawaterdecreasesignificantly.Thedeclineoftheabovedatacanprovethatthedesalinationremovesmostofthecreaturesandmicrobes.Therefore，thenutrientsaltsintheconcentratedseawateraremuchlowerthanthenutrientsaltsintheoriginalseawater.FromthedatainTable1，wecanclearlyseethatthematerialsofHg，AsandPbarenottested，whichprovesthatthedesalinationrecoversthispartofheavymetalelements.Itreflectsthatthedesalinationcangreatlyreducethecontentofheavymetalsintheoceanfromtheside.

3.Prospect

Thefactorsthataffectthenatureofstrongbrineincludethequalityofthefeedwater，desalinationprocess，therecoveryrate，chemicaladditivesusedinpre-processingandpost-processing.Thecompositionofthestrongbrineismainlyaffectedbytwoparts.Oneisthehighconcentratedsaltobtainedbytheconcentrationoffeedwaterthroughdesalinationprocess.Theotheristheinfluenceofthechemicalsaddedinthepretreatmentprocesstothemembranedesalination（mainlythereverseosmosis）.Thepretreatmentofseawaterincludestheoperationofdisinfection，flocculation，pHadjusting，addingtheantifoulingagentandsoon.Thedistillationdesalinationusuallyneedstoaddedacidorscaleinhibitionagenttopreventfoulinginthedesalinationprocess.ItalsorequiresaddingbasetoadjustthevalueofpH.Thechlorocidebiologyisalsorequiredtobeadded.Thesechemicalsandthehighconcentratedsaltoftendischargetogetherwiththestrongbrine，whichmayhavenegativeimpactontheenvironmentoftheemissionwaterareas.

Butthemainpropertyofthestrongbrineisnotdecidedbythechemicalsaddedintheprocessbecausetheconcentrationoftheaddedchemicalsisrelativelylow（generallylessthan10mg/L）.Thenatureofthestrongbrineismainlydecidedbythecompositionexistedintherawwater.Whentheconcentratedrecoveryofthestrongbrineis50%，theconcentrationofthestrongbrinedischargedfromthereverseosmosisdesalinationistwicetheconcentrationofthenaturalseawater.Whenthestrongbrineofthedistillationdesalinationdischargestogetherwiththerefrigeratedseawater，theconcentrationoftheemissionwaterisapproximate10%-15%higherthantheconcentrationoftheseawater.

Acknowlegements

Thisworkwassupportedby2010s“StudyontheproductionofMFFwithdesalinationbrineandoptimizationofitscraft”（No.2010C33055）fromProjectofZhejiangScienceandTecnologyBureau，and2009s“DesalinationwithCarbonnanotube”fromProjectofZhejiangOceanUniversity（No.21105030609）.

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