ReviewPhosphorusremovalandrecoverytechnologies

.TheScienceoftheTotalEnvironment212199869]81Review:PhosphorusremovalandrecoverytechnologiesG.K.Morse,S.W.Brett,J.A.Guy,J.N.LesterUImperialCollegeCentreforEn¨ironmentalTechnology,En¨ironmentandWaterTechnologyGroup,48PrincesGardens,LondonSW72PE,UKReceived24October1997;accepted26November1997AbstractAreviewhasbeenundertakenoftechnologiestoremoveandrecoverphosphorusfromwastewaterandtheirpotentialtofacilitatetherecyclingofphosphorusanditssustainability.Awiderangeoftechnologieswereidentified,includingchemicalprecipitation,biologicalphosphorusremoval,crystallisation,novelchemicalprecipitationap-proachesandanumberofwastewaterandsludge-basedmethods.Phosphorusinwastewaterrepresentsasignificantrenewableresourceandthereisnoenvironmentalortechnicalreasonwhyphosphoruscannotberecycled.Indeed,therearemanypotentialenvironmentalbenefitsfromreducingrelianceonphosphaterockandassociatedimpurities,apracticewhichisultimatelyunsustainable.Co-operationandleadershipbygovernmentisrequiredtoprogressphosphorustowardssustainability.Q1998ElsevierScienceB.V.Keywords:Phosphorusremoval;Sustainability;Phosphateindustry;Crystallisation1.IntroductionSustainabilityisanimportantenvironmentalconcernincreasinglyreflectedincorporatestrat-egy,governmentalpolicyandinternationalagree-ments,suchastheRioSummitAgenda21United.Nations,1993.Phosphorusisanimportantele-UCorrespondingauthor.Tel.:q441715946020;fax:q441715946016;e-mail:[e-mail],makingamajorcontributiontoagriculturalandindustrialdevelopment.However,itsreleasetosurfacewatersinagriculturalrunoffandwastewatershasledtolegislation,suchastheEuropeanUnionUrbanWastewaterDirectiveCommissionoftheEuropeanCommunities,.1991,designedtoremovephosphorusfromdo-mesticandindustrialwastewater.Thedevelopmentoftechnologyforphosphorusremovalofferstheopportunityforrecyclingandphosphorussustainability.However,therearea0048-9697r98r$19.00Q1998ElsevierScienceB.V.Allrightsreserved..PIIS0048-96979800332-X()G.K.Morseetal.rTheScienceoftheTotalEn¨ironment212199869]8170numberoftechnologies,bothestablishedandun-derdevelopment,whichcanbeusedtoremovephosphorusfromwastewaterandcanpotentiallybeusedwithinasustainabilitystrategy.Thisarticleisthereforeacomprehensivere-viewoftechnologiesthatremoveandrecoverphosphorusfromwastewaterandanevaluationoftheirapplicabilitytophosphorussustainability.Informationforthestudyhasbeendrawnfromanextensivereviewofawiderangeofliterature,includingpatentsearches,complementedbycon-tactwithexpertsthroughouttheworld.Thestudycoversalltechnologies,fromthoseestablishedandinuse,throughtothosewhicharestillrela-tivelynewideasandresearchprojects.2.PhosphorusremovaltechnologiesDevelopmentoftechnologiesforphosphorusremovalstartedinthe1950sinresponsetotheissueofeutrophicationandtheneedtoreducethelevelsofphosphorusenteringsurfacewaters.Removalwasinitiallyachievedbychemicalpre-cipitation,whichremainstheleadingtechnologytoday.Morerecentlyhowever,biologicalphos-phorusremovalhasbecomefirmlyestablished,crystallisationtechnologyhasalsocompleteditsprogresstowardscommercialisationandtech-nologiesextendingchemicalprecipitationtoassistnutrientremovalarebeyondthepilotstage.Otherrelevanttechnologiesareatvariousstagesofde-velopmentorhavebeeninvestigated.Asummaryofthevarioustechnologiesispro-videdinTables1]3.GeneraldevelopmentandstatusofalltechnologiesidentifiedissummarisedinTable1,whiletheprocessdetailsofthemaingenerictechnologiesarepresentedinTable2.AnassessmentoftheirapplicationinwastewatertreatmentisprovidedinTable3.Thetechnolo-giesarereviewedinmoredetailbelow.2.1.ChemicalprecipitationThewidespreaduseofchemicalprecipitationforphosphorusremovalinwastewatertreatmentstartedinSwitzerlandduringthe1950s,inre-sponsetothegrowingproblemofeutrophication.Thissimpletechnologyisnowfirmlyestablishedinmanycountriesaroundtheworld.Chemicalprecipitationisinessenceaphysico]chemicalprocess,comprisingtheaddi-tionofadivalentortrivalentmetalsalttowastewater,causingprecipitationofaninsolublemetalphosphatethatissettledoutbysedimenta-tion.Themostsuitablemetalsareironandaluminium,addedaschloridesorsulphates.Limemayalsobeusedtoprecipitatecalciumphos-phate.Anionicpolymersmaybeusedtoassistsolidseparation.Chemicalprecipitationisaveryflexibleap-proachtophosphorusremovalandcanbeappliedatseveralstagesduringwastewatertreatmentFig..1.Primaryprecipitationiswherethechemicalisdosedbeforeprimarysedimentationandphos-phorusremovedinprimarysludge.Secondaryor.simultaneousprecipitationiswherethechemicalisdoseddirectlytotheaerationtankofanacti-vatedsludgeprocessandphosphateremovedinsecondarysludge.Tertiarytreatmentiswheredosingfollowssecondarytreatmentandalthoughahigh-qualityeffluentcanbeproduced,thisap-proachisnotgenerallyfavouredbecauseofhighchemicalcostsandthecreationofanadditional,chemical,tertiarysludge.Chemicalprecipitationtypicallyproducesphos-phorusboundasametalsaltwithinthewastedsludge.Whendisposedtoagriculture,itthereforehaspotentialvalue,althoughresearchonbioavailabilityisinconclusiveYeomanetal.,.1988.Thisuncertaintyhascontributedtothedesiretodevelopalter