PhosphorusrecoveryfromdigestedsewagesludgeasMAPbyt

PhosphorusrecoveryfromdigestedsewagesludgeasMAPbythehelpofmetalionseparationKenanGu¨ney*,AlexanderWeidelener,Jo¨rgKrampeStuttgartUniversity,InstituteforSanitaryEngineering,WaterQualityandSolidWasteManagement,Bandta¨le2,70569Stuttgart,GermanyarticleinfoArticlehistory:Received25February2008Receivedinrevisedform11June2008Accepted13August2008Publishedonline27August2008Keywords:MAPStruvitePhosphorusrecoveryMetalionseparationNafion117DonnanprocessCationexchangeFertilizerDigestedsewagesludgeabstractThisstudywasdesignedtosolvemetalioninfluenceproblemonphosphorusrecoveryfromdigestedsewagesludgeasMAP.TheexperimentalstepswereproceededtomaximizeMAPproductionanditsquality.Usedexperimentalstepswere:(a)Acidicdissolutionofphosphorus,(b)Removalofmetalionsfromphosphorusrichwaterphase,(c)RecoveryofphosphorusasMAP,(d)SeparationofMAP.AlldigestedsewagesludgesamplesweretakenfromStuttgartUniversitysewagetreatmentplantforresearchandeducation(LFKW).FourdifferentformsofLFKWdigestedsewagesludgewereusedasfeedingsample.Thesewere:originaldigestedsludge,diluteddigestedsludge,centrifugeddigestedsludgeandincinerateddigestedsludge.ADonnanmembraneunithavingaNafion117(DuPont)cationexchangemembranewasusedtoremovemetalionsfromthesamplesused.Highestmetalionremovalefficiencies,whichwere98%,97%,and80%forAl,CaandFeions,respectively,wereobtainedfromincinerateddigestedsludgerun.IncinerateddigestedsludgerunwasusedaspreliminarystepforMAPproductionandhighqualityMAPwasproduced.ProducedMAPfulfilsallrequirementsrelatedwithDu¨ng-emittelverordnung2003anditcouldbeusedasafertilizerinGermany.ª2008ElsevierLtd.Allrightsreserved.1.IntroductionPhosphorusisanessentialnutrientforallformsoflife.Phosphorusconsumptionintheworldinyear2006wasaround142milliontonsofphosphaterockconcentrate(U.S.GeologicalSurvey,2008),whichisannihilatingeconomicallyextractablephosphaterocks.Therefore,therelianceonphosphaterocksshouldbestoppedandsustainablewaystousephosphorusshouldberesearched.Asustainablewaytousephosphoruscanberecoveryofphosphorusfromdigestedsewagesludge(willbereferredasdigestedsludge)sincealmostalltheremovedphosphorusaccumulatesintreatmentsludgeinaconventionalwaste-watertreatmentplantwhetherphosphorusinwastewaterisremovedbybiologicalphosphorusremovalorbychemicalphosphorusremoval.Ontheotherhandmostofthemetalionsandheavymetalsaccumulateintreatmentsludgetoo.Al,CaandFe(mainmetals)ionconcentrationsindigestedsludge*Correspondingauthor.Fax:þ49(0)71168563729.E-mailaddresses:[e-mail](K.Gu¨ney),[e-mail](A.Weidelener),[e-mail](J.Krampe).Availableat–seefrontmatterª2008ElsevierLtd.Allrightsreserved.doi:10.1016/j.watres.2008.08.016waterresearch42(2008)4692–4698areusuallyhigh,especiallywherephosphorusremovalismadebyadditionofmetalsalts.Sincemineralfertilizersaccountforapproximately80%ofphosphatesusedworldwide(Steen,1998),itwouldbebenefi-ciarytorecoverphosphorusfromdigestedsludgeasafertil-izer.Oneofthemostpopularphosphorusrecoveryapplicationsinthissenseisconvertingphosphorusfromdigestedsludgeintomagnesiumammoniumphosphatehexahydrate(MAPorstruvite).MAPisaslowreleasingfertilizerwithachemicalformulaofMgNH4PO4$6H2O.ThequalityofMAPasafertilizerhasbeenresearchedandusuallyfoundasinaveragetohighquality(Ahmedetal.,2006;Ghoshetal.,1996;ScopeNewsletter,2001).MinimumMAPsolubilityisobservedbetweenpH8.0andpH10.0(Buchananetal.,1994;Bookeretal.,1999;MombergandOellermann,1992).DuringpHarrangementofdigestedsludgesamplesforMAPproduction,mainmetalionsreactwithavailablephosphorusandprecipitateasmetalphos-phatesatpHabove4.0(Jafferetal.,2002;Weideleneretal.,2005),reducingphosphorusconcentrationwhichisavailabletoformMAP.Therefore,topreventthere-precipitationofphosphoruswithmetalions,interferingmetalionshavetobeeitherremovedorinactivated.Weideleneretal.(2005)investigatedthehandlingofmainmetalionsfromdigestedsludgeofStuttgartUniversitysewagetreatmentplantforresearchandeducation(Lehr-undForschungskla¨rwerkBu¨snau-LFKW)toincreaserecoveryofphosphorusasMAP,byusingcomplexingagents.Buttheyfoundthat,despitetheapplicationofcomplexingprocess,MAPproductionefficiencywasaffectednegativelybyhighconcentrationofaluminium.Prakashetal.(2004)investigatedremovalofAlfromwatertreatmentplantresidualsbyusingDonnanmembraneprocesswhichincludesaNafion117(DuPont)cationexchangemembraneandobserved81%Alremoval.Schaum(2007)usedDonnanmembraneprocesswhichincludesaNafion(DuPont)cationexchangemembranetoremoveAlionsoutofAlPO4solutionwhichhas8gP/l.Heobservedalmost60%Alremovalandalmost14%Premovalin16hofmembraneunitopera-tion.ThereforeusingaDonnanmembraneprocesstoremovemetalionsbythehelpofaNafion117membranewasthoughttobeapromisingidea.ThisresearchwasfocusedonmetalionremovalpriortoMAPproduction.LFKWdigestedsludgesampleswereusedindifferentformstorecoverphosphorusasMAP.First,thebestmetalionremovalmethodwasinvestigatedandthenMAPproductionwasprocessedbyusingitaspreliminarystep.Asfinalstep,usabilityofproducedMAPasafe