Phosphorus-recovery-by

PhosphorusrecoverybystruvitecrystallizationinWWTPs:InfluenceofthesludgetreatmentlineoperationN.Martı´a,L.Pastorb,A.Bouzasa,*,J.Ferrerb,A.SecoaaDpto.Ingenierı´aQuı´mica,UniversidaddeValencia,DoctorMoliner50,46100Burjassot,Valencia,SpainbInstitutodeIngenierı´adelAguayMedioAmbiente(IIAMA),UniversidadPolite´cnicadeValencia,CaminodeVera,s/n46022Valencia,SpainarticleinfoArticlehistory:Received23July2009Receivedinrevisedform15December2009Accepted28December2009Availableonline7January2010Keywords:CrystallizationPhosphorusrecoverySludgetreatmentStruviteWastewaterabstractPhosphorusrecoverybystruvite(MgNH4PO4$6H2O)crystallizationisoneofthemostwidelyrecommendedtechnologiesfortreatingsludgedigesterliquorsespeciallyinwastewatertreatmentsplants(WWTP)withenhancedbiologicalphosphorusremoval(EBPR).Inthispaper,phosphorusrecoverybystruvitecrystallizationisassessedusingtherejectedliquorsresultingfromfourdifferentoperationalstrategiesofthesludgetreatmentline.Phosphorusprecipitationandrecoveryefficienciesofbetween80–90%and70–85%,respectively,wereachievedinthefourexperiments.Theprecipitatesformedweremainlystruvite,followedbyamorphouscalciumphosphateand,insomeexperiments,bycalcite.Thehighestglobalphosphorusrecoverytakingintoaccountboththesludgelineandthecrystallizerwasachievedwhenmixedthickeningandhighelutriationwerecarriedout(8.4gP/kgtreatedsludge).However,lowstruvitecontentwasobtainedinthecrystallizerwiththisoperationschemeduetothehighcalciumcontentintheelutriationstream.Therefore,ifthefinalpurposeistoobtainstruvite,thereductionoftheelutriationflowrateiswidelyrecommendedinthecaseofhighwaterhardness.ª2010ElsevierLtd.Allrightsreserved.1.IntroductionPhosphorusrecoverybystruvite(MgNH4PO4$6H2O-MAP)crystallizationisoneofthemostwidelyrecommendedtech-nologiesfortreatingsludgedigesterliquors(vonMu¨nchetal.,2001;Battistonietal.,2002;ParsonsandDoyle,2004)especiallyinwastewatertreatmentsplants(WWTP)withenhancedbiologicalphosphorusremoval(EBPR).IntheEBPRprocess,phosphatesandotherions(i.e.,Mg2þ,K2þ)aret