Aneconomicevaluationofphosphorusrecoveryasstruvite

ReviewPaperAneconomicevaluationofphosphorusrecoveryasstruvitefromdigestersupernatantL.Shua,P.Schneidera,V.Jegatheesana,*,J.JohnsonbaSchoolofEngineering,JamesCookUniversity,Townsville,Qld4811,AustraliabGreatBarrierReefMarineParkAuthority,Townsville,Qld4810,AustraliaReceived29July2005;receivedinrevisedform2November2005;accepted5November2005Availableonline20December2005AbstractPhosphoruscanberecoveredfromwastewaterthroughcrystallisationofstruvite,MgNH4PO4Æ6H2O.Approximately1kgofstruvitecanbecrystallisedfrom100m3ofwastewater.Crystallisationisprofitablecomparedtochemicalandbiologicalremovalofphosphorusduetosavingsfromthereductionin(i)chemicalsusedforprecipitationandsludgedisposal;and(ii)downtimeforcleaningunwantedstruviteformedduringchemicalandbiologicalremoval.Thestruviteproducedannuallyfromawastewatertreatmentplantthatpro-cessed100m3/d,wouldbesufficienttoapplyon2.6haofarableland,asfertilizer.Ifstruviteweretoberecoveredfromwastewatertreat-mentplantsworldwide,0.63milliontonsofphosphorus(asP2O5)couldbeharvestedannually,reducingphosphaterockminingby1.6%.Therefore,thistechnologycouldprovideopportunitiestorecoverphosphorussustainablyfromwastestreamsandpreservephosphorusreserves.2005ElsevierLtd.Allrightsreserved.Keywords:Crystallisation;Phosphorusrecovery;Struvite;Sustainability;Wastewatertreatmentplant1.IntroductionPhosphorus(P)isoffundamentalimportancetolivingthings,includinghumanswhodependonphosphorustoleadhealthyandproductivelives,andasanessentialnutrientforcropproduction.Furthermore,thereisnosubstituteforphosphorusinnature(USGS,2005).Itisestimatedthatthereare7000milliontonsofphosphaterocksasP2O5remaininginreservesthatcouldbeeconom-icallymined.Thehumanpopulationconsumes40mil-liontonsofPasP2O5eachyear(FloridaInstituteofPhosphateResearch,2005;Steen,1998;Jasinskietal.,1999).ItispredictedthatPdemandwillincreaseby1.5%eachyear(Steen,1998).Estimatesarethattheresourcecouldbeexhaustedinaslittleas100–250years(EuropeanFertilizerManufacturersAssociation,2000).Thereare11000milliontonsofphosphaterocksthatcannotbeprocessedeconomicallyatpresent.Evenifthesereservescouldbeprocessedeconomicallyinthefuture,theyarenotarenewableresourceandtherefore,recoveringphos-phorusfromwastestreamsisasignificantbreakthroughtechnology.Reducingphosphorusreleasedinwastewaterhasim-portantenvironmentalimplications,asthephosphorusreleasedintowaterbodiesfromwastewatertreatmentplantscanhavearangeofeffects,includingalgalblooms,whichreducelightpenetrationandavailableoxygeninthewaterbody.Algalbloomsoccurringnearcoralreefscanaffectcoralsbypreventingthepenetrationofsunlight,whichisessentialforthecoralgrowth.Excessivephos-phorusalsoweakenscoralskeletonmakingcoralsmoresusceptibletophysicaldamage.Australia’sGreatBarrierReef(GBR)stretches2500kmalongthenortheastcoastofQueenslandandisanareaofhighbiologicaldiversity,economicvalueandsocialandculturalimportance.AsaWorldHeritageproperty,theGBRattractsmillionsof0960-8524/$-seefrontmatter2005ElsevierLtd.Allrightsreserved.doi:10.1016/j.biortech.2005.11.005*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](V.Jegatheesan).BioresourceTechnology97(2006)2211–2216touristseachyearwithitspicturesquescenery,clearwatersanddivingrelatedactivities.TheGBRcontributesAUD$5.1billiontotheAustralianeconomyfromtourism,andgeneratessubstantialeconomicvaluefromrecreationalandcommercialfishing(CRCReef,2005;GreatBarrierReefMarineParkAuthority,2004).Currently,thereare35wastewatertreatmentplants(WWTP)beingoperatedon28islandsintheGreatBarrierReefWorldHeritageArea.ThecapacitiesofthoseWWTPsrangefrom100to1000m3/d.TheseWWTPs,togetherwithWWTPsonthemainlandintheGBRcatchment,treatatotalof60millioncubicmetersofwastewaterannually(Schneider,2004).ManagementofWWTPsintheGreatBarrierReefWorldHeritageAreaisjointlyundertakenbytheGBRMPAandQueenslandEnvironmentalProtectionAgency(Water-houseandJohnson,2002;Brodie,1995).Aload-basedapproachhasbeenimplementedtoregulatewastewaterdischargesintotheGreatBarrierReefMarinePark,andmanyoftheresortsareupgradingtheirWWTPscapabili-tiesandeffluentreuseinfrastructuretomeetthesestan-dards(SewagedischargesfrommarineoutfallstoGreatBarrierReefMarinePark,2005).Themostcommonmethodforphosphorusremoval(whichisoneofthenutri-entsalongwithnitrogenthataretargetedinwastewaterdischarge)ischemicalprecipitationandenhancedbiologi-calphosphorusremoval(Lesjeanetal.,2003;MombergandOellermann,1992;Winteretal.,1992).Chemicalpre-cipitationincreasessludgevolumeanddecreasesthebio-degradabilityofthesludge,andthegeneratedsludgeisexpensivetodisposeof.Therefore,theeconomicfeasibilityofcrystallisingstruvite(MgNH4PO4Æ6H2O)fromanaero-bicdigestersofthereefboundwastewaterhasbeeninves-tigatedinthisstudy.Thiswillnotonlyhelptomeetpolicyrequirements,butwillalsohelptorecoverphospho-rusasstruvite,whichcanbeappliedasafertiliser.StruvitegenerationwillalsoreducethechemicalcostsassociatedwithaWWTPasitwillreducesludgegeneration(duetochemicalprecipitationofphosphorus)anddecreasethelandfillareathatwillberequiredforsludgedisposal.Researchsh