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ProcessBiochemistry40(2005)723–732Comparisonbetweenacclimatedandunacclimatedbiomassaffectinganaerobic–aerobictransformationsinthebiologicalremovalofphosphorusYinguangChena,∗,Yin-ShengChenb,QingXua,QiZhoua,GuoweiGuaaNationalKeyLaboratoryofPollutionControlandResourcesReuse,SchoolofEnvironmentalScienceandEngineering,TongjiUniversity,Shanghai200092,PRChinabUNILABResearchCenterofChemicalReactionEngineering,EastChinaUniversityofScienceandTechnology,Shanghai200237,PRChinaReceived15July2003;accepted31January2004AbstractAcclimatedandunacclimatedexperimentswereconductedwithpropionic/aceticacidswastewaterandactivatedsludge(biomass)long-termcultured,respectively,withaceticandpropionicacidenrichedwastewater.Biomassacclimatedwiththepropionicacidenrichedwastewater,comparedwithunacclimated,hadaincreasedspecificsolubleortho-phosphate(SOP)release(increasedfrom0.75to0.91mmol-P/g-MLVSS)anduptake(from0.96to1.25mmol-P/g-MLVSS),SOP-uptake/SOP-releaseratio(from1.28to1.38mol/mol),netSOPremoval(from0.46to0.69mmol/l)andSOPremovalefficiency(from61.33to92.00%).However,theratiosofbothanaerobicaccumulatedandaerobicutilisedpolyhydroxyalkanoates(PHA)werereduced.Thereasonsforthesechangeswereduetothedecreasedglycogentransformationsandcellgrowthaswellasincreasedphosphorusaccumulatingorganisms(PAO)involvedintheacclimatedbiomass.Furtherinvestigationindicatesthatthepropionicacidenrichedwastewaterwaslessefficientforenhancedbiologicalphosphorusremoval(EBPR)thanaceticacidinshort-termtests,butmuchmoreefficientinthelong-termculturedexperiments.©2004ElsevierLtd.Allrightsreserved.Keywords:Phosphorusbiologicalremoval;Acclimatisation;Activatedsludge;Propionic/aceticacid1.IntroductionRecently,interesthasdevelopedintheuseofbiological,ratherthanchemicalprocessesforphosphorusremovalfromwastewater.Sequentialanaerobic–aerobicoperationofacti-vatedsludgeprocessisappliedtoachieveenhancedbiolog-icalphosphorusremoval(EBPR).Thesimplestsystemcon-figurationforEBPRconsistsoftwostagesinseries,thefirstonebeinganaerobicandthesecondaerobic.Theactivatedsludge(biomass)iscycledbetweenanaerobicandaerobicphases,andtheinfluentissuppliedunderanaerobiccondi-tions.Operationinthismodelpromotestheaccumulationofphosphorusaccumulatingorganisms(PAO)[1].DuringtheEBPRanaerobicphase,carbonsubstratessuchasaceticandpropionicacidsaretakenupandsubsequently∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](Y.Chen).storedaspolyhydroxyalkanoates(PHA),whichincludepoly-3-hydroxybutyrate(PHB)andpoly-3-hydroxyvalerate(PHV).TheenergyandreductionequivalentrequiredforPHAbiosynthesisareprovidedbythedegradationofin-tracellularsavedpolyphosphate(poly-P)andglycogenaswellassubstratedegradationinthetricarboxylicacidcycle[2–4].Thebulkphosphorusconcentrationintheanaerobicperiodis,therefore,increasedwithtime.Inthesubsequentaerobicphase,wherenoexternalcarbonsourceispresent,theinternallystoredPHAareoxidisedandusedforcellgrowth,phosphateuptakeandpoly-Paccumulationandglycogensynthesis.InthesuccessfulEBPRprocess,theaerobicphosphateuptakeismuchhigherthantheanaerobicphosphaterelease,whichresultsinnetphosphateremoval.ThecarbonsubstratesobviouslyplayanimportantroleintheEBPRprocesssincetheyaretherawmaterialsofPHAbiosynthesis.Thebeneficialeffectofadditionofread-ilybiodegradablecarbonsources,suchasglucoseorfer-mentationproductsfromprimarysludgeanaerobicdigesters,0032-9592/$–seefrontmatter©2004ElsevierLtd.Allrightsreserved.doi:10.1016/j.procbio.2004.01.054724Y.Chenetal./ProcessBiochemistry40(2005)723–732suchasshort-chainfattyacidsortheirsalts(inthispapertheywereabbreviatedtoSCFA)hasbeenrecognisedintheliterature[5–7].However,untilnowmostofthestudiesoncarbonsubstrateaffectingEBPRarefocusedonacetateorglucose[1,3,8–12].TheinvestigationonotherSCFAsuchaspropionicacidinfluencingEBPRperformanceislimited[13–17].AspropionicacidisalsooneSCFA,additiontoaceticacidpresentinrealsewage[18],itisnecessarytoin-vestigatetheeffectofpropionicacidpresenceinwastewateronbothanaerobicandaerobicbehaviourofEBPR.ThestudiesofAbu-ghararahandRandall[13]inshort-termexperimentsshowedthephosphorusreleaseandup-takewithpropionicacidwaslessthanwithaceticacid,andthephosphorusuptaketoreleaseratiowithpropionicwasmuchlowerthanwithaceticacid.Satohetal.[14]alsoob-servedinanaerobicbatchexperimentsthatpropionicacidcausedlessphosphate-release/SCFA-uptakeratiothanaceticacid,andtheirmixtureresultedintheleastphosphatere-lease.ThestudiesofRandalletal.[15]indicatedthatpro-pionicacidexhibitedlowerphosphorusremovalthanaceticacidinthebatchexperiments.Withbiomassacclimatedbyacetate-containingsyntheticwastewater,RandallandLiu[17]usedbatchexperimentalresultstodiscussthereasonsforpropionicacidshowinglowerphosphorusremovalthanaceticacidfromthepointofPHBandPHV.TheyfoundthatpropionicacidaccumulatedlessPHBbutmorePHVthanaceticacid,whichwasthereasonforpropionicacidcausingmuchlessaerobicphosphateuptakethanaceticacid[17].However,theresultsofHoodandRandall[16]showedthatpropionicacidhadahigherphosphorusremovalthanaceticacidinthelong-termsequencebatchreactor