Anoxic-growth-of-phosphate-accumulating-organisms-(PAOs)

WaterResearch36(2002)4927–4937Anoxicgrowthofphosphate-accumulatingorganisms(PAOs)inbiologicalnutrientremovalactivatedsludgesystemsZhi-rongHu*,M.C.Wentzel,G.A.EkamaDepartmentofCivilEngineering,WaterResearchGroup,UniversityofCapeTown,Rondebosch7701,Cape,SouthAfricaAbstractInthispaper,researchonthegrowthperformanceofphosphate-accumulatingorganisms(PAOs)wasconductedbasedonliteratureandexperimentalinvestigationsonbiologicalnutrientremoval(BNR)activatedsludge(BNRAS)systems.TheresearchaimsatpresentingtheoccurrenceofdenitrifyingPAOs(DPAOs),abstractinginformationonthekineticsandstoichiometryofPAOsunderanoxicconditionsanddeterminingtheconditionsthatstimulatethePAOgrowthunderanoxicconditions.TheresearchresultsindicatethatthePAOsarecapableofutilizingnitrateaselectronacceptorinsteadofoxygeninBNRASsystems,particularlyinexternalnitrificationBNRAS(ENBNRAS)systems.However,thegrowthyieldofPAOsunderanoxicconditionsshouldbereducedtoabout70%ofthatunderaerobicconditions,andfurtherthestoichiometriccoefficientforanoxicPuptakeperPHBCODutilizedshouldbereducedtoabout80%ofthatunderaerobicconditionsastheDPAOsshowasignificantlylowerBEPRperformanceandusetheinfluentRBCODless‘‘efficiently’’comparedwithaerobicPAOs(APAOs).TheresearchresultsalsoindicatethatthemajorfactorinfluencingtheoccurrenceofDPAOsandassociatedanoxicPuptakeisthenitrateloadintotheanoxicreactor,i.e.thenitrateloadshouldbelargeenoughorexceedsthedenitrificationpotentialofordinaryheterotrophicorganisms(OHOs),i.e.non-PAOorganismsintheanoxicreactortostimulateDPAOsinthesystemasthespecificdenitrificationrateofOHOs(K02OHO)issignificantlylargerthanthatofPAOs(K02PAO).Intermsofthiscompetition,ifthenitrateloadintothemainanoxicreactorislessthanthedenitrificationpotentialofOHOs,thentheOHOswilloutcompetePAOsforusingthelimitednitrate,whileifthenitrateloadinthemainanoxicreactorexceedsthedenitrificationpotentialofOHOs,thenthePAOswouldhaveopportunitiestousethe‘‘excess’’nitrateandsodevelopinthesystem.TheotherfactorsthatinfluenceDPAOsincludethesystemaerob