Performanceandoptimizationofbiologicalnitrogenremo

BiochemicalEngineeringJournal43(2009)280–287ContentslistsavailableatScienceDirectBiochemicalEngineeringJournaljournalhomepage:∗,LimingZhaib,d,YuWanga,ShuyingWangcaStateKeyLaboratoryofEnvironmentalAquaticChemistry,ResearchCenterforEco-EnvironmentalSciences,ChineseAcademyofSciences,Beijing,PRChinabSchoolofMunicipalandEnvironmentalEngineering,HarbinInstituteofTechnology,Harbin,PRChinacKeyLaboratoryofBeijingWaterQualityScienceandWaterEnvironmentRecoveryEngineering,BeijingUniversityofTechnology,Beijing,PRChinadDepartmentofCivilEngineering,HongKongUniversityofScienceandTechnology,ClearWaterBay,Kowloon,HongKongarticleinfoArticlehistory:Received21November2007Receivedinrevisedform6October2008Accepted18October2008Keywords:EnhancedbiologicalnitrogenremovalOptimizationBioreactorsBioprocessdesignStep-feedingprocessWastewatertreatmentabstractTheaimofthispaperistoinvestigatetheperformanceandoptimizationofanbiologicalnitrogenremovalprocessenhancedbytheanoxic/oxicfourstagesstep-feedingprocessundersufficient/insufficientinflu-entcarbonsource.Theconceptofinfluentflowdistributionratio()wasintroducedaccordingtotheperformanceofthestep-feedprocessforinflowsplittingandvolumedistribution.Undertheconditionofsufficientcarbon,theuniforminfluentflowdistributionratiowasproposedfromthestandpointofwhichiseasyforprocesscontrol,operationoptimizationandmanagement.UndertheconditionofdifferentinfluentC/Nratios,theoptimalinfluentflowdistributionratios(opt)weredetermined,bytrial-and-errormethod.Theresultsshowedthatmorethan95.81%ofthetotalnitrogenremovalefficiencycouldbeachievedbystep-feedingprocesswithafixedinfluentC/Nratio.AmodelwasintroducedtoderivetherelationshipsoftotalnitrogenremovalefficiencywithandinfluentC/Nratio.Whentheinfluentcar-bonsourcewasinsufficient,however,theoptbetweentwoadjacentstagesshouldnotbeuniform.Theresultsalsoshowedthatthefour-stagestep-feedingprocesswithoptof2.0:2.1:2.5:3.4couldsignificantlyimprovethetotalnitrogenremovalefficiency.TheresultsobtainedinthisstudywillhelptooptimizethedesignandtheoperationofBNRsystems.©2008ElsevierB.V.Allrightsreserved.1.IntroductionThebiologicaltechnologyfornitrogenandphosphorusremovalaimedforeutrophicationcontrolhasattractedamountofresearchinterests.Variousbiologicalnitrogenremovalprocesseshavebeendevelopedandwidelyused,suchaspre-denitrificationprocess(A/O),anaerobic/anoxic/aerobicprocess(A2O),UniversityofCapeTown(UCT)andmodifiedBardenphoprocesses.Theseapproachesrequireadditionalenergyforliquidcirculationandexternalcarbonsourceforanoxicdenitrification.Asaconsequencetheoperationalcostsignificantlyincreases.Comparedwithphosphorusremovalfromwastewater,nitrogencanonlyberemovedeffectivelyandeconomicallywithbiologicalmethods[1].Hence,itisnecessarytoexploreanddevelopnewbiologicalnitrogenremovalprocess[2–4].Anoxic/oxicstepfeedingactivatedsludgeprocesshasgainedmoreattentionowingtoitspromisingpotentialofnitrogen∗Correspondingauthorat:SchoolofMunicipalandEnvironmentalEngineering,HarbinInstituteofTechnology,Harbin,PRChina.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](Y.Peng).removal[5].Generally,itconsistsoftwoormoredenitrification–nitrificationunitsinseries,andtheenergyforinternalrecycleisunnecessary.Thesolidsretentiontime(SRT)canbeincreasedbecauseofconcentrationgradientofsuspendedsolid(SS)alongreactor.Basedonthesefeatures,thisprocesscouldoffersubstan-tialadvantagesfornewandexistingplants.Butmostofthestudieswerestillrestonthestageoftheoreticalanalysisandcomputersim-ulation[6–9].Someoperationalconcernsandpracticalexperienceswereaddressedfromextended,renewedorretrofittedconven-tionalactivatedsludgeprocess[10–13].Littleresearchisfocusedonthecharacterizationandoperationoptimizationofstep-feedbiologicalnitrogenremovalprocessintreatingdomesticsewage.Previousstudieshavebeenconductedtoevaluatetheeffectofinfluentflowratedistributiononthestep-feedbiologicalnitrogenremovalprocess.Theresultsdemonstratedthathightotalnitrogen(TN)removalefficiency,over95%,couldbeachievedundercer-taininfluentflowratedistributionwithoutinternalnitratecycleorexternalcarbonsourceaddition[14].Butadjustingflowratedistributionalonewithoutregulatingvolumeofeachstage,twonegativeimpactswouldoccur:firstly,nitrificationrateofeachstageunderdifferentinfluentflowdistributionsdecreasedalongwiththeincreasingofsludgeloadingandvolumeloadingineverystage;sec-ondly,ashighflowratedistributionratiowasneededforobtaining1369-703X/$–seefrontmatter©2008ElsevierB.V.Allrightsreserved.doi:10.1016/j.bej.2008.10.017G.Zhuetal./BiochemicalEngineeringJournal43(2009)280–287281Table1Compositionofsyntheticwastewaterinlaboratorypilot-scaleexperiment.CompoundConcentration(mg/L)Brewerywastewater9,500–10,500Glucose500–650Starch200–250NH4Cl114NaHCO3900MgSO4·7H2O150NaCl110CaCl285.5ZnSO490.0higherTNremovalefficiency,thesludgevolumeindex(SVI)valuewouldalsoincrease,resultinginoverloadandsludgebulking.Themainresearchpurposeofthisstudyistoinvesti