ARTICLEINPRESSWaterResearch38(2004)3719–3728www.elsevier.com/locate/watresNitrateremovalcharacteristicsofhighperformancefluidized-bedbiofilmreactorsFahidK.J.Rabah,MohamedF.DahabÃDepartmentofCivilEngineering,UniversityofNebraska-Lincoln,W348NebraskaHall,Lincoln,NE68588,USAAbstractTwolaboratory-scalehighperformancefluidizedbedbiofilmreactors(FBBR)withsandasthebiofilmcarrierwereusedtoinvestigatethedenitrificationofhigh-strengthnitratewastewaterwithspecificemphasisontheeffectthenitrogenloadingrateandthesuperficialvelocity(Vs).TheresultsdemonstratedthattheFBBRsystemiscapableofefficientlyhandlinganexceptionallyhighnitratenitrogenconcentrationof1000mgN/L.Ataloadingrateof6.3kg-N/3mbedÁdalmostcompletedenitrificationwasachievedwitharemovalefficiencyof99.8%andaneffluentconcentrationof2mgN/LatVsvaluesof45,55and65m/h.Themaximumefficientloadingrate(Rmax)atwhichtheUSdrinkingwaternitrate-nitrogenstandardconcentrationof10mgN/Lwouldbeexceededwasfoundtobeafunctionofthe3appliedVs.TheRmaxwasfoundtobe12kg-N/mbedÁdataVsvalueof45m/h.AsVswasincreasedto55and65m/h,3theoptimumRmaxdroppedto9.5and8kg-N/mbedÁd,respectively.HigherdenitrificationrateswereachievedatrelativelylowerVs.However,thereisaminimumpracticalvelocitybelowwhichagglomerationofbiomasswouldoccur.Thesuspendedsolidsconcentrationintheeffluentwasbelow30mg/Lthroughoutthestudy.r2004ElsevierLtd.Allrightsreserved.Keywords:Biofilm;Denitrification;Fluidized-bed;Nitrate;Nutrientremoval1.Introductionrequiredbystirredtankreactorsofsimilarcapacities(Gasseretal.,1975).ThisisattributedtothehighFluidizedbedbiofilmreactors(FBBR)fortreatingbiomassconcentrationthatcanbemaintainedinFBBRsindustrialandmunicipalwastewaterhavebeenusedforcomparedtothatintheactivatedsludgesystem;morethantwentyyears(Jerisetal.,1977;Suttonetal.,40,000mg/Lvs3000mg/L(Shiehetal.,1986).Biomass1981;Hareetal.,1988;SuttonandMishra,1994).TheconcentrationssimilartotheFBBRcanbeachievedinresultsfromlaboratoryandpilotscalestudieshavesomesuspendedgrowthtreatmentsyste