The objective of this study was to investigate dynamic specific denitrification rates (SDNRs) from nitrite at various chemical oxygen demand (COD)/nitrogen (N) ratios using municipal wastewater (MWW). A sequencing batch reactor (SBR) continuously fed with primary effluent and nitrite solution was operated at hydraulic retention time of 8.4 hr and solids retention time of 26-30 days for 3 months. Influent MWW characteristics varied significantly during the study, that is, 200-810 mgCOD/L and 6-80 mgN/L. The SDNRs from the SBR were compared with those determined in four batch reactors using acetate. The SDNR was directly related to COD/N until a maximum SDNR (mgNO2 -N/mgVSS/day) of 0.07 for MWW and 0.4 for acetate occurred at COD/N ratios of 6 and 13, respectively; beyond this COD/N ratio, SDNR decreased. The biomass yield coefficients (mgVSS/mgCOD) were 0.33 for MWW and 0.51 for acetate. The relationships of SDNR with COD/N and F/M ratios were developed. PRACTITIONER POINTS: The optimum carbon dose for denitrification should be determined using acclimatized biomass. Each carbon source should only be dosed at an optimum that maximizes denitrification.
Keywords: COD/N ratio; external carbon source; municipal wastewater; nitrite; predenitrification; specific denitrification rate.
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