Single-sludge nitrogen removal: Modeling and experimental results

Laboratory-scale, single-sludge units were used to evaluate different kinetic, stoichiometric, and materials balance equations. Feed consisted of domestic wastewater spiked with carbonaceous organics and ammonium chloride. For approximately 2 mg/L of effluent ammonia or more, the nitrification reaction was zero-order. The specific nitrification rate was 2.3 g NH₄⁺-N/g N VSS· d. The minimum aerobic sludge age for nitrification at 20°C was 2.5 days. Denitrification was controlled by the COD removal reaction, which was best described by a first-order rate equation with a coefficient of 0.026 mg/L· d and 14 mg/L non-degradable COD. Nitrate utilization and endogenous respiration coefficients were 0.144 mg NO₃^- -N/mg COD · d and 0.007 g NO₃^- -N/g VSS · d. Effluent nitrate increased with increasing recycle because of low COD in the anoxic basin. The microbial composition of the biomass agreed qualitatively with predicted values.