Nitrification kinetics of a full-scale anaerobic/anoxic/aerobic wastewater treatment plant

Nitrification kinetics of a full-scale anaerobic/anoxic/aerobic wastewater treatment plant were investigated by considering the anaerobic (η_A) and anoxic reduction factors (η_N) on decay rate of nitrifying biomass (b_AUT) for estimating minimum sludge age (θ_mc). Ammonium nitrogen in the effluent was fluctuating seasonally with low nitrification efficiency from December to June. The measured b_AUT values were 0.175, 0.092, and 0.077 d⁻¹ under aerobic, anoxic, and anaerobic conditions, respectively. A low maximum specific growth rate at 20°C (0.48 d⁻¹) and high temperature correction factor (1.208) were yielded in the range of 10–25°C, indicating that the activity of nitrifying biomass was low and depended more sensitively on lower temperatures. At temperature below 12.1°C, the decay rate of nitrifying biomass exceeded growth rate, and a negative θ_mc was obtained. The extremely high (12.1–15.0°C) or negative (<12.1°C) θ_mc indicated that prolonging sludge age was probably malfunctioned at cold temperature.