Nitrogen removal performance of CAST process with three operation modes

Fed with simulated domestic sewage, three reactors were operated under three operational modes (M1: conventional mode, M2: anoxic-aerobic mode, M3: alternant anoxic-aerobic mode) in order to evaluate the nitrogen removal performance of cyclic activated sludge technology (CAST) system. The removal efficiencies of total nitrogen in three operational modes were analyzed. In addition, in order to investigate the nitrogen removal pathway, nitrogen concentrations of a typical cycle under three operation modes were analyzed. Results showed that when NH₄⁺-N removal efficiencies were above 90%, the average removal efficiencies of total nitrogen under three operational modes were 67.3%, 70.6%, 82.4%, respectively. Furthermore, nitrification via nitrite was achieved under all operation modes. However, along with the rising of temperature, nitrification via nitrite disappeared. The static tests demonstrated that the ammonia oxidation rates under three operation modes were: v_N:M1>v_N:M2>v_N:M3 and denitrification rates were: v_DN,M2>v_DN,M3>v_DN,M1.