Abstract
A performance comparison between the conventional anaerobic/anoxic/oxic (A 2 /O) process and the anoxic/anaerobic/oxic (reverse A 2 /O) process was conducted in lab‐scale at the hydraulic retention time of 0.75 d and solids retention time of 10 d for more than 200 days. Both processes demonstrated excellent removal efficiency for organic matter (> 96%) and total nitrogen (> 85%), with no significant difference in microbial activities, sludge phosphorus (P) content, sludge settling property, and nitrifying community (dominated by Nitrosomonas and Nitrospira ). However, there was significant difference in P removal, with the total P removal efficiencies in the reverse A 2 /O and A 2 /O systems of 76 ± 6% and 70 ± 6%, respectively. Placing an anoxic stage before the anaerobic stage in the reverse A 2 /O process resulted in a lower oxidation‐reduction potential (ORP = −268 ± 45 mV) of the anaerobic zone, which contributed to higher P uptake by bacteria under subsequent aerobic respiration.