Evaluation of Anaerobic/Anoxic/Oxic (A²/O) and Reverse A²/O Processes in Biological Nutrient Removal

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 6% and 70 6 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 ¼À 268 6 45 mV) of the anaerobic zone, which contributed to higher P uptake by bacteria under subsequent aerobic respiration. Water Environ. Res., 86, 2186Res., 86, (2014.

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