A modeling understanding on the phosphorous removal performances of AO and reversed AO processes in a full-scale wastewater treatment plant.

Reversed AO process (anoxic-anaerobic-aerobic) and conventional AO process (anaerobic-anoxic-aerobic) are widely used in many wastewater treatment plants (WWTPs) in Asia. However, at present, there are still no consistent results to figure out which process has better total phosphorous (TP) removal performance and the mechanism for this difference was not clear yet. In this study, the treatment performances of both processes were compared in the same full-scale WWTP and the TP removal dynamics was analyzed by a modeling method. The treatment performance of full-scale WWTP showed the TP removal efficiency of the reversed AO process was more efficient than in the conventional AO process. The modeling results further reveal that the TP removal depends highly on the concentration and composition of influent COD. It had more efficient TP removal than the conventional AO process only under conditions of sufficient influent COD and high fermentation products content. This study may lay a foundation for appropriate selection and optimization of treatment processes to suit practical wastewater properties.