Pilot and Full-Scale Evaluation of Biological Nutrient Removal Using Anoxic-Anaerobic-Aerobic Process

A new BNR process, the Anoxic-Anaerobic-Aerobic process (also referred to as the Reversed A2O process) was evaluated for phosphorus (P) and nitrogen (N) removal at laboratory, pilot, and full scales. Unlike conventional biological nutrient removal processes, the activated sludge in an Anoxic-Anaerobic-Aerobic process is subjected to a sequence of anoxic-anaerobic-aerobic conditions. Nitrate is recycled to the beginning of the anoxic zone along with return activated sludge, eliminating the need for an internal recycle. The results of laboratory, pilot and full-scale studies showed that Anoxic-Anaerobic-Aerobic process is an efficient biological nutrient removal process. The results of this study also suggest that the degree of effective P-release is not the sufficient and necessary condition determining the ability of excess P-uptake in the following aerobic environment. The driving force for excessive phosphorus uptake of phosphorus accumulating organisms is related to the anaerobic retention time and degree. When other factors are fixed, a longer anaerobic retention time and more sufficient anaerobic degree will result in a greater P-uptake potential in the aerobic zone.