Denitrifying Phosphorus Removal in a Continuously-Flow A2N Two-Sludge Process

Abstract

The Anaerobic-Anoxic/Nitrification (A2N) system is a continuous-flow, two-sludge process in which Poly-p bacteria are capable of taking up phosphate under anoxic conditions using nitrate as an electron acceptor. The process is very efficient because it maximizes the utilization of organic substrate for phosphorus and nitrogen removal. Further, the process solves the competition for organic substrate among Poly-p organisms and denitrifies as well as the problem of overgrowing of slow nitrifiers by fast organotrophs. An experimental lab-scale A2N system fed with domestic sewage was tested over a period of 260 days. The purpose of the experiment was to examine phosphorus removal capacity of a modified A2N two-sludge system. Factors affecting phosphorus and nitrogen removal by the A2N system were investigated. These factors were the influent COD/TN ratio, Sludge Retention Time (SRT), Bypass Sludgy Flow rate (BSF), and Return Sludge Flow rate (RSF). Results indicated that optimum conditions for phosphorus and nitrogen removal were the influent COD/TN ratio around 6.49, the SRT of 14 days, and the BSF and RSF were fixed about 26%–33% of influent flow rate.