Simultaneous removal of nitrogen and phosphorus with A2/O process using immobilized media.

It is necessary to introduce nitrogen and phosphorus removal processes in the existing wastewater treatment plants of Fukuoka City to improve the water quality of Hakata Bay. An A2/O (anaerobic-anoxic-oxic) process using immobilized media is proposed here, as a high-end technology to meet stricter discharge standards when faced with treatment space limitations. In order to investigate the applicability of the process, a pilot-scale study using municipal wastewater was conducted. Fluidized immobilization media were added to the aerobic reactor to maintain a high concentration of nitrifying bacteria and nitrification rate. Relationships between nutrient removal performance and varied operating conditions were examined. The results of the pilot plant test indicated that the process performs well for removal of nitrogen and phosphorus. Under the condition of HRT = 8 hr, it was possible to obtain an effluent water quality as follows: T-N<8.0 mg/L; T-P<1.0 mg/L. It was observed that reaction time needed for a complete nitrification was shortened by the addition of immobilized media to the aerobic reactor, and longer reaction time would be needed for a completed phosphorus uptake process other than complete nitrification in an aerobic tank. Therefore, the phosphorus uptake rate, as well as nitrification process, should be considered as one of the important factors affecting the design parameters of an aerobic reactor.