Performance of phosphorus and nitrogen removal for the low COD/N ratio in urban wastewater by modified A~2/O process

摘要

A modified A~2/O process was proposed to solve the problems (carbon source competing, sludge age contradicting, and so on) produced during nitrogen and phosphorus removal process by adding fillers according to the current widely applied A~2/O process in the urban wastewater treatment plants aiming to treat the low COD/TN ratio wastewater coming from Mudanjiang city. By controlling the flowing speed of backwashing sludge to the preanoxic zone, the optimum phosphorus releasing results were obtained and its influence to phosphorus releasing was also discussed. The relation had also been demonstrated between the backflowing sludge to oxic zone and ammonium removal rate. Meanwhile, the influence of nitrified liquid recirculation to anoxic zone to the total ammonium removal process had also been explained. The optimum operating condition had been determined. The influence also had been demonstrated with the adjustment of the sludge age to the nitrogen and phosphorus removal in the modified A~2/O process. Results showed that the modified A~2/O process can solve the problem of organic matter competing between denitrifying and phosphorus-accumulating bacteria. The contradiction of sludge age in the ammonium and phosphorus removal process can be mitigated by adding the fillers.