Enhanced Biological Nutrients Removal in Modified Step-feed Anaerobic/Anoxic/Oxic Process

In order to enhance phosphorus removal in traditional step-feed anoxic/oxic nitrogen removal process, a modified pilot-scale step-feed anaerobic/anoxic/oxic (SFA2/O) system was developed, which combined a reactor similar to UCT-type configuration and two-stage anoxic/oxic process. The simultaneous nitrogen and phosphorus removal capacities and the potential of denitrifying phosphorus removal, in particular, were investigated with four different feeding patterns using real municipal wastewater. The results showed that the feeding ratios (Q1) in the first stage determined the nutrient removal performance in the SFA2/O system. The average phosphorus removal efficiency increased from 19.17% to 96.25% as Q1 was gradually increased from run 1 to run 4, but the nitrogen removal efficiency exhibited a different tendency, which attained a maximum 73.61% in run 3 and then decreased to 59.62% in run 4. As a compromise between nitrogen and phosphorus removal, run 3 (Q10.45Qtotal) was identified as the optimal and stable case with the maximum anoxic phosphorus uptake rate of 1.58 mg·(g MLSS)−1·h−1. The results of batch tests showed that ratio of the anoxic phosphate uptake capacity to the aerobic phosphate uptake capacity increased from 11.96% to 36.85% with the optimal influent feeding ratio to the system in run 3, which demonstrated that the denitrifying polyP accumulating organisms could be accumulated and contributed more to the total phosphorus removal by optimizing the inflow ratio distribution. However, the nitrate recirculation to anoxic zone and influent feeding ratios should be carefully controlled for carbon source saving.