[Effects of Side-stream Phosphorus Recovery on the Performance of EBPR System Under Low Dissolved Oxygen Condition]

A sequencing batch reactor (SBR) was operated with alternating anaerobic/oxic (An/O) condition to investigate the nitrogen and phosphorus removal performance of EBPR with DO=1 mg·L^-1 and the phosphorus recovery effect at extracting side stream ratio of 0, 1/4, 1/3, 1/2 anaerobic phosphorus supernatant. The removal efficiency of NH₄⁺-N was found to be relatively stable during all experimental stages but effluent COD of the system during later period remained as high as 81.3 mg·L^-1. In the absence of side stream, the average phosphorus removal efficiency was 89.4% and increased to 98.5% and 99.0% when the side stream ratio was 1/4 and 1/3, respectively. However, the phosphorus removal performance began to fluctuate with side stream ratio of 1/2 and the lowest phosphorus removal rate was 65.4%. During each experimental stage, only one day effluent TP failed to meet the national wastewater discharge standard A with side stream ratio of 1/3 in the initial period. Besides, 93.3% of effluent TP which could meet the national standard with side stream ratio of 1/3 was far better than 45.5% of that with side stream ratio of 1/2. Nevertheless, the phosphorus recovery rate improved with the increase of side stream ratio. It was also observed that the TN removal rate dramatically decreased to 50.9% when the side stream ratio increased to 1/2. Consequently, a side stream ratio of 1/3 was found to be the optimal condition in the whole experimental stage, and EBPR system under low dissolved oxygen condition combined with phosphorus recovery through extracting side stream could greatly improve the economic and environmental benefits.