Competition for Single Carbon Source Between Denitrification and Phosphorus Release in Sludge under Anoxic Condition

In order to investigate the competition for carbon source between denitrification and phosphorus release processes, simultaneous phosphorus release and denitrification in sludge operated in anoxic, aerobic mode are investigated by varying the ratio of influent COD to nitrogenous compound concentration under anoxic condition using a lab-scale sequencing batch reactor (SBR). The results show that the nitrate reduction rate is nearly independent of the ratio of influent COD to nitrate under anoxic condition. More NO−x -N in the influent leads to less PO3−4 -P release during the feeding period. However, PO3−4 -P release proceeds at a low rate simultaneously with denitrification even when the influent NO−x -N concentration is as large as 20 mg·L−1 and its rate is increased obviously when NO−x -N is denitrified to a concentration lower than 0.5 mg·L−1. The variation of pH during anoxic period gives some information about the biochemical reactions of denitrification and PO3−4 -P release. When more nitrate is present in the influent, more acetate uptake in feeding period is used for direct microorganism growth.