Inhibitory effect kinetics of nitrite acting as electron acceptor on anoxic phosphorus uptake and denitrification

Nitrite has been found in previous research an inhibitor on anoxic phosphorus uptake in enhanced biological phosphorus removal systems (EBPR). However, the inhibiting nitrite concentration reported varied in a large range and no kinetics study concerned on anoxic phosphorus uptake. This study investigates the nitrite inhibition on anoxic phosphorus uptake with sequencing batch reactor (SBR) in different concentrations of NO2- and under different pH gradient. The activated sludge was cultured with A/O Oxidation Ditch pilot-scale reactor performing EBPR. The progress of SBR is as follows: the activated sludge was taken out an aerobic zone of the A2/O Oxidation Ditch to SBR, then phosphorus was released with acetate fed in anaerobic phase, subsequently phosphorus uptake proceeded with NO2- added in anoxic phase. It is pointed that not only NO2- but pH inhibited anoxic phosphorus uptake. The result indicated that (1) specific denitrification rate and specific phosphorus uptake rate correlated the original nitrite accord with Andrews' s inhibition model under the constant pH. (2) If pH was in the range of 6.5 to 8.0, nitrite inhibited DPR much stronger when pH was less, vice versa. (3) Kinetics parameter was as follows: the max specific denitrification rate was 4.55 mg/(g·h), the half saturation constant of the denitrification process was 2.14 mg/L; and the max specific phosphorus uptake rate was 3.06 mg/(g·h), the half saturation constant of the phosphorus uptake process was 2.64 mg/L.