The residual interference of do mainly includes:

1) based on the analysis of oxidation capacity data of molecular oxygen (O2) and nitrate (NO3-N) as electron acceptors, the capacity of O2 as electron acceptor is about 1.5 times of that of no3-n. therefore, when O2 and NO3-N exist in the system at the same time, denitrifying bacteria and common heterotrophic bacteria will preferentially metabolize the capacity of O2 as electron acceptor.

2) the presence of oxygen destroys the "anaerobic depression" environment needed by PAOs to release phosphorus, which results in anaerobic bacteria taking O2 as the final electron acceptor to inhibit its fermentation and acid production, hinders the normal release of phosphorus, and at the same time leads to the competition of carbon source between aerobic heterotrophic bacteria and PAOs.

Generally, do concentration in anaerobic zone should be strictly controlled below 0.2mg/l. In a sense, whether nitrate and do residues interfere with phosphorus release or denitrification is due to the competition of functional bacteria for carbon sources.