Study on nitrogen removal of simultaneous nitrification and denitrification in BAF

In order to meet the requirements of replenishment water in the section of the North Canal in Tong-zhou, Beijing, the experiment was carried out usingpre-denitrification BAF andpolyurethane filler. The factors of simultaneous nitrification and denitrification have been studied: gas-water ratio, reflux ratio, hydraulic loading and filter height. When the aerobic section of the gas-water ratio was 20:1, the reactor possessed obvious feature of simultaneous nitrification and denitrification, with the total nitrogen removal ratio, of 82.96%, and its´ concentration in the effluent less than the 10mg/L; When the reflux ratio was 1:1, anoxic tank removal rate was 42.3%, while aerobic tank removal rate was 51.85%; When the hydraulic loading was 0.32m³/(m² ·h), the concentration and removal rate of TN in the effluent were 11mg/L and 76.67%, respectively, at which time simultaneous nitrogen removal rate of aerobic tank reached peak. Sampling along the layer in the aerobic area, the results showed that the total nitrogen removal mainly occurred at the bottom of the reactor ranging between 0 and 0.6m; when DO is between 1.5 and 2mg/L, the SND is obvious, and the TN removal rate remained above 80%. By simultaneously monitoring changes of ORP values along the layer, the ORP during the simultaneous nitrification and denitrification process can send control signal and respond stably and sensitively. According to the changes of ORP, the aeration area can be adjusted efficiently to save energy.