The simultaneous nitrification and denitrification characteristics of two-stage biological aerated filter

The two-stage biological aerated filter (BAF) was adopted to carry out the experimental study of actual domestic wastewater, the hydraulic loading of 22.01 m³/(m²·d) and the air/water ratio of 6:1 at A-stage were controlled, when air/water ratio was 3:1, 2:1 and 1:1 respectively at B-stage, the operation state of reactor was studied. The effluent quality was stable and excellent, and the removal effect of every pollutant was the best when the air/water ratio was 2:1 at B-stage reactor. B-stage possessed marked of simultaneous nitrification and denitrification characteristics. Short-cut simultaneous nitrification and denitrification was carried out mainly when air/water ratio was lower. Static experiment was carried out for biofilm at 0.9-meter height of B-stage reactor. The specific nitrification rate of the biofilm was 1.458 mg NH₃-N/(gMLSS·h); the existence of organic carbon source did not affect the operation of nitrification under the adaptable state of affecting factors, such as DO and pH, et al. In denitrification process the denitrification rate over nitrite was 1.15 times higher of that over nitrate, thus, the denitrification time was also shortened.