Study on Biological Nnitrogen Removal in a Combined A/O Biofilm Reactor

A combined A/O biofilm reactor was designed to treat domestic wastewater. The effect of hydraulic retention time (HRT), dissolved oxygen (DO) and nitrifying fluid return ratio on the nitrogen removal was investigated. The experimental results were as following: HRT had a greater effect on COD removal. When without nitrifying fluid return, the most of NH₄ ⁺-N was removed in B zone; When HRT was less than 6.5 h or DO in O and B was lower than 3~4 and 6~7 mg/L, respectively, the concentration of NH₄ ⁺-N in the effluent increased. After the nitrifying fluid return was carried out, the efficiency of NH₄ ⁺-N removal increased greatly, and at the same time, the efficiency of TN removal increased greatly than that without nitrifying fluid return. With HRT of 6.5 h, return ratio of 150%, DO of 3~4 mg/L and 6~7 mg/L in O and B zone, respectively, the average COD loading of 1.10 kg/m³.d and NH₄ ⁺-N loading of 0.15 kg/m³.d, the efficiency of NH₄ ⁺-N and TN removal in the reactor reached 99.00% and 76.60%, respectively, and the average NH₄ ⁺-N and TN in the effluent were 0.40 mg/L and 10.82 mg/L, which met the A-level standard in GB 18918-2002.