[Effect of free ammonia on the short-cut nitrification of the municipal landfill leachate].

A system consisting of a two-stage UASB and anoxic-oxic reactor was used to study the influence of FA on short-cut nitrification of the actual municipal landfill leachate with high ammonia concentration. In the UASB1, denitrification and methanogenesis took place simultaneously. The effluent COD of UASB1 was further removed in the UASB2. Then the denitrification of nitrite and nitrate in the returned sludge by using the residual COD and nitrification was finished in the A/O reactor. The experiment experienced three stages during 79 d. The stable short-cut nitrification was achieved in the first stage (40 d). The short-cut nitrification was damaged in the second stage (19 d), and the short-cut nitrification was recovered in the last stage (20 d). The results of 79 d showed that when the FA concentration was about 40-70 mg x L(-1), the stable short-cut nitrification could be achieved. For example, the nitrite accumulation was 97% in the system during the first stage, and the ammonia removal efficiency was 99%. But when the FA concentration was about 160 mg x L(-1), the nitrification would be inhibited. In the third stage, raw leachate was diluted by tap water in order to decrease the FA concentration. And then the short-cut nitrification was recovered soon. In a word, the FA concentration is an important factor to achieve the short-cut nitrification of the municipal landfill leachate.