This study was to investigate the removal efficiency and kinetics in oxidation of ammonia solutions (NH3-N) in ranging from 400 mg/L to 1000 mg/L by adding Cu/La/Ce catalyst in process of Wet Air Oxidation (denoted by WAO). All experiments were conducted in semi-batch and continuous reactors in series. The major parameters included temperature, pressure, concentration and pH.
In the semi-batch type of WAO experiments, the major parameters were performed at the following conditions: an initial concentration NH3-N of 400 mg/L, temperatures ranging from 423 K to 503 K, a total pressure of 4.0 Mpa, and a pH of 12.0. A removal efficiency of 32.7%was obtained in WAO process at 503 K for180 min, but it could be significantly promote to 95.1% after adding a catalyst of molar ratio 7:2:1.The kinetics of WAO with this catalyst in oxidation of NH3-N solutions, using a test of half-life, was developed nearly to a zero order. The reaction constants were 10.12 KJ/mol, 9.12 KJ/mol, and 6.57 KJ/mol at 503 K, 473 K and 423 K.
In the continuous type of WAO experiments, the major parameters were performed at the following conditions: an initial concentration NH3-N of 400 mg/L, a temperature of 503 K, a total pressure of 2.0 Mpa, a pH of 12.0 and a liquid space velocity of 4.5 hr-1 (averagelyresidence time 14 min) . A removal efficiency of NH3-N of 6.5 % only was achieved in WAO process for a space velocity of 4.5 hr-1 (averagely residence time 14 min) , but after adding a catalyst of molar ratio 7:2:1 it increased to 72.3 % for a same residence time and a better efficiency of above 91 % was found for 1.5 hr-1 (averagely residence time 40 min) . For increasing the initial concentration of NH3-N into 600 mg/L, 800 mg/L, and 1000 mg/L the removal efficiency of NH3-N decreased with 85 %,75 % and 69 % for 1.5 hr-1 . Thus, the initial concentration of NH3-N in influent inhibits the removal efficiency in the oxidation process. The higher initial concentration the lower removal efficiency.