Nitrogen Removal in Full-Scale "Anoxic Anaerobic Micro-Aerobic Aerobic (A₂O₂)" System Treating Wastewater of Nitrogenous Fertilizer Factory

A full-scale nitrogen removal system composed of an anoxic tank, an anaerobic tank, a micro-aerobic tank and an aerobic tank (A2O₂) was established to treat 15,000 t/d high strength ammonia wastewater of a nitrogenous fertilizer factory. After the first stage of commissioning test, the stable operation of short-cut nitrification and denitrification has been realized at the normal temperature. The results showed that under the conditions of COD/TN ratio of only 1~2, the average removal efficiency of COD、NH3-N and TN achieved 80%, 96% and 54%, respectively without extra addition of alkalinity or carbon source, and the effluent quality was better than the requirement of the《Synthetic ammonia industrial water contamination emission standard》(draft for comment). The variation of nitrogen compounds concentration and operational parameters of pH, DO were investigated in each tank of A2O₂ system. The results showed that the short-cut nitrification was stabilized in the micro-aerobic tank through the control of DO concentration (about 0.6 mg/L). Although the pH of micro-aerobic tank was only 6.6 which inhibited the growth of nitrite bacteria, the nitrite accumulation ratio reached about 48 %, closing to the criteria for judgment of short-cut nitrification of 50%. During operation, the process parameters of the A2O₂ system such as reflux ratio of the mixed liquids, sludge load, sludge concentration, sludge age and SVI were all maintained in normal range, and small fluctuation of process parameters didn’t show obvious influence on short-cut nitrification.