No abstract

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.

A pilot-scale nitrogen removal system composed of an anoxic area, an anaerobic area, a microaerobic area and an aerobic area (A2O2) was established to treat high strength ammonium wastewater from a nitrogenous fertilizer factory. The influences of key factors such as DO, pH, FA and temperature on partial nitrification in the microaerobic area were investigated. The results showed that in the DO concentration of 0.5~0.7mg/L, the stable and efficient nitrite accumulation could be realized. Meanwhile, the effluent NH3-N and TN quality was superior to the requirement of the《Synthetic ammonia industrial water contamination emission standard》(draft for comment). The optimal pH of 7.5~8.0 and the corresponding free ammonia (FA) concentration of around 0.95 mg/L limited the nitrobacteria activity selectively, thus favoring the stability of partial nitrification. The nitrite accumulation rate didn’t show obvious difference in wide temperature range (18~35°C) at given DO (0.5~0.7mg/L) and pH (7.5~8.0). But contrary to the usual partial nitrification obtained by high temperatures (>30°C), the effluent ammonium of A2O2system was substandard due to the inhibition of nitrobacteria activity caused by high temperature, which diminished the further removal of ammonium in the subsequent aerobic area.

The pilot-scale Anoxic-Anaerobic-Microaerobic-Aerobic (A2O2) biological nitrogen removal process was used to treat the wastewater from nitrogenous fertilizer production with C/N ratio of 1~2. Batch tests were conducted to investigate the patial nitrification using the activated sludge from the microaerobic tank rich in nitrite bacteria as the experimental object. Results showed that 95% removal efficiency of NH3-N could be obtained with the HRT of 30 h. The SVI affected the NH3-N removal rate and the optimal SVI was 106 mL/g. The ORP was well correlated with the logarithm of NH3-N concentration with the linear regression equation of y=-57.233x+3.308. Moreover, the kinetic model for partial nitrification was determined as v=4.762s/(9.86+s).