Effects of Free Ammonia on Partial Nitrification under Different Conditions

Partial nitrification to nitrite is technically feasible and economically favourable, especially when wastewaters contain high ammonium concentrations. Partial nitrification can be obtained in situations of free ammonia inhibition the nitrite oxidizer but not the ammonia oxidizer. The effects of free ammonia on partial nitrification for treating old landfill leachate were investigated with different DO concentrations, pH values and temperature and in order to achieving partial nitrification with high nitrite accumulation rate and ammonia oxidation rate. Results show that when the ammonia oxidizer and the nitrite oxidizer are restricted by low DO, the lower Free ammonia (FA) concentration could inhibit the activity of them, and the high nitrite accumulation rate can be achieved under the nitrite oxidizer being inhibited solely by FA. Concentration of free ammonia inhibition at temperature below 22°C was lower than that above 22°C . When temperature is between 22°C and 35°C, higher nitrite accumulation rate and ammonia oxidation through FA inhibiting nitrite oxidizer could be achieved. The pH values suitable to the ammonia oxidizer and nitrite oxidizer were 7.0~8.5 and 7.0~8.0, respectively. The appropriate pH values for the nitrosomonas was higher than that for nitrobacteria, for which the high ammonia oxidation rate and nitrate accumulate rate could been achieved through the FA inhibition nitrobacteria in the pH 8.0-8.5.