PRODUCTION OF NITROUS-OXIDE GAS DURING NITRIFICATION OF WASTE-WATER

Laboratory-scale experiments were conducted to examine nitrous oxide ( N2O) production during the nitrification process. Substrate containing 400 mgN l(-1) of NH4HCO3 as a nitrogen source was continuously fed in to a 10 or 3 liter completely mixed reactor with varied dissolved oxyg en (DO) and SRT. The DO of the continuous systems were fixed at 0.1, 0 .2, 0.5, 1.7 and 6.8 mg l(-1). The SRT were controlled at 3, 5, 10 and 20 days. Total amount of N2O production reached higher than 36 mgN l( -1) in some conditions, and up to 16% of nitrified nitrogen was conver ted into N2O. N2O production was observed in all tested runs. Lower DO and shorter SRT resulted in higher N2O production. Incomplete nitrifi cation was found at DO lower than 0.5 mg l(-1) and an SRT shorter than 5 days. The highest concentration and conversion rate of N2O producti on was obtained at DO of 0.2 mg l(-1) or when SRT was 3 days. The resu lts suggest that N2O production is significant during nitrification pr ocess. The accumulation of NO2 may contribute to the high amount of N2 O production.