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.