Abstract
It is well known that N2O, a greenhouse gas, is produced during biological nitrogen removal in wastewater treatment plants (WWTPs). It has been reported that the amount of N2O emitted varies depending on the type of WWTP and even within the same WWTP depending on the operational conditions. Therefore, it is important to consider the conditions that can reduce the amount of N2O emission and to investigate the pathway of N2O production by studying the N2O production potential and the amount of N2O emission.In our sealed batch experiments where NO2-N was added as the precursor substance for N2O production, the amount of N2O produced under aerobic conditions increased with higher initial NO2-N concentrations and longer reaction times. Consequently, the initial NO2-N concentration of 5 mgN•L-1 and a reaction time of 1 h were selected to evaluate the N2O production activity. The high N2O production activity in an actual WWTP was observed when nitrification was controlled; however, N2O production activity decreased when nitrification was accelerated. This was likely to be due to the competing processes of NO2-N reduction to N2O with NO2-N oxidation to NO3-N. Furthermore, the operational conditions under which Nitrospira caused complete nitrification inhibited N2O emission.
