Production and decomposition of nitrous oxide during biological denitrification

Nitrate (NO3) was reduced with methanol (MeOH) over denitrification‐filter sludge in a closed reactor. The initial reaction product was nitrous oxide (N2O). It accumulated to a maximum (N2Omax) and was then rapidly reduced to nitrogen (N2). At the time of maximum accumulation (tmax), 50 to 80% of the nitrate‐nitrogen reduced was in the form of N2O. These results led to a higher estimate of N2O emission from biological denitrification than previously considered. The results also suggest the concept of a multistage anoxic reactor in which nitrate can be reduced to N2 with minimal emission of N2O. The design would provide for retention of N2O in the upstream stages and reduction of N2O downstream.