N₂O emission during nitrification in constant flow biological wastewater treatment systems

Nitrification in biological nitrogen removal from wastewater is a main source of nitrous oxide (N₂O). Two constant flow reactors were operated to enrich nitrifiers with two influent ammonium (NH₄-N) concentrations of 60 mg/L (low-N-reactor) and 180 mg/L (high-N-reactor), and then effects of different initial NH₄-N concentrations and initial nitrite (NO₂-N) concentrations on the N₂O emission for the acclimated nitrifiers were examined. There was not much N₂O emission during the constant operation of the reactors, with the ratio of N₂O emission to the removed NH₄-N less than 0.01%. N₂O emission increased with increasing both initial NH₄-N and NO₂-N concentrations. At different initial NH₄-N concentrations, the ratio of N₂O emission to the removed NH₄-N was in the range from 0.51% to 1.40% for activated sludge from the low-N-reactor and from 0.29% to 1.27% from the high-N-reactor. At different initial NO₂-N concentrations, the ratio of N₂O emission to the removed NH₄-N was in the range from 1.38% to 3.78% for activated sludge from the low-N-reactor and from 1.16% to 5.81% from the high-N-reactor.