Effect of Aeration Intensity on Nitrous Oxide Production

Abstract

Nitrous oxide (N 2 O) is known as one of the strong greenhouse gases and is emitted from aeration tanks of biological wastewater treatment plant. Strategy to control N 2 O emission from aeration tanks, however, has not been developed yet. We operated two identical pilot-scale anaerobic-anoxic-oxic (A2O) reactors to examine the effect of aeration intensity, especially to the first aerobic tank on N 2 O emission. The results indicate that the intensive aeration to the first aerobic tank increased N 2 O emission along with rapid ammonia oxidation and nitrite accumulation. On the contrary, moderate aeration provided gradual oxidation of ammonia, less nitrite accumulation and less N 2 O production. Batch tests with varied aeration intensities also demonstrated that intensive aeration enhances ammonium oxidation, resulting in the increased nitrite accumulation and the elevated N 2 O production, except in the case with high DO concentration (more than 2 mg/L). The conversion ratio of ammonia to N 2 O has good correlation to nitrite and nitrite/DO ratio. The effect of DO is complicated and still unclear. Mechanism of the elevated conversion to N 2 O is the effect of nitrite accumulation and might be the metabolic change of AOB.