The Impact of Post Anoxic Dissolved Oxygen Concentrations on nitrous Oxide Emissions in Nitrification Processes

Emissions of nitrous oxide (N2O) from wastewater treatment plants have become a prominent field of study in terms of emissions inventories and mechanisms behind their production. This study aims to analytically determine the impact of select recovery dissolved oxygen (DO) concentrations on N2O emissions from a nitrifying enrichment culture, subjected to a 6 hour anoxic period followed by a recovery aeration period. This study examined three different recovery DO set points, a low value of 0.8mg/L, an intermediate value of 2mg/L, and a high value of 3mg/L. As such, three different N2O emissions profiles were produced illustrating the distinct response of the microbial cultures to the imposition of a transient anoxic period and subsequent ammonia accumulation vis-à-vis N2O emissions. Higher emissions were observed at the higher recovery DO values of 2.0 and 3.0 mg O2/L. Based on proposed metabolic pathways for autotrophic ammonia oxidation, N2O emissions in response to anoxic-oxic transients appear to be linked to interim hydroxylamine accumulation and subsequent oxidation either to nitrite or nitric oxide.