An experimental procedure for identifying the aerobic-phase biological source of nitrous oxide in anoxic–aerobic wastewater treatment systems

Abstract

This paper describes a relatively simple experimental procedure used to assess the relative contribution of autotrophic and heterotrophic organisms in the generation of aerobic-phase nitrous oxide from a mixed microbial population in a bench-scale, anoxic–aerobic, sequencing batch reactor (SBR) wastewater treatment system. The procedure eliminated ammonia oxidation from a "perturbation" cycle, while maintaining pH and dissolved oxygen levels similar to the "baseline" cycle. Nitrite and carbon oxidation were maintained during the perturbation cycle. Compared to more complex methods such as stable isotope labelling techniques, the described procedure is logistically simple and requires equipment readily available in most environmental engineering laboratories. When applied to an SBR system treating synthetic wastewater (influent ammonia N concentration = 160 mg/L), the experimental results strongly suggest that essentially all of the nitrous oxide produced during the aerobic phase of the cycle was generated by autotrophic, ammonia oxidizing organisms. Little, if any, nitrous oxide appeared to be generated by heterotrophic denitrification during the aerobic phase of the cycle. Key words: nitrification, aerobic denitrification, nitrous oxide, nitrite reduction.