The confounding effect of nitrite on N2O production by an enriched ammonia-oxidizing culture

Abstract

The effect of nitrite (NO2–) on the nitrous oxide (N2O) production rate of an enriched ammonia-oxidizing bacteria (AOB) culture was characterized over a concentration range of 0–1000 mg N/L. The AOB culture was enriched in a nitritation system fed with synthetic anaerobic digester liquor. The N2O production rate was highest at NO2– concentrations of less than 50 mg N/L. At dissolved oxygen (DO) concentration of 0.55 mg O2/L, further increases in NO2– concentration from 50 to 500 mg N/L resulted in a gradual decrease in N2O production rate, which maintained at its lowest level of 0.20 mg N2O–N/h/g VSS in the NO2– concentration range of 500–1000 mg N/L. The observed NO2–-induced decrease in N2O production was even more apparent at increased DO concentration. At DO concentrations of 1.30 and 2.30 mg O2/L, the lowest N2O production rate (0.25 mg N2O–N/h/g VSS) was attained at a lower NO2– concentration of 200–250 mg N/L. These observations suggest that N2O production by the culture is diminished by both high NO2– and high DO concentrations. Collectively, the findings show that exceedingly high NO2– concentrations in nitritation systems could lead to decreased N2O production. Further studies are required to determine the extent to which the same response to NO2– is observed across different AOB cultures.