The influence of nitrite and pH (nitrous acid) on aerobic-phase, autotrophic N2O generation in a wastewater treatment bioreactor.

Autotrophic ammonia oxidizing bacteria (AOB) are capable of generating nitrous oxide (N2O), via nitrite reduction, in oxygen-limited environments. The recognition of the environmental fate and effects of N2O, as a "greenhouse gas" has prompted researchers to study N2O generation and emission control in wastewater treatment systems. Oxygen, often expressed in terms of the bioreactor liquid dissolved oxygen concentration, is generally viewed as the most important variable with respect to influencing N2O generation. However, some literature data suggest that the nitrite concentration may also influence AOB N2O generation under oxygen-limited conditions, although there are contradictions in the reported information. This paper presents the findings of an investigation that specifically examined the sensitivity of aerobic-phase biomass N2O generation to changes in bioreactor nitrite concentration, via supply of exogenous nitrite, as well as changes in nitrous acid concentration through mixed liquor pH manipulation, in a bench-scale wastewater treatment bioreactor. The data demonstrate the significant influence of nitrite availability on biomass N2O generation in the studied system. Most of the collected data suggest that nitrous acid, as opposed to nitrite proper, was the actual AOB nitrite reductase (NiR) electron acceptor, based on observed N2O generation. In this case, the bioreactor mixed liquor pH, as well as nitrite concentration, would be important with respect to AOB N2O generation and greenhouse gas emissions. [ABSTRACT FROM AUTHOR]