Nitrous Oxide – a Powerful Greenhouse Gas with a Wastewater Treatment Connection

Although a ubiquitous element in nature, nitrogen has the potential for far-reaching environmental significance when considered in the context of the fate and impact of its various compounds in aquatic and atmospheric environments. Nitrous oxide (N2O) is a nitrogen compound largely unknown to the wastewater industry, but is a powerful greenhouse gas (GHG) due to its efficiency at trapping infra-red radiation. In recognition of this characteristic the Intergovernmental Panel on Climate Change (IPCC) has assigned N2O a global warming potential of approximately 310 units, relative to carbon dioxide. The connection of N2O to the wastewater industry lies in the biochemical pathways of autotrophic and heterotrophic bacteria, which can induce N2O generation in a variety of environments that include wastewater treatment bioreactors, effluent receiving water bodies and land receiving biosolids application. The objectives of this paper are to (i) provide an overview of the biochemical N2O generation pathways of interest in the context of wastewater management, (ii) present experimental data from a laboratory-scale study to illustrate the potential, and variability, of N2O generation in a wastewater treatment bioreactor, and (iii) using these data comment on bioreactor operation practices intended to encourage simultaneous nitrification and denitrification (SND) in the context of N2O emissions from wastewater treatment facilities.