GHG EMISSIONS, NITROUS OXIDE AND YOUR BIOREACTOR – THINGS TO THINK ABOUT

Greenhouse gas (GHG) emissions and the carbon footprint of wastewater treatment facilities have quickly become important topics of interest to municipalities and utilities. Nitrous oxide (N2O) is a powerful GHG with a global warming potential approximately 300 x carbon dioxide and it can be generated by microorganisms within a bioreactor. Oxygen is a key substrate that influences the N2O generation potential. Provision of excess oxygen to the bioreactor can practically eliminate N2O generation, but such an approach comes at a cost in terms of power needed to supply oxygen and carbon dioxide equivalents associated with off-site electrical power generation. This paper examines the sensitivity of a strategy to reduce the bioreactor N2O generation potential, in the context of minimizing total GHG emissions, in a hypothetical treatment facility where off-site electricity is produced by one of three primary sources: hydropower, nuclear and coal (no carbon capture/sequestration) that reflect primary electricity production in the Canadian provinces of British Columbia, Ontario and Alberta, respectively.