Atmospheric Emissions Associated with the Use of Biogas in Ontario

Abstract

This study aims to quantify the atmospheric emissions associated with an energy-from-waste transition in Ontario. Specifically, it explores the emissions from using livestock and food waste to produce biogas as a source of renewable natural gas. Biogas is one potential “closed loop” solution to waste management; however, there is potential for additional emissions associated with transitioning to anaerobic digestion as a waste management strategy. Each step along the anaerobic digestion process, from the transportation of feedstock to the storage of post-processed digestate, can release both greenhouse gas (GHG) and air pollutant emissions. Here, we quantified the net effects on emissions of a biogas transition in Ontario. We evaluated scenarios using up to 100% of available waste feedstocks in the province and compared these emissions to conventional manure management and landfilling. We found that emissions from current manure management strategies dominated GHG emissions, and, as more manure was utilized in the biogas system, there was a drastic decrease in corresponding emissions of CH4, N2O, and CO2, all of which are potent GHGs. All scenarios showed emission reductions compared to the traditional practice. By the 75% biogas scenario, GHG emissions associated with the biogas process are balanced by the potential offsets from avoided synesthetic fertilizer production, leading to negligible net GHG emissions from this system. In the 100% scenario, we observed SOx, VOCs, NH3, and PM2.5 were increasingly offset by emissions savings in the natural gas production and synthetic fertilizer production. The important exceptions were the significant NH3 and PM2.5 emissions associated with conventional manure management. Due to this, we did not see net emissions savings from the biogas scenarios until the 100% run. These results highlight the atmospheric impacts of conventional waste management and demonstrate the potential for anaerobic digestion to mitigating these emissions.