Evaluation of GHG Emissions from Biosolids Stabilization and End Utilization Alternatives for the Capital Regional District

A part of the planning effort for two green field secondary treatment plants that will service the Core District of Victoria, British Columbia, a modified triple bottom line analysis was conducted to identify technologies that meet the Province's goals of cost effective, environmentally sustainable socially responsible wastewater treatment. One element of this analysis was to evaluate the impact of a combination of solids stabilization and end use alternatives on the net greenhouse gas (GHG) emissions of the future utility. If managed appropriately, biosolids production and utilization is a way to offset emissions from wastewater treatment operations and accrue carbon credits. Long-term benefits to Capital Regional District (CRD) include compliance with municipal carbon neutrality goals as well as potential revenue from the development of carbon trading markets.Analysis revealed significant carbon credits could be achieved with sludge stabilization by anaerobic digestion and biosolids utilization in mine reclamation. The greatest reduction in GHG emissions was achieved when the biogas from digestion was cleaned to natural gas line quality for introduction to the commercial grid. Co-generation proved to be less beneficial due to the low GHG intensity of the commercial power source available in the region. Additional carbon credits are obtained from mine reclamation due to improvement of soil productivity and carbon sequestration potential. However, it was also found that all of the end uses which capitalized on either the fertilizer value or energy content of biosolids can provide significant benefits to a wastewater utility.Results of this analysis enabled the CRD to make an informed decision about how to produce and use biosolids to maximize benefits from a sustainability perspective. However, it should be noted that the findings of this study are contrary to other studies in the published literature. This is attributed to the low GHG intensity associated with the power utility in the region (0.000022 tonne-CO2e/kWh). This observation suggests that utilities and engineering practitioners should be conducting site specific inventory analysis and use great care when evaluating literature reported results to make process decisions.