Generating biogas through the co-digestion of municipal organic waste and sewage biosolids at the Cornwall Wastewaster Treatment Plant

The City of Cornwall will partner with the Ontario Clean Water Agency (OCWA) to explore opportunities to generate biogas by co-digesting municipal organic waste with sewage biosolids at Cornwall’s wastewater treatment plant. The project aims to decrease the plant’s energy consumption through improved digester processes while increasing the amount of renewable energy the plant generates. It also aims to divert waste from landfill, as Cornwall currently sends its treated sewage biosolids to landfill. The city also anticipates that the project will decrease the plant’s operating costs while improving its overall performance. The co-digestion of sewage biosolids with other forms of organic waste (e.g., source-separated organics) is expected to increase the rate and volume of biogas production at the plant. The study will explore the most economically feasible uses for that biogas. For example, some of it could be upgraded to renewable natural gas (RNG), which has an energy value equal to fossil fuel natural gas. The RNG could be used onsite or it could be injected into a natural gas pipeline. Greenhouse gas emissions and energy savings should result from three key elements of the project. First, by eliminating the need to transport sludge and organic waste to landfill, Cornwall will reduce its diesel fuel consumption. Second, improved digester processes will reduce the plant’s energy consumption. Third, the proposed approach will capture greenhouse gases (especially methane) that would otherwise be released by organic matter decomposing in landfill. The study will also explore the possibility of retrofitting the plant’s existing anaerobic digester to increase its efficiency and capacity. This could enable Cornwall’s plant to receive sludge and waste from surrounding plants, making it a regional facility. This project aligns with provincial policies focused on diverting food and other types of organic waste from landfill. Reducing greenhouse gas emissions aligns with the city’s official plan. The project also supports Cornwall’s broader goal of transforming its water pollution control plant into a net-zero resource recovery facility. Innovative aspects • The study aims to demonstrate the technical and financial feasibility of producing energy and a high-quality biosolid product from waste • The study will explore the needs of neighboring food industries, municipal wastewater treatment plants and septage haulers and look at options for generating extra revenue through the processing of these materials, possibly creating a regional facility that would generate revenue for Cornwall Replicability • The project team estimates that similar approaches to co-digestion and RNG production could be readily adopted by 30 wastewater treatment plants in Ontario and more than 50 plants across Canada • OCWA, the project consultant, will capitalize on its broad network in the Ontario wastewater sector to communicate lessons learned to municipalities across the province (Project description from original funding application)