Already a year ago, the Canadian biggest metropolis was opening its second anaerobic digestion plant, the Disco Road Organics Processing Facility, which can process 83,000 tons of organic residual waste annually. Moreover, Toronto’s first anaerobic digestion facility, the Dufferin plant, also benefits from a significant upgrade and will see its processing capacity jump from 25,000 to 55,000 tons of organic residual waste by 2018. These more important infrastructures became possible due to the experience acquired by running the Dufferin plant for 12 years.
The process in both facilities is optimized to accept the most diverse residual waste input. Using the BTATM Hydromechanical Pretreatment System, source separated organics are treated 16.5 tons at a time to remove contaminants like plastic bags, batteries, bones, glass, etc.
The resulting digestible organic matter is then stocked in a tank before being introduced into the digester. The stocking tank allows a 24/7 regular inflow to the digester, yielding a steady biogas output of approximately 110 m3 per ton of digestible organics.
In 2015, almost half of the biogas produced was used to heat the digester tanks. Part of the remaining biogas planned to be used to generate most of the electricity needed by the facilities to operate, which will be potentially self-sufficient in the future.
Toronto is also exploring other eventual possibilities for this biogas production, such as selling electricity to the provincial grid, or refining it to biomethane and selling it to the natural gas grid or using it to fuel its municipal vehicles.
Toronto is able to feed these anaerobic digestion plants by engaging its citizens into the process. Therefore, the city distributes 45L “Green Bins” free of charge, mostly to single-family residences. Citizens are eased in by letting them include in the bin most non-organic waste, such as plastic bags that reduce odors, which are anyway removed in pretreatment decontamination.
Following is the weekly collection in two-bin garbage trucks that can collect a second type of residual waste, rotating between recyclables and garbage straight for landfill. Seasonal collection of green residual waste like leaves and grass, in paper bags, add up to the input. In the case of inflow overcapacity for the municipal facilities, source separated organics in excess are simply outsourced to private anaerobic digestion facilities.
A study by Recyc-Quebec conducted in 2014 showed that the city of Toronto has one of the best rates of recuperation of food residues among 28 regions of Eastern Canada, with an average of 180 and 215 kg recuperated per home per year. It seems obvious that Toronto is a great example of efficient large-scale municipal residual waste management.
Sources: BioCycle, BTA, Recyc-Quebec