What are Biosolids?
Biosolids may be described as a nutrient-rich material that results from the biological treatment of municipal wastewater. Biosolids are generated in liquid form and typically have a solids content of
approximately 2 to 4%. The material may be further mechanically processed to remove water, to make
the remaining dewatered biosolids into a cake like material containing about 25 to 30% solids, making it
amenable to a number of management methods.
The City owns and operates four wastewater treatment plants. Treated effluent from the three largest plants is discharged through long outfall pipes into Lake Ontario. Effluent from the smallest plant,North Toronto Treatment Plant, is discharged into the Don River, which eventually flows into Lake Ontario. The treatment of wastewater generates a residue, referred to as sludge. The sludge is mostly organic in nature, with high nutrient value, in terms of phosphorus and nitrogen. Currently at the City’s wastewater treatment plants, sludge is further processed to stabilize the organics and reduce pathogen content. The stabilized sludge is referred to as biosolids. The City treats over 1.3 million cubic metres of wastewater every day and generates approximately 174,000 wet tonnes tonnes of wastewater
biosolids every year.
Currently, the City’s biosolids management options are landfill, incineration and beneficial land application as a fertilizer. See more information on biosolids and the wastewater treatment process.