Sewage Treatment Process & Collection System
Generally speaking, storm sewers (carrying rainwater) discharge to the St. Marys River or to a receiving water course that flows to the river.
In an area with municipal sewer and water services, anything that is flushed goes into pipes that cross the property (sewer laterals) and connect to the sewer main. The sewer main, located under the street surface, collects and carries wastewater to a treatment facility. Sanitary sewer mains flow into progressively larger pipes, by gravity and through pumping stations, until they reach one of two wastewater treatment plants. The east-end plant treats about two-thirds of the City's sewage, with the remainder being treated at the west-end plant.
Primary treatment of raw sewage entails fine screening, grit removal then clarification. In the clarification process, the screened wastewater is slowly directed through settling tanks where suspended solids naturally sink to the bottom. This sludge is then dewatered and sent to the landfill. Floating matter, such as grease, rises to the top and is skimmed off. The clarified wastewater then progresses to secondary treatment.
Secondary treatment removes organic materials and nutrients with the help of naturally occurring bacteria – the water flows to large, aerated tanks where bacteria consumes everything it can.
All wastewater contains significant levels of phosphorus and nitrogen that promote algae growth and consequently have a negative impact on lake or river water quality. The City's east-end Wastewater Treatment Plant was the first large-scale plant in Ontario to utilize a biological nutrient removal process to reduce nitrogen and phosphorus without the use of chemicals. The last stage of secondary treatment is final clarification or settling.
The third and final step in wastewater treatment is disinfection. At the east-end plant, this is achieved by ultraviolet light. Chlorination is used at the west-end plant. The disinfected water is then discharged into the St. Marys River through diffusers.
A copy of the
2023 Annual Sewage Collection System Report is available to review here.