The City's Wastewater System Division is responsible for the collection and treatment of the City's wastewater. The wastewater system consists of approximately 113 kms of wastewater collection piping of various sizes, 12 pumping stations and a Conventional Activated Sludge Secondary Treatment Wastewater Plant. In addition to maintaining the collection system and ensuring the wastewater treatment plant is operating within strict government regulations, wastewater staff is also responsible for enforcing the City's Sewer Use By-law, abatement sampling and public education.
Wastewater that leaves all homes and businesses in the City travels through a series of underground collection pipes to one of our 11 remote Pumping Stations. From there it is pumped to the Main Pumping Station at Centeen Park and then pumped to the Wastewater Treatment Plant. The Wastewater Systems Division maintains all of the above mentioned Pumping Stations and all underground wastewater collection piping from the property lines to the Wastewater Treatment Plant.
The public can do their part to help keep unwanted items out of the sanitary collection system to avoid costly repairs or blockages. Items like wipes, feminine hygiene products and fats, oils and grease should not be put down the toilets or drains. Open the links below to see what you can do to help prevent blockages in the collection system:
Upon arrival at the Wastewater Treatment Plant the wastewater is screened to remove large materials such as paper and plastics. Grit and heavy inorganic solids are also removed at this point in the treatment system. The wastewater continues to flow through to the primary clarifiers where a portion of the organics is settled out as primary raw sludge. Grease in the wastewater is also removed at this point in the treatment process. The primary raw sludge and any accumulated grease removed during this point of the treatment process are then pumped into our anaerobic digesters.
The wastewater flow leaving the primary clarifiers is called primary effluent. This primary effluent then flows to the aeration tanks where it mixes with Return Activated Sludge (RAS) and is then referred to as Mixed Liquor. The aeration tanks consist of an anoxic zone followed by the aerobic zone. It is in the aeration tanks that the microbiological population present removes contaminants such as Phosphorus, BOD and Ammonia. The aeration tanks are continually supplied with an appropriate amount of dissolved oxygen to keep the microbiological treatment process active.
The biologically treated Mixed Liquor is then directed to the circular secondary clarifiers where the majority of the solids are settled and returned to the beginning of the aeration tanks through RAS pumps. Just prior to the biologically treated mixed liquor entering the secondary clarifiers Aluminum Sulfate is injected into the stream to aid in the removal of additional phosphorus during this settling process. The wastewater flow is now referred to as secondary effluent as the treated wastewater flows over the weirs of the secondary clarifiers and travels on its way to the final step in the treatment process disinfection. Ultraviolet radiation (UV) is the disinfection process utilized before the final effluent is released to the receiving stream, the St. Lawrence River.
In addition to generating primary raw sludge the secondary treatment process also generates secondary sludge called Waste Activated Sludge (WAS). The WAS is sent to our Rotary Drum Thickeners (RDT's) prior to being pumped into our anaerobic digesters. The anaerobic digesters are responsible for reducing the amount of sludge solids generated during the treatment process prior to disposal. A byproduct of the digestion process is the production of digester gas. This digester gas is utilized at the wastewater treatment plant by our heating systems. The digested solids are processed through a centrifuge. This process creates a liquid called Centrate which is discharged back into the treatment process and Cake which is a solid product that is transported off site for disposal.
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