Wastewater management in Guelph


Wastewater refers to anything you send down your drain or toilet; water, cleaners and chemicals, toilet paper, and human waste.

Everything and anything you send down the drain or toilet flows through the City’s sanitary sewer collection system to Guelph’s wastewater treatment plant where it is filtered, treated and released into the Speed River.

First, we use screens to filter out large pieces of debris for and send them to landfill for disposal. The filtered wastewater moves into clarifiers (or settling tanks) where material suspended in the water can settle to the bottom. After about two and a half hours we collect the settled materials (sludge) from the bottom, and skim fats, oil and grease (scum) from the top and send them to digesters for processing.

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What happens to the water

With the sludge and scum removed, the wastewater goes to an aeration tank where microorganisms consume any remaining organic waste suspended in the water. Microorganisms also need air to survive, so we add air to the tank using use aerators like the ones you see in aquariums.

After about nine hours, when the microorganisms have consumed everything they can, the wastewater flows to a final tank (secondary clarifier) where the microorganisms settle to the bottom. When the microorganisms are ready to consume more organic waste, we collect them from the bottom of the tank, and return them to the aeration tank.

The wastewater goes through sand filters to remove any tiny, remaining particles that may still be suspended in the water.

We add a small amount of chlorine to kill any harmful bacteria or germs that may remain in the filtered wastewater.

We know chlorine is not good for fish, plants and wildlife, so we use bisulphite to remove any leftover chlorine before we send the water into the Speed River.

What happens to the waste

We pump the sludge and scum from the first clarifier into digesters. Digesters work like stomachs; the anaerobic microorganisms that live in the digester consume bacteria and help reduce pathogens and odours to produce biosolids.

As the microorganisms consume bacteria, they great methane gas. We capture and use the methane to generate heat and electricity to help power the wastewater plant.

Learn more about generating electricity at City facilities

When the microorganisms consume most of the bacteria, we separate excess water from the biosolids and treat them using heat, alkali, and high shear mixing. Then the material is available for agricultural purposes, sod farming, golf courses, horticulture, forestry, reclamation & bioremediation.

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For more information

Monday to Friday 8 a.m. to 4 p.m.
[email protected]
After hours emergency: 1-866-630-9242