How we treat wastewater

Wastewater comes from day-to-day activities like toilet flushes, showers, or laundry. The wastewater then goes down your drain, into our sewer system, and eventually to one of our three wastewater treatment plants. After treatment, the water is returned to our rivers and lakes.

Why we treat wastewater

Wastewater contains contaminants like nutrients and bacteria.

Phosphorus and nitrogen are nutrients found in wastewater. They can act as a food source for algae, fish, and other animals. Too many nutrients, phosphorous in particular, in a waterbody can lead to overgrowth of algae. Too much algae is unhealthy in water systems.

The City of Winnipeg is committed to reducing the amount of phosphorous we release to our rivers and lakes. In the past, we were contributing around four to five percent of all phosphorous in Lake Winnipeg. The remaining phosphorous comes from other sources in the watershed. After we finish the North End Wastewater Treatment Plant (NEWPCC) upgrades, we will be significantly reducing our phosphorous contribution.

Our wastewater treatment process

Wastewater treatment involves physical, chemical, and biological processes to remove solids, nutrients, and bacteria from our wastewater. The end product is water that is safe to return to our rivers and lakes.

The wastewater moves through several different processes inside one of our three wastewater treatment plants as described below:

Pre-treatment

Wastewater passes through screens to remove large items like rags and garbage. The wastewater then flows into grit removal tanks. In the tanks, solids like sand, dirt, and gravel settle to the bottom, allowing for easy removal. Removing these materials:

Decreases wear and tear on equipment
Lowers maintenance costs
Reduces downtime for repairs

Primary clarifiers

Next, the wastewater moves into large settling tanks called primary clarifiers. In this step, the solids are separated from the liquid:

The solids in the wastewater sink to the bottom. The settled solids are called sludge. This sludge and the oil and grease skimmed from the top of the tanks are sent to the next solids treatment step
The liquid stream, which makes up about 99 percent of the wastewater, overflows to the next liquid treatment step

After primary clarification, the solid and liquid parts of wastewater are treated separately.

The Liquid stream

After primary clarifiers, the liquid wastewater stream goes through further treatment processes including bioreactors, final clarifiers, and ultraviolet (UV) disinfection.

Bioreactor

Bioreactors are large tanks that mix wastewater and microbes. Microbes are bacteria, viruses, and protozoa which feed on carbon, nitrogen, and phosphorus removing it from the liquid wastewater. This creates a nutrient rich living sludge called activated sludge. Activated sludge and the liquid wastewater is then sent to the final clarifiers.

Final clarifiers

Final clarifiers separate the activated sludge and liquid wastewater. During this process, the activated sludge settles to the bottom of the clarifiers. The settled activated sludge is returned to the bioreactors. This helps to continue the treatment process in the bioreactor. The liquid wastewater goes to UV disinfection.

Ultraviolet (UV) disinfection

UV light is used to neutralize bacteria and viruses, like E.Coli and fecal coliform, in the liquid wastewater. UV lamps are submerged in the liquid wastewater, exposing it to disinfecting light for two to four seconds. Once the process is complete, the liquid wastewater is safe to release into the river.

At the West End Wastewater Treatment Plant, we use shallow outdoor ponds instead of UV lamps. In these ponds, the sun's natural UV rays disinfect the liquid wastewater. In the winter, treated wastewater is allowed to cool in the ponds before going into the river. This reduces the chance of thin river ice.

The Solid stream

After primary clarifiers, the solid stream goes through further treatment processes including digestion and dewatering.

Digestion

Solids from wastewater are treated in a tank called a digester. These tanks are anaerobic which means that they do not contain oxygen. This process reduces the volume of sludge.

Microbes in the digester, called anaerobes, feed on carbon in the solids. They produce carbon dioxide and methane gases. We collect the methane and use it to heat the digester and other buildings at the treatment plant.

Dewatering

After digestion, we remove excess water from the sludge by spinning it at high speeds in a centrifuge. The liquid produced during this process is called centrate. This centrate is further treated then sent back to pre-treatment.

The remaining solids are called biosolids. We use biosolids to fabricate soil or as fertilizers on farmer's fields.

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