Wastewater Process

Wastewater Transmission and Treatment for the Capital Region

The fourth-largest treatment facility in Alberta, our plant meets the wastewater and sewage needs of more than 200,000 residents within 13 municipalities in the Capital Region each day. The wastewater is treated to remove and reduce contaminants, allowing it to then be released as clean water into the North Saskatchewan River. The removal and reduction of contaminants is completed through the combination of physical, chemical and biological processes at the ACRWC wastewater treatment plant. Removing these contaminants results in the preservation of the aquatic environment of the North Saskatchewan River and the prevention of transmission of water-borne disease.

Following treatment at the plant, what started out as wastewater is discharged as clean water into the North Saskatchewan River basin and the aquatic ecosystem all the way to Lake Winnipeg and Hudson Bay.

Our Transmission System

The Alberta Capital Region Wastewater Commission (ACRWC) transmission system consists of 138 km of gravity sewers, ranging from 525 to 1,500 mm in diameter, 58 km of pressure pipelines (force mains) of 500 to 900 mm in diameter, and five pump stations. This pipeline network is longer than the distance from Edmonton to Red Deer!

This system conveys wastewater to the Capital Region Wastewater Treatment Plant from member municipalities in the west, north and east sections of the region. It also conveys wastewater from the south members (City and County of Leduc, and the Town of Beaumont) into the City of Edmonton system for treatment. In exchange, the plant takes wastewater from Clareview in northeast Edmonton and from the Clover Bar Industrial Area.

Our Wastewater Treatment Process

Wastewater treatment is a complex process that removes or reduces contaminants, allowing it to be released as clean water (known as effluent) into the North Saskatchewan River. The wastewater is treated at the ACRWC treatment plant using physical, chemical and biological processes. It undergoes a final disinfection before the treated effluent is released to the North Saskatchewan River in order to protect the downstream communities who use the river for their drinking water and the aquatic organisms who call the river home.

Primary Treatment

Primary treatment is the first step in treating the raw wastewater that reaches the plant. It is a physical process which removes approximately 40% of the organic materials and 75% of suspended solids from the raw wastewater. This is accomplished by passing the wastewater through a fine screen where large debris is removed.

Once through the screen, the wastewater is sent through an aerated grit chamber. In this chamber, air bubbles reduce the buoyancy of heavy solids and grit, causing them to settle to the bottom. Mechanical equipment collects the settled sludge and separates the solids and grit from the water. The solids and then disposed at the landfill.

Once through the aerated grit chambers, the wastewater is sent to the primary clarifiers. Here, remaining heavier particles are given an opportunity to settle and any leftover scum floats to the surface. Again, the settled sludge and floating scum are collected from the wastewater. The sludge from the primary clarifiers is sent to the sludge fermenter, then on to the digester.

Bar Screens
Aerated Grit Tanks
Primary Clarifier
Biological Treatment

After the primary treatment, wastewater at the ACRWC treatment plant is sent through biological treatment, which is the core treatment process. In the biological treatment process, microorganisms present in the wastewater are utilized to remove the remaining organic material in the Biological Nutrient Removal (BNR) bioreactors on site. In the BNR process, organic material, nitrogen and phosphorus are metabolized by the microorganisms. It is important that the microorganisms remove nutrients as the release of effluent with high nutrient concentrations could harm the fish species of the North Saskatchewan River and cause algae to grow out of control and create algal blooms. These blooms cause lower oxygen levels in the river which can create a toxic environment. Domestic wastewater typically contains approximately 35 ppm (parts per million) ammonia and 7 ppm phosphorus. Some industries may produce wastewater with high nitrogen and phosphorus concentrations.

The bioreactors are divided into several cells, each with or without air input to generate anoxic, anaerobic or aerobic conditions suitable for different species of bacteria to utilize organic materials and nutrients. Air is introduced into the bioreactors with a fine bubble aeration system.

Once through the BNR bioreactors, the wastewater passes through secondary clarifiers to separate the microorganisms from the treated wastewater.

Secondary Clarifier
Secondary Clarifier

Before the treated wastewater is discharged to the North Saskatchewan River, it is disinfected with ultraviolet light. This greatly reduces pathogenic bacteria levels in the treated effluent, making it suitable for recreational use.

UV light for final disinfection
ACRWC Outfall on the North Saskatchewan River
Sludge (Biosolids) Treatment

The sludge, known as biosolids, generated in the processes at the plant is anaerobically digested to reduce the organic components in the solids. This process results in the production of biogas which is mainly used as a fuel for the boiler and heating system in the plant. The remaining digested sludge is hauled out to the Cloverbar sludge lagoon for disposal. After the solids and liquid at the lagoon separate, the solids are used either as a co-composting material or as fertilizers.


Please click on the individual process links below for further technical information and diagrams on how they contribute to the treatment of wastewater at ACRWC: