How We Work

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Wastewater treatment is a complex process that removes or reduces contaminants, allowing it to be released as clean water (known as effluent) into the expansive North Saskatchewan River that spans from Banff National Park to Saskatchewan.

The wastewater is treated at the ARROW Utilities treatment plant using physical, chemical and biological processes. It undergoes final disinfection before the treated effluent is released to the North Saskatchewan River to protect the downstream communities that use the river for their drinking water and the aquatic organisms that call the river home.

Primary Treatment

The first step in the treatment process is a physical process that removes approximately 40% of the organic materials and 75% of suspended solids from the raw wastewater.

This is accomplished by first passing the incoming wastewater (influent) through a fine screen to remove large debris. Once through the screen, the wastewater flows into 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 settleable materials and separates the solids and grit from the water by a process called classification. The solids, grit and screenings are then disposed of at the landfill.

Once through the aerated grit chambers, the wastewater flows to the primary clarifiers. Here, the 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 pumped to the sludge fermenters, where the organic material is broken down. The carbon-rich volatile fatty acids (VFAs) by-products of this are a necessary component required in secondary biological treatment. The scum is sent directly to the digester, where it combines with the other process “waste” streams and much of the remaining organic contents are metabolized by anaerobic bacteria. Reducing the overall volume of sludge to be transported to the lagoons.

Secondary Treatment

Next, wastewater at the ARROW Utilities treatment plant flows through large, multi-celled tanks. In this treatment process, microorganisms present in the wastewater are utilized to remove the remaining organic material by means of Biological Nutrient Removal (BNR). In the BNR process, organic material, nitrogen and phosphorus are metabolized by the microorganisms at different stages and under different conditions within the bioreactor. It is this critical process that removes the harmful nutrients that, if discharged untreated to the river, could harm the aquatic life or cause algal blooms in the North Saskatchewan River. These algal blooms can deplete oxygen levels in the water to uninhabitable levels and can also prevent photosynthesis in plants below the water’s surface.

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 that allow the sludge to settle and be recycled back into the BNR process (known as return-activated sludge/RAS). The clear surface effluent flows over weirs and proceeds on to disinfection by UV treatment.


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

Digester Sludge (Biosolids) Treatment

The sludge that ends up in the digesters, also 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 boilers and hydronic heating system in the plant. The remaining digested sludge is hauled out to the Clover Bar 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.

Treatment Performance/Quality Assurance

The organization houses an on-site analytical laboratory operating 365 days a year. Accredited to the Canadian Association for Laboratory Accreditation (CALA) ISO 17025, the laboratory provides daily compliance testing on the final discharge mandated in the provincial Environmental Protection and Enhancement Act Approval No. 486-03-00 by Alberta Environment and Protected Areas. Our lab commits to supporting operations and engineering with real-time analyses of process samples to enable prompt adjustment and proactive measures to attain increased control over the treated water quality and treatment efficiency. The laboratory also supports source control to monitor the discharge received from industrial sites within the region.

The ARROW Utilities Wet Weather Strategy

Excess wet weather flow affects communities throughout the Alberta Capital Region, potentially causing their sanitary systems to become overloaded, leading to significant environmental, public health and financial impacts.

In 2014, ARROW Utilities adopted a Wet Weather Strategy for the region. The Wet Weather Strategy is the result of a two-year collaborative effort by ARROW Utilities and its 13 member municipalities. The adoption of the Wet Weather Strategy is a significant step toward addressing issues related to excess wet weather flow in the region.