Stantec is prime consultant for the City of Calgary, Alberta, to complete upgrades at the Bonnybrook wastewater treatment plant, which will be one of the largest cold-weather biological nutrient removal (BNR) sites in North America. The scope of work for the $575-million Bonnybrook project includes increasing treatment capacity for three existing secondary treatment plants and a full expansion of a fourth plant. When complete, the total capacity will be 150 mgd for average flows, 402 mgd peak, providing treatment for a population of 1.37 million people. Biological activity slows when wastewater temperatures are low, presenting challenges in the BNR process. As a result, the design team adjusted the sizing of aerobic bioreactor tanks and secondary clarifiers to increase the solids retention time during colder months. The project is being delivered in a construction management-at-risk model, with the scope divided into 16 construction packages and eight major equipment preselection packages. Currently, primary treatment, secondary treatment, ultraviolet upgrades, outfall, biogas handling, cogeneration, MCC upgrades and flood-protection projects are under construction. Construction began in 2016 and is expected to be completed in 2025.

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