CALGARY'S LONG TERM BNR STRATEGY SIGNIFICANTLY REDUCES CHEMICAL COSTS

This paper describes the implementation of biological nutrient removal technology at the City of Calgary's wastewater treatment plants between 1989 and the present. Prior to 1989, the City met the effluent total phosphorus limits at its two wastewater treatment plants through in-plant alum addition. Two modules of the Bonnybrook WWTP, with a capacity of 400 ML/d, were sequentially retrofitted to biological phosphorus removal and nitrification. A separate new module, with a capacity of 100 ML/d and designed for optimal biological phosphorus and nitrogen removal, brought the total plant capacity up to 500 ML/d, making the Bonnybrook WWTP one of the largest BNR facilities in North America, and possibly the largest cold-weather BNR facility in the world. The resulting savings in chemical costs are estimated to be more than CDN 3.5 million (US 3.1 million) per year. Details are also provided of a new 100 ML/d state-of-the-art BNR facility that is currently under construction to serve the rapidly growing south and southeast areas of the City.