A Calgary Wastewater Treatment Plant Finds Real-Time Information on Effluent Quality Critical to Achieving Consistent Performance in Biological Nutrient Removal

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Courtesy of ASA Analytics

In 1994, the Bonnybrook Wastewater Treatment Plant in Calgary, Alta., completed the first phase of an upgrade to biological nutrient removal (BNR) after several years of testing.

Bonnybrook was not the first treatment plant to upgrade bioreactors for nutrient removal: Other communities had struggled with the technology. Bonnybrook operators determined that real-time information on final effluent quality was important to the BNR processes and installed online process analyzers to provide the data they needed to manage the plant.

A decade of use affirmed that the analyzers were critical to successful BNR operation. Paul Do, senior process engineer, was deeply involved in the BNR design and implementation and in the decision to install the ChemScan process analyzers from ASA Analytics.

With the analyzer, ,:We obtain real-time and instantaneous indications of the plant's final effluent quality, including TSS, ammonia, soluble phosphorus, nitrate and nitrite,' says Do. 'Knowing the instantaneous final effluent quality, we can immediately take corrective process measures to improve process performance and final effluent quality.'

BNR comes of age
The Canadian government estimates that 25 percent of all water body contamination is nutrient-related. That has led to increasingly strict wastewater effluent limits for phosphorus and nitrogen. To remain in compliance while operating with constrained budgets, more operators are evaluating upgrades to BNR bioreactors.

BNR has come of age for various reasons. Coagulants such as calcium, aluminum and iron have become more expensive for treating wastewater from growing populations. BNR also produces less biosolids in a form more conducive to land application. In addition, a public that favors green technology perceives biological processes as friendlier to the environment.

BNR technology was in its infancy when Alberta Environment established new stringent effluent limits and forced treatment plants to meet a phosphorus discharge of 1.0 mg/l. Instead of launching a full-scale conversion, Bonnybrook tested BNR on a limited scale while continuing to rely on its tried and true method of precipitating phosphorus with liquid alum.

Calgary, Alberta's largest city, was seeing steady growth that affected the operations of its two wastewater treatment plants. Bonnybrook's chemical costs were steadily increasing — in 1985 they approached $2.6 million and were forecast to reach $3 million within seven years, when the city population reached one million.

Controlling costs was a primary reason Calgary invested in BNR. Today Bonnybrook (design capacity of 132 mgd) is the largest BNR plant in Canada and the largest cold-weather BNR plant in the world. It treats an average daily flow of 111 mgd, operating 10 state-of-the-art BNR bioreactors that employ biological phosphorus and nitrogen removal processes. Specifically, the plant uses the A2/0 BNR process with return activated sludge renitrification.

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