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WWTP upgrades cut Grand River ammonia levels, UWaterloo study finds

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Five wastewater treatment plants (Waterloo, Kitchener, Preston, Galt and Paris) discharge directly into the middle section of Grand River, the largest and most populated watershed in southern Ontario discharging into Lake Erie. Photo credit: UWaterloo

A University of Waterloo team studied what happened to the health and metabolism of the Grand River’s ecosystem when the two biggest wastewater treatment plants in the area introduced nitrification treatment to reduce ammonia.

Five wastewater treatment plants (Waterloo, Kitchener, Preston, Galt and Paris) discharge directly into the middle section of Grand River, the largest and most populated watershed in southern Ontario discharging into Lake Erie.

Following the upgrades to the plants in Kitchener and Waterloo, there was a massive drop in the amount of ammonia going into the river, according to sensor data. Before the changes, the two wastewater plants discharged more than 90 metric tons of ammonia a month. In just one year, over 2012-2013, the Kitchener treatment plant reduced its ammonia release by 80%.

Helen Jarvie, University of Waterloo professor of water and global environmental change in the Department of Geography and Environmental Management, and Water Institute member, said that local investments in wastewater treatment are definitely improving water quality.

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“This is a great success story,” says Jarvie. “We have shown how investments in wastewater management have yielded important improvements to the ecological health and water quality of the Grand River.”

Her research, published in the Journal of Environmental Quality, explores the impacts of nutrients like phosphorus and nitrogen, from agriculture and wastewater, on water quality, including nuisance and harmful algal blooms.

One decade later, the total ammonia output at the two upgraded WWTPs has dropped to less than one metric ton a month, or a 99% decrease, the study found. Nitrogen was still flowing into the river, but it was now in an amount and form that is less problematic for dissolved oxygen levels and fish.

Jarvie’s team studied how this drop in ammonia from wastewater affected the river. Too much ammonia depletes oxygen, killing aquatic life. So, the Grand River Conservation Authority put sensors in the river to measure how these vital dissolved oxygen levels changed.

During the study, researchers discovered that on nearly 90% of summer days prior to the nitrification treatment, overnight oxygen levels dropped below the levels needed to support aquatic life. After nitrification treatment, nighttime oxygen dropped below levels needed to support the most sensitive creatures on just 6% of summer days.

“Ammonia is a nitrogen compound produced by the breakdown of organic matter in sewage,” explained Jarvie. “Discharge of ammonia into waterways can have direct toxic effects, but also cause significant oxygen depletion that threatens the survival of aquatic life, including fish,” she added.

The study’s authors said the research demonstrates the value of combining river metabolism with nutrient monitoring for a more holistic understanding of the role of nutrients in river ecosystem health and function.

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