Canadian Consulting Engineer

Duffin Creek sewage plant ordered to reduce phosphorous

May 11, 2016


The town of Ajax, east of Toronto, has applauded Ontario’s Minister of Environment and Climate Change for ordering the Regions of York and Durham to prepare a phosphorus reduction action plan over the next nine months for the Duffins Creek Water Pollution Control Plant.

The sewage treatment plant in Pickering on the shores of Lake Ontario receives piped waste from the growing regions to the north. To accommodate the increased flows the plant was expanded from a capacity of 420 ML/d to 630 ML/d a few years ago.

Since then the city of Ajax has blamed the effluent from its outfall for causing unsightly piles of blue algae on beaches in the area.


Others, like the Region of Durham, point out that high algae is present for most of the Great Lakes Shorelines and is caused by a number of factors. They say the phosphorous that encourages algal growth comes from many sources, including agricultural and urban run off. Invasive mussels could also be a cause. The Duffin Creek plant is one of the few plants that only releases highly treated effluent into Lake Ontario, and it does so through an outfall that extends a kilometre into the open water.

However, on May 4 the Town of Ajax issued the following statement, which read:  “The Order [from the Minister] is an important first step in recognizing the role of the WPCP [Duffin Creek plant] in causing excessive algae growth along the Ajax nearshore. The Order also shows a willingness by the Minister to consider options to optimize the WPCP operations to protect the Town’s waterfront.

“One of the main requirements of the PRAP [phosphorous reduction action plan] is to determine how phosphorus in the WPCP effluent can be reduced to the lowest achievable level for both current and future operating considerations. The Town has been studying this issue for the last three years, and has identified a preferred phosphorus removal technology (ballasted flocculation) that would eliminate the algae problem. The Town hopes this technology will be part of the PRAP assessment.

“Based on the Town’s scientific research, the amount of phosphorus in the WPCP effluent should not exceed 0.084 mgTP/L. This target is consistent with the level being required by the Minister for the Region of York at the proposed water reclamation plant being considered for the Upper York Sewage Solutions service area. The Town views the proposed target of 0.35 mgTP/L in the Minister’s Order as a short-term goal that will not improve the current algae problem.”

The statement continues, “The Town is looking forward to finding and implementing a solution to the algae growth along the Ajax waterfront.”

To read a fact sheet about the plant from the Region of Durham, click here.

To read the full Town of Ajax press release, click here.


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