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Climate: the effect on grit

Grit removal is important to any wastewater treatment plant, as the cost of grit that accumulates in downstream systems is significant. But climatic factors may place an additional load on the plant, and under those circumstances effective grit removal becomes critical to maintaining operational effectiveness.

Take Calgary as an example. With over a million inhabitants it is the largest city in Alberta and the third largest in Canada overall, and its position on the confluence of the Bow and Elbow Rivers means that flood events are a regular feature, and—as the climate changes—may be intensifying.

Warm dry summers produce large amounts of wind-blown dust and sand, and in the severe northern prairie winters heavy ice and snow are frequently interrupted by warm Chinook winds that sweep up from the south as the Arctic fronts temporarily retreat, resulting in rapid thaws that can leave the streets awash with runoff full of the grit and sand used in winter road safety.

While much of Calgary’s sewerage comprises sanitary sewer, significant portions of the old sewers are combined stormwater and sanitary systems. Under the local climatic conditions the collected wastewater leads to high concentrations of grit in the raw sewage, as well as a large amount of additional grit carried in highway runoff.

A one-size-fits-all approach to grit removal is rarely appropriate even when climatic conditions are benign, but when they present additional challenges wastewater treatment plant operators should take a more holistic approach in order to deliver the most effective grit removal technology.

Read the Calgary case study.

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