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Using plants as a filter to save Lake Winnipeg

By Amanda Lefley

Lake Winnipeg will get a little healthier after this spring.

A little less nitrogen and phosphorous will be entering Lake Winnipeg, two nutrients known to contribute to algae blooms, thanks to the Village of Dunnottar. Over the last two years the village has been running a pilot project with their sewer lagoon called a passive filtration system. After two seasons the results have reached the village’s goal; to increase the quality of water discharged into Lake Winnipeg. Decreasing nitrogen, phosphorus, heavy metals and fecal coliform content discharged from the municipality’s lagoon is what accomplishes this.

Because the pilot project has been a success, Dunnottar plans to use the data to design a full-scale passive filter for their lagoon. The biweekly tests from the pilot project have shown a decrease of nitrogen up to 60 per cent, while there was a reduction of phosphorus up to 62 per cent. Construction of the full-scale model is slotted to start this spring.

“This is designed to go on the tail end of lagoons,” explained Dunnottar Mayor Rick Gamble.

Overall, there are seven benefits that were achieved through the pilot project, which was developed by Dunnottar in partnership with Dillon Consulting Limited. The benefits include reducing pathogen (fecal coliforms) counts, toxin and heavy metals absorbed by suspended soils, and recaptured phosphorous for agriculture use, to name a few.

How it works:

The passive filter is made up of two cells, which essentially mimic the process of a natural wetland. There are plants bedded into sand, gravel and rocks in the cells that are the filter. Wastewater is discharged from the lagoon’s cells through the passive filter, where nutrients and contaminants are removed. They are trapped and used by the plants. Nitrogen, specifically, is processed by bacteria and released into the atmosphere in the form of N2 gas.

The filtration system has no energy inputs and no chemical additives, meaning it is all natural.

“It is an old technology that goes back many years. They used to use the waste from rolling mills, like the rolling mills in Selkirk, use the steel waste to attract the phosphorus. Phosphorus will attach itself to metal. In this day and age that doesn’t work anymore… Basically, we took the concept of an old technology and put all natural products into it for filtering the wastewater,” said Gamble.

What’s next:

Gamble explained the Lake Winnipeg Act has prompted every community to reduce the amount of phosphorus discharged into Lake Winnipeg by 2016. This passive filtration system will help achieve that goal for Dunnottar, although they were already starting the initiative before that legislation.

“When it comes to Lake Winnipeg one of the biggest problems with the algae blooms and the toxic algae blooms is the toxic is basically too much phosphorus being released into the lake,” said Gamble.

“We’ve been working for a number of years to clean up our own back yard so to speak.”

The full-scale system is expected to cost $500,000, and to Gamble’s knowledge currently engaged in this type of project.


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