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New Filter Removes P From Water

“It’s affordable to point where we think individual farmers could run it.”


When farmer and longtime conservationist Gordon Orchard first heard about a relatively simple process for removing dissolved phosphorus from water he thought it was too good to be true.

After all, there’s no disputing there’s too much of it in Lake Winnipeg. That’s why the Manitoba government is introducing a myriad of regulations aimed at farmers, municipalities and even individual homeowners.

Compounding the problem is that an estimated 18 per cent of phosphorus in the lake comes from the natural environment – mostly decaying plants and wildlife excrement – making it almost impossible to curtail and adding to the pressure to cut other sources of loading.

Orchard wasn’t alone. Researchers working with the Deerwood Soil and Water Management Association to reduce the phosphorus farming adds to runoff water were not only surprised but skeptical when first introduced to the process developed at Ontario’s University of Waterloo in 1995. The process uses a chemical reaction to pull phosphorus out of water and attach it to limestone.


In a telephone interview Scott Inwood, the university’s director of commercialization for the Intellectual Property Management Group, said several commercial filters have been installed at lake campground washrooms in Ontario. The Toronto suburb of Richmond Hill is considering the system to remove phosphorus from an entire lake, albeit a small one, Inwood said.

The university has also developed a process to remove nitrogen from water and kill waterborne bacteria such as E. coli, providing a complete wastewater nutrient management system that runs virtually on its own. Pumps aren’t required as the system is designed so the water being processed runs downhill.

“It will run automatically,” says Robert Gervais, president of Agassiz Enviro-Systems Inc., the Manitoba company licensed by the University of Waterloo to install the system in Western Canada.

“These systems are working in our test trials 98 per cent efficient,” Gervais says as he takes a break while installing the system to treat runoff water collected from Orchard’s cattle yard. That means untreated water that exceeds Canada’s guidelines for phosphorus has just trace amounts after going through the filter.

Agassiz Enviro-Systems is helping to cover the cost of the installing the University of Waterloo’s “Phosphex” and “Nitrex” filtering system here to demonstrate how effective it is. The Manitoba government is also providing some funding, as is the Pembina Valley Conservation District.

Agassiz Enviro-Systems is also setting up a smaller demonstration system to treat effluent from the Village of Miami’s sewage lagoon.

While the system is very good at capturing phosphorus and nitrogen from livestock waste, it’s especially well-suited for doing the same with effluent from towns and small cities, he said.

“Of course the larger the project the lower the per unit cost,” says Gervais. “It’s affordable to point where we think individual farmers could run it.”

Inwood agrees. “It represents a significantly cheaper option than putting in expanded wastewater treatment,” he says.


Small cities and towns in Manitoba aren’t required to remove nutrients from their wastewater. However, municipal sewage must be treated for bacteria. Most rely on sunlight shining on their lagoons to do that. As towns grow, they need to build more lagoons, which often requires purchasing more land. In some cases installing the University of Waterloo’s system would be cheaper, less malodorous and have the added benefit of removing nutrients.

How does the technology work? Magnesium oxide, a fine dust created in oxygen furnaces during the steel-making process, is mixed with water and limestone. Water runs through the coated limestone and a chemical process takes the dissolved phosphorus out of the water and it sticks to the limestone. The filter is effective for 10 to 15 years. When the limestone no longer absorbs phosphorus, it’s removed and replaced.

Most of the spent limestone is used to make concrete, essentially removing the captured phosphorus from the environment – forever.


While that sounds appealing given phosphorus has such a bad reputation as a pollutant, Don Flaten, a soil scientist at the University of Manitoba, suggests caution.

“Remember every living organism on the planet needs phosphorus, including humans,” he says. “There is no substitute for phosphorus in the human diet. If and when we run out of phosphorus we’re done. It’s not like gasoline and diesel fuel and natural gas where you can find alternatives. If we take all of our excess agricultural phosphorus and tie it up in concrete, future generations will wonder why we were that stupid.”

Flaten isn’t totally opposed to the phosphorus filter technology. It could be used as an “emergency measure,” he says.

“My priorities as a researcher are to try and promote schemes that recycle and ideally reduce phosphorus loss in the first place at the source rather than intercepting it.”

Filters will never come close to removing all the world’s phosphorus, Inwood says. Meanwhile, studies are underway to see if the phosphorus-laden limestone used in the filters can be spread on farmers’ fields as a form of slow-release phosphorus fertilizer. If so, the University of Waterloo’s process will be “the perfect green technology,” Inwood says.

“It’s taking a byproduct from the steel industry and using it in a process that is remediating a contaminate in the natural environment and then recycling it back into a feedstock for the agriculture community. It’s green, green, green all the way round.”

Flaten is skeptical. Any chemical process so efficient in removing phosphorus molecules from water isn’t going to release it easily, he says.

As for treating sewage, Flaten advocates removing phosphorus through biological processes, rather than chemical, so the captured nutrients can be recycled.

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About the author


Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.



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