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Steel-making byproduct used as field tile filter

Conservation authority hopes to perfect farm-scale system for slag

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At farms in South West Oxford and Lucan Biddulph, a byproduct of the steel-making process is being inserted into tile drainage systems, as part of a research project by the Upper Thames River Conservation Authority (UTRCA) aimed at removing phosphorus from field runoff.

Members of the UTRCA board of directors saw one of the slag filter sites up close on Nov. 26, as part of a tour around the watershed.

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Why it matters: Elevated phosphorus loads in the Lake Erie watershed have led to algae blooms, and various agencies have devoted significant resources to decrease the amount of phosphorus entering streams from agricultural lands.

Agricultural soil and water quality technician Mike Funk said the project’s aim is to perfect a design that will make it possible for farmers to manage the system on their own without help from the conservation authority or other specialists.

The system viewed by the board of directors will be installed on the MacFarlane family’s cash crop and beef farm on Stonehouse Line. The other installation will be on the de Bruyn family’s hog farm in South West Oxford.

In both cases, it’s at the edge of a field (one 25 acres, the other about 30 acres) with an existing tile drainage system, and with an open municipal drain nearby.

In both cases, two of the filters will be installed for comparative purposes: one inside a three-foot pipe and the other inside a two-foot pipe. The MacFarlane farm has significant slopes; the de Bruyn farm is on flat ground.

The pipes, about 12 feet long, will be installed vertically near the tile outlet. The steel-making byproduct, called slag, will be loaded into specially designed bags and lowered into the pipe. The entire installation will be capped.

Funk showed a sample of the slag. It’s granular, with particles ranging from a 16th of an inch to a quarter of an inch and uniformly dull grey in colour. But Funk pointed out flecks of orange in the grains, and said these are the binding sites for the phosphorus.

“There’s a high iron content” in the slag, Funk said, adding the orange indicates rust on the exposed iron. “And the iron is what is going to chemically bind to the phosphorus in the water.”

Mike Funk and Tatianna Lozier, both agricultural soil and water quality technicians, helped conduct a recent tour of water quality conservation sites for the board of directors of the Upper Thames River Conservation Authority.
photo: Stew Slater

UTRCA’s Manager of Conservation Services Brad Glasman first saw a slag filter for agricultural runoff in action several years ago in Chatham-Kent as part of a collaboration between the Lower Thames Region Conservation Authority and the Ontario Ministry of Agriculture, Food and Rural Affairs.

The large installation containing several tonnes of slag left him wondering how this innovation could be adapted for applications beyond researching whether or not it worked to decrease phosphorus load.

Glasman glances at the notebook in one reporter’s hand, and recalls sitting down with Bluewater Pipe owner Tony Kime — whom he works with on the Thames River Phosphorus Reduction Collaborative. “We just had a notebook like that, and we started jotting down ideas.”

He says they “wanted to keep it at a size and a cost that farmers might be able to handle. We came up with a dollar value. Tony said it can’t be more than $1,000.”

With a smaller amount of slag available, as much as will fit inside the bag that gets lowered into either the three-foot or two-foot pipe, the amount of exposed iron in the slag is correspondingly limited.

The UTRCA was aware of this limitation, so part of the goal of the research is for the farmer to know when all the phosphorus-binding sites have been used up. If the system works as Glasman envisions, it would then be time to pull out the bag of slag with a front-end loader, refill it and then replace the filter.

“Part of the project is testing how long the slag material lasts before it’s ‘full’,” Funk said.

The UTRCA will also look into whether or not the slag can be “cleaned” in some way so the iron once again becomes available as a binding site.

As well, they’re monitoring how effective the filters are in decreasing the phosphorus loads in streams within the Lake Erie watershed.

The slag, says agricultural soil and water quality technician Tatianna Lozier, has been tested for other impurities or contaminants, and declared safe for use on fields or as aggregate on laneways. Slag from the steel-making industry has already been used in similar applications for many years.

According to Funk, at low flows, these filters will be capable of handling 100 per cent of the drainage off the field. But the sites have been designed so that, at peak flows, there will be a bypass directly into the municipal drain, “which is pretty typical of any treatment system you might put in.”

About the author


Stew Slater

Stew Slater operates a small dairy farm on 150 acres near St. Marys, Ont., and has been writing about rural and agricultural issues since 1999.



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