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Phosphorus recovery can complement source reduction

Globally, it's estimated that one-third of all phosphorous applied is lost to water due to erosion, leaching and run-off

A Manitoba engineer says phosphorus (P) recovery methods can be an important addition to the province’s phosphorus management strategies.

Francesco Zurzolo, an engineer specializing in nutrient management and reduction with Dillon Consulting, says Manitoba is dealing with eutrophication and destruction of important ecosystems due to P buildup. Zurzolo spoke at the Manitoba Environmental Industries Association’s (MEIA) annual Emerging Issues conference in Winnipeg on November 19.

“The basic question is, where is this phosphorus coming from and what can be done about it?” he asked.

Lake Winnipeg carries a P load annually of 7,655 tonnes, with the Red River its biggest “loading factor,” contributing 68 per cent of the annual total load, said Zurzolo. At least 80 per cent of the nonpoint source load — or pollution discharged from a wide land area rather than a specific location — is run-off from agricultural soils.

“Globally, it’s estimated that one-third of all P applied to land is lost to water due to erosion, leaching and run-off,” said Zurzolo, citing a 2009 study.

In Manitoba, the recent surge of nutrients, especially P, to Lake Winnipeg is due to the flooding cycle of the last decade, with P moving as a particulate and dissolving in flooding events, he explained.

Management

Manitoba’s Water Quality Standards cap P at one milligram per litre. In addition, producers must follow P application rates for fertilizer and manure, and are required by Manitoba Conservation to test soils prior to manure application.

Zurzolo said source reduction is the best method for reducing P loading. “The best technique is to avoid applying too much phosphorus to soils in the first place,” he said.

Zurzolo said one way to address diffuse sources of P run-off, such as cattle operations, is source reduction. This can be achieved by reducing the amount of excess P on soils.

One method involves manure treatment through dewatering, drying, composting or direct P recovery through struvite removal.

Another technique is sedimentation, or particulate P recovery. Sedimentation involves the use of stilling basins along drainage routes to allow particle settling, followed by occasional dredging for particle recovery.

This method can sometimes require the use of land area currently used for crop production, said Zurzolo. “But the loss of a small amount of land to crop production is a small price to pay for the health of our freshwater ecosystems. These structures have been found to reduce flooding and they’re good for drought years,” he said, pointing to the success of the Tobacco Creek Model Watershed.

Another method involves filtration for particulate and soluble P recovery. “Dillon has re-examined an age-old design of the “passive filter” concept which combines physical and chemical removal processes,” he said.

Partnering with the East Interlake Conservation District, which offers programs and funds for projects that improve the health of Interlake watersheds, the company has developed a project on one cattle operation to help a farmer utilize a detention basin to remove organics and particulates through a filtration system.

“It’s a low-cost solution and very robust,” said Zurzolo. “These are the kinds of solutions we need to start looking at around the province.

“We need to combine source reduction and runoff management to come up with a proper solution,” Zurzolo concluded. “The concern I want to leave with you is that right now the big money is being spent on point sources, but we need to increase funding to look at diffuse sources of phosphorus reduction and recovery. We need to incorporate P recovery considerations for all projects. Reducing the need for P imports will contribute to a healthier lake.”

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