Scientists testing sustainable P reclaimed from waste

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Phosphorous recycled from human and animal waste for plant fertilizer could ease demand for the dwindling, increasingly expensive rock-mined element.

Scientists at Washington State University have found plants flourish with struvite, a material in waste composed of magnesium, nitrogen and phosphorous. Teamed with Multiform Harvest, a Seattle phosphorous recovery company, the researchers are fine-tuning the application and amounts of fertilizer in hopes of marketing a product and benefiting the world’s food supply.

"You can’t continue mining a finite resource forever,” said Rita Hummel, a scientist at the WSU Puyallup Research and Extension Center. "But as long as we … can reclaim struvite from animal manure and sewage, then this is something that’s sustainable.

We’re figuring out how to use it effectively and safely.”

Benefits to local economy, water quality

Hummel is using Multiform Harvest struvite from wastewater treatment plants at Yakima, Wash., and Boise, Idaho. In addition, struvite from manure at dairy farms could result in development of regional nutrient recycling.

"When you feed a cow, about 20 to 25 percent of the phosphorous the cow eats ends up in the milk carton,” said Joe Harrison, Hummel’s scientist colleague at WSU. "That means about 70 to 85 percent doesn’t end up in the milk carton and ends up in the manure.”

Not only could reclaiming struvite from waste localize production and distribution, but it could also help mitigate water pollution problems such as overloading phosphorous in agricultural soils.

"The research being performed at WSU is central to us generating the hard data we must have to get this recycled phosphorus into the agricultural market, from large fields to specialized greenhouses and nurseries,” said Kevin Fullerton, product developer for Multiform Harvest.

Encouraging results

In previous greenhouse crop studies, Hummel discovered she could grow plants with struvite just as well as with the commercial phosphorous source, triple superphosphate. Crops like basil, cucumber, marigold and tomatoes barely sprouted without phosphorous, but flourished with struvite from King County municipal wastewater.

With support from a U.S. Department of Agriculture small business innovation research grant, she will experiment with different rates and ways of applying the struvite—adding it to the potting mix, sprinkling it on the surface or placing it beneath the plant—and looking at how quickly it is released.

"One of the things we need to look at here in the Puget Sound is if this is slow-release,” Hummel said. "We think it is and (we) are very interested in a slow-release product so it doesn’t leach out the bottom of the pots, run down the drain and into the streams, rivers and Puget Sound.”

Hummel is also interested in researching how the product interacts with Douglas fir potting mixes popular in the Pacific Northwest.

Variety of products

Most phosphorous in the U.S. comes from Florida. But U.S. production could decline sharply in the next 30 years, Fullerton said. Then the world will depend mainly on stockpiles in Morocco, China, South Africa and Jordan.

With the federal funding and WSU research, Multiform Harvest would use anaerobic digesters to recycle waste into crystalized solid fertilizer, providing growers with products like earth spikes, mixes and tablets that release nutrients.

"If we can take … a waste disposal problem and turn it into a fertilizer that actually replaces something we have to mine and are running out of - that’s sustainability,” Hummel said.

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