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UI Scientist Makes Plastic from Cow Manure

UI Scientist Makes Plastic from Cow Manure

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photo courtesy of UNIVERSITY OF IDAHO

Ph.D. student Nick Guho, right, and Erik Coats, associate professor of civil engineering at the University of Idaho, are seen in a mobile laboratory at the university’s research dairy in Moscow. Coats and Guho feed dairy manure to naturally occurring bacteria, converting the product to a biodegradable plastic known as polyhydroxyalkanoate or PHA.

MOSCOW, Idaho • Drive by a dairy and take a good whiff. Anyone in the industry will say “that’s the smell of money.”

Idaho is home to more than a million dairy cows, and each cow produces 100 to 150 pounds of wet manure every day.

“That’s a lot of manure,” said Erik Coats, University of Idaho associate professor of civil engineering.

Coats and his research group at the university have developed a way to generate a significant economic return from the dairy industry’s waste stream by converting manure into a biodegradable plastic.

“Our process uses the unique capabilities of naturally occurring bacteria to ferment manure and then convert the fermentation products to a plastic,” he said.

The process, which results in the compound polyhydroxyalkanoate, or PHA, is simpler than it sounds.

The various bacterial strains Coats uses is ordinary stuff found in the soil. He gets his biomass in bulk from wastewater treatment plants.

Coats ferments dairy manure in tanks, creating a slurry of organic acids similar to vinegar that he feeds to a bacteria.

The organisms feast on the fermented slurry, bonding carbon molecules inside their cells in the process.

“If we eat too much food on a regular basis, our bodies store the extra as fat,” Coats said. “If we feed bacteria too much, they store the extra inside their cells as carbon polymers.”

After the millions of bacteria bulk up up on the fermented slurry, Coats kills them with chlorine. The dried biomass results in “a semi-crystallized, natural, biological, biodegradable plastic.”

The process, he said, is neither labor-intensive nor overly technical. On a typical dairy, two people could run the operation and monitor dissolved-oxygen levels and temperature.

Coats said there are many uses for biodegradable plastics today.

“We’re talking about single-use plastic that we throw away each day,” he said — planting pots for the nursery industry, plastic bottles, garbage bags and packing materials, for instance.

Hopefully, much of this “biorenewable” plastic won’t ever hit the landfill.

“On garbage day, it can be put in a recycling station — feed it to the bacteria again and make more plastic,” Coats said.

Coats has been using a scale model to study his project at the university’s small research dairy in Moscow. The mobile laboratory — set in a covered cargo trailer — can process 10 gallons of wet manure each day, producing two to five pounds of plastic.

“That’s a pretty decent result,” he said.

“With PHA selling at a premium, significant economic return could be generated from dairy manure...”

Bob Naerebout, executive director of the Idaho Dairymen’s Association, agrees. Naerebout’s group has financially supported Coats’ work for several years.

The research is “really exciting for society as a whole,” he said. “It’s a great use of a natural resource.”

The concept could be used in other industries, Coats said, but he chose the dairy industry “because it’s a large industry in Idaho, and has a waste stream with a lot of carbon that we can capture.”

The concept could also be a solution to the Greek yogurt industry’s acid whey disposal problem that came up recently in Twin Falls County.

Coats is so far encouraged by the project’s results. He expects to move his research to a working dairy — possibly in the Magic Valley — in 2014. The technology could be implemented full scale in a few years.

Depending on the size of the dairy, the tanks would hold up to 2 million gallons of slurry.

“Dairy manure is a great untapped biomass resource in Idaho,” Coats said.


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