Manure transformed into biodegradable plastic

Petro-chemical replacement | Some PHA products are made from corn but using manure is more environmentally beneficial

GUELPH, Ont. — The idea of drinking out of a plastic cup made from cow manure may not seem overly appetizing to some people.

“It’s not particularly appetizing to me either,” said Erik Coats, a University of Idaho civil engineering professor who is researching the chemistry of converting bio-waste into biodegradable plastic.

“The yuck factor is pretty strong.”

Coats’s 24-foot sanitary-white trailer, which serves as an experimental mobile plastic factory, converts 10 U.S. gallons of dairy slurry into five pounds of biodegradable plastic a day.

The trailer is located next to the university’s dairy barns and connected to them by a big hose. It is the only such research project in the United States.

The trailer’s 200 U.S. gallon fermentation tanks are the vital link between the laboratory test tubes of a couple years ago and the first million gallon tank needed for a full-scale commercial production, maybe a couple years into the future.

Coats’s bioplastic carries the scientific title polyhydroxyalkanoate but is more commonly referred to as PHA.

The material is as clear, flexible, scentless and tasteless as a plastic bread bag. There’s not the slightest hint it’s derived from cow manure.

However, to avoid unwanted marketing problems, Coats said his bioplastic won’t be used in food packaging.

“It’s strictly for single use applications like packaging or where a plastic cover must be biodegradable,” he said.

“I met recently with some folks who treat seeds with nutrients and fungicides wrapped in a polymer coating. Our PHA is biodegradable so it’s perfect for something like that.”

In the agricultural sector, a biodegradable plastic might be suitable as bale wrap, baling twine, bags and liquid containers.

Nearly all plastic products are produced from petro-chemicals. Replacing them globally with PHA would go a long way toward relieving pressure on reserves of fossil fuels.

Some PHA products are made from corn, but the downside is that they keep corn out of the human and livestock food supply. Replacing those PHA items with manure-based PHA would be a positive move.

The U.S. dairy herd produces 250 million tons of manure a year, and Coats’s trailer is already producing a reliably predictable product. However, he must now fine tune the chemistry to commercialize the process for a million gallon tank.

He thinks a commercial sized poop-to-plastic plant has a good fit on dairy farms that are already installing bio-digesters. He said the plastics factory would insert between the mixing tank output and the bio-digester tank input.

“Our process does not compromise the operation of bio-digesters, nor do we use a separator,” Coats said.

“The thickened solid slurry that comes out of our fermenter is readily digestible. We simply insert our plastic making equipment in line before the bio-digester tanks.”

He said the process adds pure slurry to a simple fermentor for a short time. Effluent coming out of the fermenter consists of slurry water and solids. Solids go back into the main pipe to the bio-digester, while liquids, which are rich in the organic acids needed to produce PHA, take a different path.

“We feed the liquid to our naturally occurring bacteria. The bacteria convert the acids and store them as a carbon reserve within their cells. This carbon reserve is a polyester-like polymer.”

The bacteria are killed with chlorine to harvest that polymer. At this point, what remains is a true plastic. It looks like crumbly, white particles similar to Styrofoam. The particles are now ready to be manipulated into a commercial product, such as the flexible clear plastic.

“This process can work with any organic waste material: hog slurry, food processing waste, other kinds of livestock manure or municipal waste.”

He said municipal waste is the most difficult to deal with because it can contain many different elements. Chemists don’t know what they’re dealing with from day to day, so it’s hard to tune the system.

“We started with dairy manure because it’s uniform and has the highest concentration of carbon and electrons. It’s the easiest to work with. It’s the best starting point, that’s all. Once we have a full-scale dairy project up and running, we’ll deal with other bio-waste sources.”

For more information, contact the U of I science office at 208-885-7725 or email [email protected]


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