A PIECE of plastic made by Erik Coats' research team doesn't look particularly special; it's clear and flexible like a piece of sandwich bag.
However, unlike the usual petroleum-based plastics, this is made from cow manure.
Coats is an associate professor of civil engineering at the University of Idaho. His research team has developed a unique system to transform manure into polyhydroxyalkanoate (PHA), a biodegradable plastic.
"We are the only research group looking to advance this technology in the U.S.," Coats said.
The project is part of Coats' overall goal to find valuable uses for municipal and agricultural waste streams — like the 250 million tons of manure dairy cows produce every year in the U.S.
"It's all about developing better technologies that really move us forward in society in our use of organic waste," he said.
A pilot-scale model of the manure-to-plastic system is now operating at the University of Idaho dairy. It can turn 10-12 gal. of wet manure into up to 5 lb. of plastic each day.
The system begins by fermenting the carbohydrate-rich manure to produce organic acids, including acetic acid, which become food for a tank full of naturally occurring soil bacteria that Coats' team harvests from the local wastewater treatment plant.
The bacteria store excess organic acids as PHA. When the bacteria are killed and dried, the researchers can separate out the PHA as a crumbly, white, raw plastic.
With processing, PHA can be used in myriad products. Coats envisions applying it to single-use materials like packaging as well as products for which biodegradability comes in handy, like planter pots or erosion-control mats.
PHA is currently produced on a small scale elsewhere, but it's mostly made from corn sugar — meaning corn is diverted from the human and livestock food supply — and the process requires pure bacterial cultures, creating a large carbon and energy footprint.
Coats' system, on the other hand, leaves a relatively small carbon footprint, uses natural materials and relies on a resource farmers are happy to be rid of, the university explained.
The manure-to-plastic system also can dovetail with anaerobic digesters, which convert manure to electricity and are rising in popularity. Fermented manure can be split into solids and liquids, with the liquids used for plastic production and the solids used for electricity, Coats said.
After the team collects data from the pilot system at the university dairy, they plan to move the system to a dairy complex in southern Idaho and install it alongside a digester.
Coats' system could apply to waste streams beyond dairy manure, as well. His team is studying ways to make plastic from the manure of other animals, waste from tomato canneries and municipal wastewater.