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Waste not: Transforming manure

Tamara Scully Published on 31 December 2013
Erik Coats, Nick Guho

Pure bacterial cultures fed a synthetic sugar substrate made from processed corn can make polyhydroxyalkanoate, or PHA, a biodegradable plastic.

But Erik Coats, associate professor of civil engineering, and his team of graduate student researchers at the University of Idaho have designed a system which creates PHA from a naturally occurring, organic waste substrate, utilizing commonly found mixed bacterial populations. It is believed to be the first system of its kind in the U.S.



Coats’ team turns manure into 100 percent biodegradable plastic. The system takes what is already a waste management issue – lots of dairy manure – and creates a product that is environmentally friendly and can potentially replace some not-so-friendly petroleum-based plastics.

This manure-to-plastics system could quickly become big news for dairy farmers.

“The goal here is to advance a technology that will convert the manure into an economically valuable product and in doing so remove the manure from management practices that might be less favorable to the environment,” Coats says. “There is tremendous value to dairy manure.”

Erik Coats with raw PHA plastic samples

Utilizing manure as fertilizer, converting it into compost or perhaps utilizing an anaerobic digester to generate energy are other common ways to gain benefit and reduce the environmental impact of dairy farming.


Coats’ system not only adds a new tool to manure management, it can be used in conjunction with existing manure management practices, potentially enhancing their viability and reducing their environmental impact.

Profiting from waste

By converting manure into usable, 100 percent biodegradable consumer products, the environmental impact of animal agriculture is decreased, the use of petroleum in plastics manufacturing can be reduced, and dairymen can economically profit from what is now primarily a waste product and a handling concern.

“We are considering product opportunities that would generate the highest economic return. These applications will likely be in areas that value its ‘green-ness’,” Coats says of the PHA.

Such products might include planter pots for the nursery trade, coatings for seeds, weed barrier products and erosion-control matting. Coats and his team have not yet done an economic analysis to determine the products that might offer the best returns.

PHA would fetch a premium over other plastics due to its minimal environmental footprint, both in its use of raw materials and in the characteristics of the PHA plastic. PHA is very biodegradable in wet environments. In water, with bacteria, PHA degrades within a few months. But in a dry environment, it won’t readily degrade.

Single-use plastics would be “the ideal opportunity for this plastic,” Coats says. “Even in landfills, it is less of a hazard to the environment than other plastics.”


Enhancing anaerobic digesters

Anaerobic digesters have offered farmers the opportunity to utilize manure to generate energy. But the economics of anaerobic digesters, Coats says, “are tenuous at best.” With a little help from PHA, anaerobic digesters may just be able to realize their potential.

“Our technology readily integrates into anaerobic digesters. We have two peer-reviewed publications demonstrating such,” Coats says. “By integrating the technologies, the product portfolio is improved, the economics are improved, and more value is recovered from the manure.

We are conducting research on an integrated suite of technologies – PHA production, anaerobic digesters for biogas electricity and algal growth on the effluent nutrients,” he explains.

Taking manure and converting it into both PHA and biogas for electricity production is highly feasible. The two processes complement each other, with one utilizing manure solids and one the liquids.

While the initial fermentation process used in making PHA is not needed for anaerobic digesters, adding this fermentation step does not detract from the anaerobic digestion process.

Manure solids are utilized in biogas production. Because the solids are not required for PHA production, a combined system utilizes both components of manure for beneficial purposes.

Making plastic

This manure-to-plastics system begins with fermenting manure in a tank. During this short-retention fermentation process, some of the manure is converted into organic acids. The manure separates into liquid and solid portions.

The manure liquid, which contains the organic acids, is removed from the tank and fed to naturally occurring bacteria, present in any wastewater source. There are 300 known bacteria species that can convert carbon to PHA.

The bacteria feed on the organic acids and store excess carbon, in the form of PHA, inside their cells. They are fed rapidly to build up storage reserves.

The bacteria are then killed via chlorine treatment and dried, and the PHA is extracted. PHA granules are raw plastic. PHA granules “have the same material properties and characteristics as thermoplastics,” Coats says.

Moving forward

“A part of our motivation is to help the dairy industry,” Coats says. “It’s one thing to try to get bacteria to store carbon as PHA, but to do so in an economically viable manner – that is more difficult.”

But Coats is confident his team is well on their way to doing just that. Their prototype system was developed using small fermenting tanks, processing a mere dozen gallons of manure per day. This small-scale model results in a bit more than 2 pounds of PHA production daily.

“We completed three months of pilot testing this fall, which provided critical feedback on process operations that we are now studying in the lab. The pilot unit will be in operation again next spring,” Coats says. “We are optimistic that commercialization can occur within two to five years with options for small and large farms,” he adds.

Coats says he believes scaling up can happen with relative ease. It will be a practical system, cost-effective for farmers, beneficial to the environment and compatible with other manure-handling technologies, such as anaerobic digesters.

“It is sequestering carbon. It is providing an environmentally benign product, using nothing genetically modified. It is a productive use of waste. It recovers resource value and is a way to better manage these concentrated waste streams,” Coats says.

“Our goal is to have a platform that maximizes capture of the manure resource to produce maximum economic value while concurrently improving environmental conditions.” PD

Tamara Scully, a freelance writer based in northwestern New Jersey, specializes in agricultural and food systems topics.

PHOTOS 1:Erik Coats, left, with Ph.D. student Nick Guho, with the manure-to-plastics system they’ve developed – along with a team of graduate students – at the University of Idaho.

PHOTOS 2:Professor Erik Coats with samples of the raw PHA plastic and the processed biodegradable plastic generated through the innovative manure-to-plastics fermentation system being developed at the University of Idaho. Photos courtesy of University of Idaho.