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Students with dairy manure PHA reactors

Research Turns Cow Manure to Biodegradable Plastic

By Erik Coats — Special to Business Insider
Published: November 27, 2012 by the Idaho Statesman

In the search for sustainable energy sources, much attention has been focused on solar and wind power. However, in the quest for a “silver bullet” renewable-energy solution, an often-overlooked option is biomass.

Biomass as an energy source is any type of biological material directly or indirectly used for the production of energy. Common examples range from burning firewood to heat our homes to converting corn to ethanol to fuel our cars.

Student working with the Anaerobic DigesterThere is another excellent biomass source that does not force us to choose between energy and food: dairy manure. Through a process called anaerobic digestion, bacteria can convert manure to a methane-rich biogas, which can be burned in an engine generator to produce electricity.

Dairy manure is a great untapped biomass resource in Idaho. According to the United Dairymen of Idaho, there are 550,000 milking cows in Idaho. Each animal excretes 100 to 150 pounds of wet manure daily. If all that manure were converted to biogas, we could power more than 10 percent of Idaho households.

Just as important are the environmental and economic benefits to Idaho dairies, such as using waste in a beneficial manner to generate revenue. Between dealing with increasing feed and fuel costs and producing a perishable product, dairy operating margins are slim.

Anaerobic DigesterSo how has the manure-to-energy industry progressed? Currently, six dairy anaerobic digesters are operating in Idaho, processing manure from 51,000 dairy cows to generate electricity. Considering the much larger Idaho dairy-cow population, it is reasonable to ask why there are so few digesters processing manure from only 10 percent of Idaho’s dairy cows. The greatest challenge to broad-scale digester deployment is the low cost of electricity in the region. At current wholesale rates, it is difficult to construct and operate a profitable dairy-manure anaerobic digester.

Students with dairy manure PHA reactorsRecognizing the need to help economically stabilize Idaho’s dairy manure-to-electricity industry, my research group at the University of Idaho is developing a technology to produce a second commodity from manure. We are converting it to 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 known as polyhydroxyalkanoate, or PHA. PHA is similar to conventional petroleum-based plastics, including polyethylene and polypropylene. But in contrast to these petro-plastics, PHA is biodegradable and can be biologically produced from otherwise unwanted organic waste.

As one might imagine, there are a number of uses for a biodegradable, biorenewable plastic, such as single-use packaging materials, planting pots for the nursery industry and plastic bottles. Moreover, with PHA selling at a premium, significant economic return could be generated from dairy manure beyond electricity.

We are constructing a mobile pilot-scale system and will begin testing at full-scale dairies in 2013. Pending success of these trials, we are optimistic that the technology can be deployed at full-scale dairies in three to five years.

Our progress to date on this biomass energy technology could not have been realized without the critical support of the Idaho Dairymen’s Association, the Idaho National Lab (through a grant provided to the Center for Advanced Energy Studies), the National Science Foundation and the Idaho State Board of Education’s Higher Education Research Council. We look forward to working with these entities and others throughout the state to help expand the use of biomass for energy.

Erik Coats, University of Idaho associate professor of civil engineering. ecoats@uidaho.edu