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The Smell of Wealth

Sean Henahan

A North Carolina State University scientist has developed a simple method for processing animal waste, which may lead to productive uses for some of the 500 million tons of poultry and livestock waste produced in the United States each year. Dr. Jason Shih, professor of poultry science at N.C. State, has developed a system called thermophilic anaerobic digestion, which converts animal waste into various useful products, including methane gas for fuel, liquid nutrients for aquaculture, and nutrient-rich feed additives for the poultry and livestock industries.

The thermophilic anaerobic digestion process involves enclosing animal waste in containers with heat-loving bacteria. The waste in the digester unit is heated to more than 115 degrees F. Bacteria in the digester then convert the waste into biogas, which can be used as fuel. The bacteria also destroy pathogens in the solid residue that remains. These by-products can then be processed as sanitary, nutrient-rich feed supplements.

"This brings us one step closer to the concept of holistic farming - where waste will no longer exist, and everything will be recycled in a safe and sanitary way," notes Dr. Shih.

Demonstration projects in China and North Carolina indicate that the thermal recyclers are very productive. Based on measurements of the energy output obtained from the two demonstration digesters, Shih estimates that a farm with 50,000 chickens could produce nearly 10 million British thermal units (Btu) of energy a day using thermophilic anaerobic digestion - enough to supply electricity to 200 homes.

The technology used in the thermophilic anaerobic digesters was first developed during the U.S. energy shortage of the early 1970s. However, the earlier systems were less efficient and more complicated to operate than the current system, said Shih. "Since then, we've discovered that when you digest the waste at a higher temperature, you speed the process, which results in a greater rate of methane gas production from a smaller-volume digester."

Feather-Eating Bacteria

In the course of his work, Shih discovered a bacterium, Bacillus licheniformis Strain PWD-1, which thrives on feathers, breaking them down into a feather-lysate compound. Feather-lysate provides a low-cost, highly digestible protein source for livestock feed, he notes. The feather-eating Bacillus has also been shown to secrete a keratinase enzyme that may offer other potential applications. The keratinase enzyme hydrolyzes proteins such as collagen, elastin, and keratin. Therefore, it could be useful in the breakdown of livestock carcasses, according to Shih.

Shih and his colleague, Dr. Eric S. Miller, also of NCSU, have managed to identify the DNA sequence that controls production of the keratinase enzyme. They are now working on cloning the keratinase gene. Successful manipulation of that gene could lead to mass production of keratinase, which might in turn allow wider use of the product, he said.


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