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New Mexico State University

New Mexico State University

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NMSU researchers to field-test technology for converting biomass into energy

New Mexico State University researchers have teamed with Sierra Vista Growers and regional dairy farms to field-test an anaerobic digestion technology to convert cow manure into methane that can be used to generate electricity.

New Mexico's dairy industry is the largest cash-producing agricultural commodity in the state with an economic impact estimated at $2.1 billion annually. However, the industry faces a big challenge in disposing of a high volume of waste in an environmentally and economically sound manner. The estimated 330,000 dairy cows in New Mexico produce almost eight million tons of wet manure waste annually.

Researchers from the NMSU College of Engineering and WERC: A Consortium for Environmental Education and Technology Development are developing a system that uses an anaerobic bio-digester to turn manure into energy and useful byproducts.

The project is supported by the State Technologies Advancement Collective (STAC), through the New Mexico Energy, Minerals, and Natural Resources Department and the Texas Energy Commission.

An anaerobic bio-digester is a mechanical system that decomposes organic matter, in this case manure, to produce methane that can in turn produce electricity and byproducts such as potting media and soil amendments that are better than commercial-grade fertilizer.

WERC Associate Director George Mulholland and civil engineering professors Zohrab Samani and Adrian Hanson are evaluating the pilot-scale system.

"What we're doing [with STAC] is gathering good quantitative data we hope will show that this process will be both an economic plus for the dairy industry and will help to solve the environmental issues associated with disposing of dairy cattle waste," MulHolland said.
Construction of the working device, based on prototype analysis, gets under way in late June.

"The conversion process consists of three solid-phase reactors that will produce methane," said Hanson. "A six-kilowatt generator will be used to produce electric energy and approximately 60,000 British thermal units (BTU) per hour of thermal energy. The electrical output will be enough to sustain up to four dwellings."

Natural gas consists of about 90 percent methane, yielding a BTU/cubic foot value of about 1,000. Biogas is 55 to 65 percent methane, 30 to 35 percent carbon dioxide, with some hydrogen sulfide, nitrogen, and traces of other gases. Its heating value is around 600 BTU per cubic foot.

The potential exists to produce up to 50 megawatts of electrical output. The closed-system technology for treating dairy manure works especially well in arid climates like New Mexico's because it does not require much water.

STAC is a program that allows states, territories, and the federal government to collaborate on energy research, development, demonstration and deployment of energy-related projects.

WERC is one of three units of the newly established Institute for Energy and the Environment (IEE) in the NMSU College of Engineering. The IEE also includes the Southwest Technology Development Institute and the Carlsbad Environmental Monitoring and Research Center.

For more information on IEE environmental technology development projects, contact Abbas Ghassemi, executive director, at (505) 646-2258 or visit www.werc.net.