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New Mexico State University

New Mexico State University

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New Mexico, Texas team up to tackle common problem: cow manure

New Mexico and Texas are teaming up to study a common problem: how to handle the manure from a growing number of dairy cattle.

A new system developed at New Mexico State University will take cow manure and turn it into useful products such as electricity and compost.

Researchers from New Mexico State University think they have the answer to the problem: use it to generate electricity.

NMSU researchers Zohrab Samani and Adrian Hanson have developed a "digester" system that will take dairy cattle manure and convert it to methane, which can be used to generate electricity. Their digester is specifically designed for areas such as New Mexico and West Texas, where water is scarce and cows are kept in open corrals.

NMSU has recently received a $321,000 grant that will enable the researchers to build a full-scale digester system to test their process. The model digester will be built in La Mesa, N.M., where a local grower will use this electricity to heat greenhouses and will use a byproduct of the process - compost - to help grow plants.

Manure for the digester system will be trucked in from local dairies. New Mexico has the seventh-largest herd of dairy cows in the country, with an estimated 320,000 cows. These cows generate about 2.6 million tons of manure a year. As it breaks down, this manure produces approximately 1.5 million tons of methane, a greenhouse gas associated with global warming.

The high plains area of Texas is one of the fastest-growing areas in the country for dairy cattle, according to Steve Amosson, an economist with the Texas Cooperative Extension Service in Amarillo.

Although the dairy industry is under pressure to reduce the pollution that results from cow manure, there has been little success in this area. One reason is the complexity and cost of existing digester systems. Another reason is that no digesters have been developed for areas where water is scarce.

Samani and Hanson, who work in NMSU's Department of Civil and Geological Engineering, have spent nearly 10 years trying to develop a digester process that is particularly designed for such areas. Their system is easy to build and operate, requires minimal water use and produces high-quality methane in less than a month. In addition to New Mexico and West Texas, it could be used in Arizona, California and Mexico.

Collaborators on the demonstration project include the New Mexico Mineral and Natural Resources Department; the Texas State Energy Conservation Office; and WERC, an NMSU-based consortium for environmental education and technology development. Samani said he hopes to have the digester built in about a year.

The digester will be able to handle approximately 5,000 tons of manure a year and is expected to generate about 1,500 kilowatt-hours of electricity a day. This is enough to provide power for 40-70 homes.

The project will investigate several options, including selling excess electricity to El Paso Electric or excess methane to the city of Las Cruces, N.M., for natural gas. Natural gas is 90-95 percent methane.

Samani said he hopes the demonstration project will prove that digester systems are economically viable. He noted that the digester system has many economic advantages for farmers, including renewable energy tax credits at the federal and state levels.

The new digester system also will help utilities in New Mexico meet the state's goal of producing at least 10 percent of their electricity from renewable resources by 2011.

"Cow manure could produce 20 percent of New Mexico's energy needs," Samani said.

Samani noted that in addition to cow manure, the NMSU process could be applied to municipal waste or other agricultural waste. NMSU researchers recently completed a test of the process using municipal waste from the city of Albuquerque.