Monitoring methane

Agricultural Research, June, 1995 by Don Comis

Harper explains that lagoons are large, shallow pits, from 0.25 to 5 hectares in size, where all water used in dairy or swine barns is stored. They look like lakes, except for the color of some of them and for the continuous methane bubbling. "Sometimes, huge bubbles bring large mats of organic matter from the bottom mud up to the surface," Harper says.

Most of the wastewater comes from hosing down the barns to flush out manure. As an environmental measure, farmers store the liquid manure in the lagoon and apply the wastewater to their farmland as needed for fertilizer.

Harper and his colleagues mounted the equipment on a metal barge 2 meters wide by 6 meters long, and floated the barge on pontoons out to the middle of the lagoon. They let legs attached to the barge sink down for support. Then they let air out of the pontoons until the barge sank a couple of inches below the water's surface, thus keeping the barge's frame from interfering with the wind.

Monitoring devices project from 20 centimeters to 270 centimeters above the surface of the water. These instruments collect gases from the air and pump them through tubes back to a trailer on the lagoon's banks. There the gases are sampled and analyzed by one of the two laser spectrometers used by Lowry and Sharpe.

Lowry hopes the devices on the barge will not only help modelers better evaluate the gases emitted from animal waste lagoons, but also establish whether there's enough methane emitted to make it worthwhile for a farmer to use the methane as fuel for an electrical generator.

Lowry A. Harper and Ronald R. Sharpe are at the USDA-ARS Southern Piedmont Conservation Research Laboratory, P.O. Box 555, Watkinsville, GA 30677; phone (706) 769-5631, fax (706) 769-8962.