by Avery Yale Kamila
Published in SOSUpdate
(SOS Update, April 2002) At Barham Farm, a 4,000 head hog farm near Zebulon, North
Carolina, farmer Julian Barham and
North Carolina State University are turning hog waste into electricity. The process centers on biogas, which is 70
percent methane and 30 percent carbon dioxide.
In order to capture the gas, an anaerobic digester was constructed. This is a closed system that contains
decomposing waste and the resulting biogas. The gas is then used as fuel in an electric generator. A variety
of generators can be used, including internal combustion engines, microturbines and fuel cells. Barham Farms
uses an internal combustion engine.
At Barham Farm, the electricity savings range from $1000-$1500 per month. In the Midwest,
utility companies contract with local farmers to buy electricity generated from biogas.
However, with the current regulatory arrangement in North Carolina, it makes more sense for farmers to use
the electricity on the farm. That is because electric customers pay an average of eight cents per kilowatt
hour for electricity and can only sell it for an average of two cents per kilowatt hour.
As the waste breaks down in the digester, 80-90 percent of the organic matter changes from a solid
state to biogas. The remaining effluent flows out of the digester and into a traditional lagoon.
From there the effluent, which is rich in nitrogen and phosphorous, is pumped into a series of greenhouses
and used to grow hydroponic tomatoes.
The resulting tomatoes have a higher sugar content, and therefore better flavor, than traditional tomatoes.
Mr. Barham is working to receive organic certification for his tomatoes.
"We hope to develop an integrated system that is profitable," said Jay Cheng, Assistant Professor of
Biological and Agricultural Engineering at North Carolina State University and coordinator of the Barham Farm project.
Another benefit is a reduction in methane gas odor. Professor Cheng recalls a visit to Barham Farm by Iowa
Senator Tom Harkin. The Senator remarked that he'd never been to a hog farm that had so little odor. A dairy
farm in Wisconsin had a similar experience. After installing a biogas system, methane gas odor was reduced
by more than 90 percent.
Microturbines
Farmers in Colorado and Japan are using microturbines to generate electricity from biogas. Microturbine emissions
typically contain less that nine parts per million of nitrogen oxide. In comparison, the average coal fired power
plant in North Carolina emits about 354 parts per million of nitrogen oxide.
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