Julian Barham treats the waste produced by his 4,000 sows using an in-ground digester that produces bio-gas that fuels a generator, which produces electricity for the farm.

The system has been in place since 1996 and is one of five waste management technologies identified by scientists at North Carolina State University (NCSU) as promising alternatives to lagoons and spray fields.

NCSU scientists plan to evaluate all five technologies on a full-scale basis – including demonstrations on operating hog farms. They may expand to as many as 11 potential full-scale tests of the technologies.

Digester Converts Waste into Power, Reduces Odor

Dr. Jay Cheng, assistant professor at the NCSU Department of Biological and Agricultural Engineering, has been evaluating the digester on Barham’s farm since 1998. While his evaluation is not complete, Cheng says the technology appears to be a viable alternative.

The digester is 265 x 265 ft. and 20-ft. deep, which is twice the depth of a typical North Carolina lagoon. A tough plastic cover stretches over the digester. As waste decomposes in the digester, bio-gas is created. The gas is piped to a generator that uses it as fuel. The generator produces electric power, which Barham uses on the farm.

Barham runs the generator for most of the day, during which power rates are higher, and turns it off at night. Cost savings for electricity amount to $1,500/month.

The generator also is used to heat water, which is then used to heat barns and keep baby pigs warm.

Cheng points out that the cover over the primary waste treatment area appears to decrease odor. The cover also decreases the release of greenhouse gases. The project, including Cheng’s evaluation, is funded by the AgStar Program, an Environmental Protection Agency program to reduce greenhouse gases.

The excess liquid (containing half of the nitrogen and phosphorus content of typical lagoons) from the digester flows into a lagoon. Barham uses 20% the liquid to irrigate tomatoes in a 28,000-sq. ft. greenhouse. The remainder is sprayed onto nearby spray fields.

Wetlands Used to Treat Hog Manure

Another promising alternative is a full-scale, on-farm constructed wetland being used as a waste treatment system for an Onslow County, NC, swine farm.

Researchers from the NCSU College of Agriculture and Life Sciences are evaluating the wetland’s performance. The wetland was constructed this year and began operating in December.

Wetlands may be an alternative to lagoons and spray fields now used to treat hog manure in North Carolina.

The wetland is used to treat manure from 3,520 finishing hogs in four barns. Waste moves first through a solids separator, where solids are removed and used in a vermiculture operation. Worms are allowed to feed on the waste, decomposing it and turning it into a nutrient-rich soil amendment.

The remaining liquid manure flows into the 13-acre wetland and then into a irrigation pond. While the liquid in the pond is not clean enough to discharge into surface waters, researchers expect it to be much cleaner than typical lagoon water.

For more information, contact Leonard Bull at NCSU by calling (919) 513-6836 or e-mailing leonard_bull@ncsu.edu.