Hogwash? More power, less pollution with pig waste

The faint logo of a rodeo clown graces a utility trailer that sits on Tom Butler’s hog farm in Harnett County, N.C.

The trailer is an unlikely laboratory where Mike Aitken conducts research to reduce water and air pollution from hog waste, a big issue in North Carolina, the second largest pork-producing state behind Iowa.

Aitken and his team in the UNC Gillings School of Global Public Health’s environmental sciences and engineering department purchased the trailer second-hand from a former rodeo clown. Aitken’s collaborator, Glenn Walters, saw the trailer on Craigslist and rushed to see it. “The size, configuration and condition were perfect for our project so I bought it on the spot,” Walters says. “The trailer ended up costing us less than 30 percent of what a new trailer would cost.”

Officially, it’s known as a Gillings Innovation Lab, a collection of projects aiming to solve public health challenges facing North Carolina and the world – but most folks call the trailer the FarmLab.

Parked by a hog-waste lagoon at Butler’s farm near Lillington, the lab is testing Aitken’s idea for removing ammonia from the waste. Ammonia is a desirable fertilizer, but too much can lead to contamination of groundwater and surface water. “There is more nitrogen produced from hog waste in eastern North Carolina than could ever be used for crops in that region,” Aitken says.

What’s more, when farmers spray ammonia-rich waste on crops as fertilizer — a common practice —it generates a smelly hog-waste odor. Ammonia also forms fine particles in the air that cause respiratory problems such as asthma.

So Aitken’s team is removing the ammonia, converting it to nitrate, and then to nitrogen, a harmless gas that makes up about 79 percent of the air humans breathe.

Another project at the site captures methane – a potent greenhouse gas – from the treated hog waste. the methane can be burned and, if connected to a generator, can generate electricity. Investor-owned power utilities buy the electricity through a pilot program the state began in 2007. Farmers generating power receive up to 18 cents per kilowatt hour, much more than utilities typically pay other producers, Aitken says. The payments could significantly help offset the cost to farmers of installing such technology.

Aitken began testing the ammonia removal system in mid-2010. Assisting him are associate professor Steve Whalen, graduate students Sarah Bunk and Eric Staunton, as well as Joe Rudek, a hog-waste policy expert with the Environmental Defense Fund in Raleigh, N.C., who holds master’s and doctoral degrees from UNC’s environmental sciences and engineering department.

Adapted from an article in Carolina Public Health magazine (spring 2010).