Penn State Researchers Use Constructed Wetlands To Reduce Odors From Pig Manure Wastewater

May 19, 2000

UNIVERSITY PARK, Pa. -- The feces, urine and wastewater that are byproducts of hog farms smell to high heaven. To reduce the odors, two researchers in Penn State's College of Agricultural Sciences have found that low-tech, constructed wetlands work well to clear the air.

Field trials in small-scale constructed wetlands in a greenhouse showed an 80 percent reduction in offensive odor compounds from unadulterated swine facility wastewater, says Eileen Wheeler, assistant professor of agricultural engineering. Wheeler and doctoral researcher Susan Wood sought to confirm anecdotal evidence that water treatment in a constructed wetland can reduce odors.

"Swine and other livestock producers in southern states have used constructed wetlands to treat animal waste, and researchers had noticed that smells were not as strong," Wheeler explains. "We wanted to see if we could quantify a reduction in odor in trials that would reflect real-world practices."

Wood, of Batavia, N.Y., constructed eight experimental wetlands in 100-gallon livestock tanks. She filled the tanks with gravel, added a layer of peat moss and planted a commercial wetlands seed mix containing a wide variety of plants, including fescue, redtop and wild rye. She also tested unplanted wetlands containing just gravel.

"Some of the grasses died where the water entered the wetlands," Wood says. "But in general, the planted wetlands effectively reduced odors."

Wood organized eight volunteers in a sensory odor panel that compared air samples from untreated swine wastewater and water that had been treated in the wetlands. The panel rated air samples on an odor scale of 0 to 5, with 5 being the most offensive. "Most of the untreated samples were rated as a 4, and the samples from wetland treatment had an average rating of 1," she explains. "The water that had been through the wetland had a stagnant, earthy smell, but it wasn't offensive."

Wheeler says Wood's research is focused on finding an alternative to other methods of treating swine waste for odor reduction. Current swine waste treatment practices include:

--Mechanical aeration of manure lagoons. Oxygen is bubbled into the wastewater, preventing anaerobic conditions that produce smells. "However, this technology has large power requirements that results in high energy costs," Wheeler says.

--Anaerobic digestion of wastes into biogas. This method requires expensive investment in equipment and high maintenance costs.

--Chemical or biological additives that counteract smells. Research has indicated that the effectiveness of most additives has been questionable.

The next step in Wheeler's research is to construct a large wetlands treatment facility on a local hog operation. If the larger wetland continues to effectively reduce odors, the researchers then will focus on whether it is economically feasible to use treatment wetlands on commercial farms.

The researchers also want to test how the wetlands function under different temperature conditions. "The constructed treatment wetlands that have been built in the South have warmer weather year-round," Wood explains. "We would like to see how these wetlands function during a Pennsylvania winter, or whether some kind of protective structure is required to keep them working."

Wheeler says swine operations can use the treated water as wash water for hosing out hog pens, or they may be able to store the water for use as fertilizer for crops.

"Treated wetlands are a low-tech solution to a major problem for modern hog farms," Wheeler says. "These wetlands have no pumps to fix, and aside from some pipes, very little equipment. It's like having a pet -- you have to feed it, but it can take care of itself most days."

###

EDITORS: For more information contact:

Eileen Wheeler phone: (814) 865-3552.

John Wall: phone: (814) 863-2719 e-mail: