|Lagoon covers do an excellent job of reducing manure odors and air emissions such as ammonia and hydrogen sulfide, a Wisconsin study found.
A three-year, $1.6 million project on six Wisconsin dairy operations is shedding light on management practices that control odors and emissions—and those that don't.
The project evaluated air emission and odor levels of five freestall dairy operations and one open-lot heifer-raising facility, ranging from 400 to more than 2,500 head.
"We evaluated levels both before and after the installation of best management practices that were intended to reduce odor or emissions,” says project co-manager Steve Struss of the Wisconsin Department of Agriculture, Trade and Consumer Protection.
The project, completed this past fall, was jointly conducted with the Wisconsin Department of Natural Resources. Dairy producers, industry officials and university engineers served as technical team members.
More than 2,000 air samples were collected from the six farms. The samples were measured for odor and for concentration of hydrogen sulfide and ammonia.
"Keep in mind that we were not measuring the amount of emissions from entire farms,” Struss says. "The samples were collected at the edge of practices, such as manure lagoons, sand separation channels or an animal feed lot.”
The abatement practices included anaerobic manure digesters, an impermeable lagoon cover, a geotextile permeable lagoon cover and a solids separation and aeration system. The results were as follows:
- The impermeable cover reduced odors and ammonia emissions by 100%.
- The geotextile cover was 70% effective. "The permeable cover is one-third the cost of the impermeable, yet it gave quite a bit of odor and emissions control,” Struss says. "It gave the best bang for the buck.”
- Anaerobic digesters had mixed results. One reduced odors by about 15% while another actually increased odors by 15%. Both digesters reduced hydrogen sulfide levels, but ammonia levels were elevated. "The digesters didn't provide much control,” Struss says. Longer retention times of the manure in the systems would probably result in lower emissions, but the systems would have to be redesigned, he says.
- The combination of solids separation and aeration reduced odors by 25%. But concentrations of hydrogen sulfide and ammonia were increased.
The study results were also used to evaluate the odor model that the Wisconsin Department of Agriculture employs when siting dairies. "The study gives us some real world data that we can consider in assessing the model,” Struss says.
Based on sampling results, the model accurately predicts odor from covered manure storage lagoons and large, two- to four-acre uncovered lagoons. However, the model underestimated the amount of odor that is produced by small, uncovered lagoons and manure digesters.
The study also confirmed that separation distance from neighbors is a simple but effective tool for reducing odor effects. The farther from neighbors, obviously, the better.
More on the project; case studies