A recently completed study by the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) and the Department of Natural Resources has increased the understanding of air emissions and odors on larger-sized livestock farms, and lays the groundwork for future studies in this important area, officials say. 

The multi-year project to study odor and air emissions from Wisconsin dairy and livestock farms was supported by a Conservation Innovation Grant from the USDA Natural Resources Conservation Service (NRCS).

Larger livestock farms volunteered to be part of the study. Five dairy farms and one heifer raising operation were selected. The farms ranged in size from 400 to more than 2,500 head of cattle. Four manure management practices were evaluated: anaerobic manure digesters, an impermeable cover placed over manure lagoons, a permeable manure lagoon cover, and a solids separation and aeration system.

“The project evaluated the air emissions and odor levels from six dairy and livestock operations and then compared the odor levels both before and after the installation of best management practices that were intended to reduce odor or emissions,” said Steve Struss, project co-manager with the Wisconsin agriculture department. 

More than 2,000 air samples were collected during the project. The samples measured odors and the airborne concentrations of ammonia and hydrogen sulfide, two compounds most likely to be present on livestock operations.

“Keep in mind that we were not measuring the amount of emissions from entire farms,” Struss said. “The samples were collected at the edge of practices such as manure lagoons, sand separation channels or an animal feed lot.”  

While the number of farms within the study was limited, it appears that impermeable covers significantly reduce ambient concentrations of ammonia and hydrogen sulfide. Not surprising, when stored manure was agitated or pumped, higher concentrations of ammonia and hydrogen sulfide were detected. The project will also provide some valuable data for the existing livestock facility siting rule.

“The siting rule uses a model to predict the amount of odor that might be produced from new or expanding livestock operations. One goal of this project was to compare the levels that the model predicts with actual odor levels measured on farms,” Struss said. “The study gives us some real world data that we can consider in evaluating the odor model."  

Based on sampling results, it appears that the odor model used in the DATCP siting process accurately predicts the odor from covered manure storage lagoons and the amount of odor from manure lagoons between two and four acres in size. However the model appears to underestimate the amount of odor from small manure lagoons and manure digesters.

The findings of the study suggest options for farmers who wish to reduce odors from their farm, among them:

  • Minimize surface agitation of waste storage lagoons to limit exposure to the air including the use of submerged inlet pipes and mixing below the surface of the lagoon.
  • If a manure digester is used, maximize the time manure is kept inside the digester to reduce odors from the manure lagoon.  A high quality flare with a reliable igniter to burn off gas also avoids unintentional releases of digester gas.
  • Installation of new manure storage lagoons would benefit greatly from an impermeable cover which can reduce odors by 100 percent.
  • Existing manure storage lagoons would benefit from a permeable cover which can reduce odor by about 70 percent.
  • Keep stored feed clean and dry.  Wet feed produces odors and reduces feed quality.
  • A solids separator can be used to produce bedding materials and reduce odor by approximately 25 percent.
  • Keep animal densities low on open feedlots as high stocking rates increase odors as well as runoff and erosion. 
  • Separation distance from neighbors is a simple, but effective tool to reduce odor impacts, place new livestock housing or manure lagoons as far as possible from nearby residents.

“The entire project illustrates what can be accomplished when public agencies work cooperatively toward a common goal. This project was a great effort by staff from our agency and the Department of Natural Resources over a three year period,” said state agriculture secretary Rod Nilsestuen. “We’re grateful to our federal partners at NRCS for their financial support and to the farmers who participated in the study.”

Al Shea, DNR Air and Waste division administrator said, “The strong partnership and excellent work by both our staff and DATCP staff benefitted greatly from the Conservation Innovation Grant. This effort produced a greater understanding of management practices on odors and air emissions on Wisconsin farms.”

“This project is exactly the type of work that Conservation Innovation Grants are for,” said Pat Leavenworth, State Conservationist for the USDA NRCS in Wisconsin. “Testing new technology on the farm, and tackling the big environmental issues like air quality on livestock operations are important topics.”

The final report and farm specific data is available here.

Source: Wisconsin Department of Agriculture, Trade and Consumer Protection