A recently completed study by Wisconsin ag department 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. 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 state 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. Struss emphasized that the study did not attempt to measure emissions for the entire farms.
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.
Based on sampling results, it appears that the odor model used in Wisconsin's livestock operation 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 final report and farm specific data is available on DATCP web site.