Friday, January 01, 2010

Dairy emission, odor study out

- Larger livestock farms volunteered to be part of the study.

- Ammonia and hydrogen sulfide levels were measured.

- Project provides data for siting rule.

A RECENTLY completed study by the Wisconsin Department of Agriculture, Trade & 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 said.

The multiyear project to study odor and air emissions from Wisconsin dairy and livestock farms was supported by a Conservation Innovation Grant from the U.S. Department of Agriculture's Natural Resources Conservation Service.

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, DATCP project co-manager.

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 feedlot."

While the number of farms within the study was limited, it appears that impermeable covers significantly reduce ambient concentrations of ammonia and hydrogen sulfide, DATCP said. Not surprisingly, the department noted that when stored manure was agitated or pumped, higher concentrations of ammonia and hydrogen sulfide were detected.

The project also will provide valuable data for Wisconsin's 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 we can consider in evaluating the odor model."

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

The findings of the study suggest options for farmers who wish to reduce odors, including:

* 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 from an impermeable cover, which can reduce odors 100%.

* Existing manure storage lagoons would benefit from a permeable cover that can reduce odors about 70%.

* 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 odors approximately 25%.

* Keep animal densities low on open feedlots as high stocking rates increase odors as well as runoff and erosion.

* The 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 are available on the DATCP web site at

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