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Livestock air emission, odor study completed


December 30, 2009
By Marg Land

NEWS HIGHLIGHT

Livestock air emission, odor study completed
A recently completed study by Wisconsin’s Department of
Agriculture, Trade and Consumer Protection and 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.



December 30, 2009,
Madison, WI – A recently completed study by Wisconsin’s Department of
Agriculture, Trade and Consumer Protection
and 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)
.

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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.

“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 final report and farm
specific data is available on DATCP web site by clicking here.


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