Fall 2008

Biofilters Now Eligible EQIP Practice

PRINT VERSION (pdf) Download the Fall 2008 issue of Iowa Manure Matters - Odor and Nutrient Management Newsletter in pdf format.

By Jason Johnson, Iowa USDA-Natural Resources Conservation Service

biofilterIowa livestock producers with confinement operations can now apply to receive financial assistance to install biofilters, odor-reducing structures fit to the outlet of confinement exhaust fans, through the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS).

Through the USDA’s Environmental Quality Incentives Program (EQIP), eligible producers can receive $2.50 per animal unit for three years, with a cap of 1,500 animal units, to install and maintain biofilters. EQIP is a voluntary conservation program through NRCS that promotes environmental quality in agricultural production. EQIP is available to help agricultural producers protect air quality and reduce the need for regulatory programs.

A biofilter is a device or structure containing an organic material that filters out particulates. Active bacteria attached to the organic material breaks down odorous compounds as they pass through the filter. It is a living ecosystem of microorganisms that continually feed on odorous gases.

Jasper County hog producer Kevin Van Manen took proactive measures last fall when he installed open-bed biofilters on two hog confinements, totaling 3,200-head. He says he can tell a big difference in the reduced odor from his confinements, located adjacent to his home.

Van Manen learned about biofilters from Iowa State University (ISU) Professor Jay Harmon, at an ISU meeting on air quality control. From there, he worked with the Colin Johnson, Iowa Pork Industry Center, to design and implement his system. Van Manen admits making mistakes installing his first biofilter, but says he learned a lot.

Research Shows Biofilters Work
According to Steven Hoff, ISU Department of Agricultural and Biosystems Engineering professor, biofilters are very effective in reducing odor when designed correctly. Hoff has researched biofilters at Greg Carlson’s hog farm in Boone County for four years. His research indicates a reduction in odorous gases after emission from a biofilter compared to an unfiltered exhaust fan.

Hoff says the key to an effective biofilter is the right amount of throat opening from the confinement exhaust fan to the biofilter. If airflow is restricted due to the biofilters, it becomes cost-prohibitive to run fans.

Much of Hoff’s research is now focused on limiting the time a biofilter is in use to cut electrical costs. Hoff is looking at “impact-based control” where he tracks weather patterns and monitors potential downwind neighbor events.  By doing so, air is forced through the biofilters only when needed.

Hoff says biofilters will be more cost-prohibitive if used to ventilate all air from a confinement. Hoff is researching a way for air to bypass the biofilter, only filtering when it’s egregious to neighbors, such as hot summer evenings or when winds are blowing toward adjacent homes.

Design, Construction and Maintenance
The most common type of biofilter, and one eligible for financial assistance through EQIP, is an open-bed biofilter. There are a number of ways to design an open-bed biofilter, but it must contain the following fundamental components to be eligible through EQIP:

  • Ventilation - A biofilter needs to be sized to treat airflows during periods when odors are a concern.
  • Media - 10 to 18 inches of woodchips with the proper amount of porosity, moisture holding capacity, nutrient content and a slow decomposition rate. The estimated woodchip life is 5-8 years, but can be less.
  • Sizing - Biofilters can be configured horizontally or vertically. A horizontal biofilter requires more space, but costs less to build. A vertically-designed biofilter requires less ground space, but costs more to build.
  • Fans - Fans must be able to move air through the building and the biofilter. Fan selection is important because it must be able to handle a flow resistance through the building and filter.
  • Moisture Content - Bed media moisture content should be kept between 40-60 percent for optimal treatment. A garden sprinkler or soaker hose and a timer can facilitate watering.
  • Construction - Biofilters have ducts, usually made of plywood, and a plenum to support the woodchips. The plenum is the structure under the bed that allows for air distribution. Ductwork connects the pit and wall ventilation to the biofilter plenum. Plenums can be concrete blocks or wooden structures with a mesh or screen on top to prevent woodchips from falling through.
  • Maintenance - Key practices include maintaining proper moisture levels, weed removal, rodent control, and monitoring media airflow resistance to prevent clogging.

For more information about EQIP opportunities and biofilters, please visit your local NRCS office.

Online resources include:

University of Minnesota
Biofilters for Odor Control

BAEU-18 Biofilter Design Information

South Dakota State University
FS 925-C Biofilters


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