Reprinted, with permission, from the proceedings of: Mitigating Air Emissions From Animal Feeding Operations Conference.
A biofilter is simply a porous layer of organic material, typically wood chips or a mixture of compost and wood chips, that supports a population of microbes. Odorous building exhaust air is forced through this material and is converted by the microbes to carbon dioxide and water. The compounds in the air are transferred to a wet biofilm that grows on the filter material where microorganisms breakdown the odorous compounds.
Biofiltration can reduce odor and hydrogen sulfide (H2S) emissions by as much as 95% and ammonia by 65%. The method has been used in industry for many years and was recently adapted for use in livestock and poultry systems. Biofilters work in mechanically ventilated buildings or on the pit fans of naturally ventilated buildings. Biofilters can also treat air vented from covered manure storage.
Two configurations of biofilters are being used to treat exhaust air from swine buildings: a horizontal media bed and a vertical media bed. Horizontal biofilters require more land area but are less expensive than vertical biofilters. Horizontal beds can be shallow (< 0.45 m) or deep (> 0.75 m).
Key factors influencing biofilter size and performance:
Costs to install a biofilter include the cost of the materials—fans, media, ductwork, plenum—and labor. Typically, cost for new horizontal biofilter on mechanically ventilated buildings will be between $150 and $250 per 1,700 m3/hr (1,000 cfm). A vertical biofilter is approximately 1.5 times the cost of a horizontal biofilter. Annual operation/maintenance of the biofilter is estimated to be $5-$10 per 1,700 m3/hr (1,000 cfm). This includes the increase in electrical costs to push the air through the biofilter and the cost of replacing the media after 5 years.
R.E. Nicolai1, K.J. Janni2, D.R. Schmidt21South Dakota State University, 2University of Minnesota
Point of Contact:
Richard Nicolai, firstname.lastname@example.org
The information provided here was developed for the conference Mitigating Air Emissions From Animal Feeding Operations Conference held in May 2008. To obtain updates, readers are encouraged to contact the author.