Winter 2000
Biofilter project smells of success
by Sherry Hoyer, Iowa Pork Industry Center
A demonstration project at the Kirkwood Swine Facility at Kirkwood Community College in Cedar Rapids is pleasing to both smell and sight and that’s just what project organizers had in mind. Iowa State University (ISU) Extension livestock field specialist Terry Steinhart and ISU Extension agricultural engineer Greg Brenneman designed a biofilter for the exhaust system at the college’s 10-stall farrowing house to decrease odors and blend in visually with the surroundings. This Iowa Pork Industry Center-funded project has succeeded on both counts, Steinhart said.
The entire biofilter is roughly the size of a king-size bed.
“Because of its location on campus, this biofilter needs to be nice-looking and not have grass sprouting from it,” he said. “The idea of using a biofilter is to cut down or eliminate the odor, and the smell coming from the biofilter is very similar to that of soil after a rain.”
A biofilter is a device or structure containing biological material that serves as a filter by allowing air to pass through it. A true biofilter has active bacteria growing in the biological material that break down odorous compounds as they pass through the filter. A biofilter is not like a dust filter that fills up and must be cleaned; instead, it is a living ecosystem of microorganisms that continually feed on odorous gases.
Steinhart and Brenneman visited with Richard Nicolai of the University of Minnesota’s Biosystems and Agricultural Engineering Department and used his recommendation when designing this biofilter. The recommendations are available in a document called Biofilter Design Information at http://www.bae.umn.edu/extens/aeu/baeu18.html
Building the biofilter wasn’t a difficult process and the cost was relatively low, too. Steinhart and Brenneman said it took three people working 5 hours to complete the biofilter. This demonstration project is a bit more costly because they chose to build a “box” to contain the biofilter material for its visible on-campus location.
“On a farm design, there wouldn’t necessarily be a need for sides on a producer’s biofilter, so we would get used pallets and cover them with 1/4-inch mesh wire,” Steinhart said. “A plenum would be constructed of plywood to distribute the air under the pallets and up through the compost material. Compost and wood chips should be available at little or no cost.”
In addition to building the biofilter, Brenneman said producers need to remember two things when considering whether to add a biofilter to a facility’s exhaust system. “A good rule of thumb is that you need about 1 square foot of biofilter material for every 10 cubic feet per minute of ventilation,” he said. “And, remember that your exhaust fan will need to operate against a higher static pressure when you’re using a biofilter. This means your fan should be able to provide adequate airflow at least 1/4 inch and preferably up to 1/2 inch of static pressure. Replacing your fan with a more powerful one is where the cost comes in for a producer.” Fan replacement cost is estimated at $350–400.
The Kirkwood biofilter is made from a 2 foot by 8-foot piece of plywood and 2 ´ 6 boards on end that are covered with 1/4-inch mesh wire on the bottom. The building pit air is forced into the space below the mesh and through the biofilter material between the 2 ´ 6 boards. Steinhart said the wire mesh keeps the wood chip and compost material from falling into the area where the exhaust air enters the biofilter. The plenum acts like a chimney to push the conditioned air through the filter material. Current biofilter material includes wood chips, horse manure, sawdust, straw, and cornstalks, although the mixture may vary according to what is available and moisture content.
“One problem is that the material must be kept moist, otherwise the bacteria go dormant and aren’t able to work on the odor coming into the material,” Steinhart said. “However, you also can over water. If the material becomes anaerobic, the lack of oxygen essentially turns the compost back into manure.”
Steinhart said he doesn’t think there will be a problem with the material freezing in the winter, as long as the right moisture balance can be established. He also plans to add small worms (see Petersen article in this issue) to the compost material in the spring to help provide consistency in the aerobic decomposing process.
Both said they are willing to work with other ISU Extension livestock and ag engineering specialists on specific plans for producers, but advise producers to start the process by having the National Pork Producers Council conduct an odor and environmental assessment of their facilities.
“This is a free service and it will help you locate problem odor sources,” Steinhart said. “Where is the odor coming from—pit fans, exhaust fans, lagoon? If it’s from exhaust fans, this system might be a good ‘odor eater’ for your operation.”
For more information on biofilters contact Terry Steinhart, Keokuk County Extension, (515) 622-2680, tsteinha@iastate.edu; Greg Brenneman, Johnson County Extension, (319) 337-2145, gregb@iastate.edu; or me at (515) 294-4496, shoyer@iastate.edu.
