New Biofilter Reduces Odour and Saves Money

US - Anyone who lives in or around farm country has at one time or another wrinkled their nose and said "What's that smell?" Too often, it's the odor coming from a nearby livestock building. At best, these odours can strain the relationship between a livestock producer and his neighbors. At worst, they can lead to legal battles that leave everyone unsatisfied.
calendar icon 2 November 2010
clock icon 5 minute read

Two Extension specialists at the University of Illinois are working on the design of an innovative biofilter that will help reduce those odour emissions from fan-ventilated livestock buildings. Ted Funk, an Extension agricultural engineer with the Department of Agricultural and Biological Engineering (ABE), and Matt Robert, a research engineer with the department, have constructed two biofilters on the ABE research farm that have the ability to reduce odour emissions by up to 90 per cent.

"The new design uses 30-inch concrete silo staves that fit together like puzzle pieces," said Mr Robert. "A hoop around the outside holds the staves together. The flooring is constructed of wood pallets or poultry flooring, and held up by eight-inch concrete blocks. We lay a geotextile fabric over the flooring to keep the biofilter media in place and still allow for adequate airflow. Then the structure is filled with two to three feet of media, in this case, woodchips and compost."

Mr Funk said ductwork for the structure can be made from 10-mil black polyethylene, the heaviest black plastic sheet available. "We'll use a heat gun to weld the polyethylene into a 24-inch diameter tube that will be attached to the fan. A cable will be trapped inside the tubing so it can be suspended from t-posts and protected from wind and weather."

With all the components in place, a ventilation fan will blow air from the livestock facility into the plenum under the floor of the structure. The air then seeps up through the biofilter media and that's when the "magic" of biofiltration occurs.

"When you keep the biofilter media moist, you get a bacterial film growing on the outside of those particles," said Mr Funk. "The gases are adsorbed into that moist biofilm and the bacteria go to work on them. They're degraded into something that has no odour - carbon dioxide and water - so the odour from the facility is reduced between 80 and 90 per cent."

Mr Funk said one of the greatest benefits of the new biofilter is that it can be constructed by livestock producers themselves using materials that are readily available, at a cost that is not prohibitive to their operation.

"Reducing odour and being a good neighbor sound good until it comes to the pocketbook," said Mr Funk. "Biofiltration has been around a long time in other industries, but it's never been brought down to a cost that the livestock industry can handle."

"Instead of starting from scratch, paying for concrete to be poured, buying new flooring, etc.," said Mr Robert, "this design allows producers to build a structure themselves with material they either have around their site or they can buy from the nearest farm supply store."

One of the biofilter structures on the ABE farm is circular and the second is elliptical, a more unconventional shape. The decision to construct a biofilter in an elliptical shape was made with the producer in mind. "There are some farmers who might have to fit this into a narrower footprint, closer to a building," said Mr Funk. "So we asked ourselves, is there any reason it has to be round? It turns out it doesn't."

"We wanted to try the elliptical because it's never been done, and we wanted to see if we could actually use the staves and have them stay in an ellipse once we backfilled dirt against them," said Mr Robert.

Mr Funk said one thing they are still working on is moisture management. "If the biofilter media gets too dry, the bacteria go out of business, and if it gets too wet liquid will go through the system and collect under the structure. Too much moisture also tends to create compaction problems which make ventilation more difficult.

"The moisture level has to stay between 45 to 60 per cent, so we're working on a sensor that can detect that and couple it with an irrigation system to keep it in the right range," he said. "We don't want the producer to have to grab a sample of the biofilter media, squeeze it, guess if it's the right moisture and then turn the water on. We want to make this as automatic as possible, with a control system that is as economical as possible for the producer."

Mr Funk said the life of the biofilter media will probably be anywhere from three to five years, and the cost of materials is approximately a dollar per cubic foot per minute (cfm) of air handled. "That's a Mr Funk concluded. "We think it's really going to catch the interest of livestock producers."

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