Two Iowa State University agricultural engineers are revisiting an old idea for reducing livestock facility odor emissions, but with a new twist.

The idea of pushing air from building exhaust fans through a biofilter has been around for more than 40 years. Biofilters can be made of many different materials, including compost, straw and wood chips.  

Although biofilters are relatively inexpensive to build, most producers reject them because of the added energy costs because exhaust fans must continuously run through the biofilters, says Steve Hoff, professor of agricultural and biosystems engineering at Iowa State.

"We're trying to do some different things with biofilters to make them as cost effective as possible," he notes. Hoff is working with Jay Harmon, also an agricultural and biosystems engineering professor, on a project funded by the Iowa Pork Producers Association and a USDA grant. The project has been running for 15 months at a commercial swine finishing operation near Stratford, Iowa.

Past research conducted in Minnesota and South Dakota has shown that odors from a livestock production building can be cut by 90 percent when air exhausted from the building moves through a biofilter. The idea Hoff and Harmon are working on is to limit the amount of air treated through a biofilter.

"We don't need to treat the air all the time," says Hoff. "We know odors travel farthest during nighttime, so we filter the exhaust air during summer evening hours, and only if the atmospheric conditions dictate treatment. But if it's a calm, sunny day, we know odors will disperse quickly and we can bypass the biofilter."

The researchers have developed a system to monitor such things as temperature, humidity, wind speed, wind direction and solar energy. This system automatically controls whether a building's exhaust fans run through the biofilter or bypass it.

"We think we have a method that will result in effective odor control, and be cost effective," says Hoff. "I don't hesitate to tell producers this is something they should consider if the need arises."

Hoff adds that biofilters can last for several years, so construction costs can be spread out over many groups of pigs.