June 3, 1997

NC State Engineers Develop Systems To Reduce Swine Odors

Mention hog farms and what immediately comes to mind are the odors from lagoons and production houses. Recently, swine odors have caused quite a stink among hog farmers and their neighbors -- so much so that they have been the subject of a governor's blue ribbon commission study. Now, thanks to NC State University engineering professors and a taste and smell expert at Duke University, help is on the way to find a solution to the problem of odors in pork production.

The team of researchers is developing a biofiltration system to help farmers monitor and control the odors produced by hog farm operations. Dr. Robert Bottcher, professor of biological and agricultural engineering, Dr. John Classen, assistant professor of biological and agricultural engineering, Dr. Troy Nagle, professor of electrical and computer engineering, and Dr. Philip Westerman, professor of biological and agricultural engineering, are working on the project with Dr. Susan Schiffman, director of the Duke University Medical Center Taste and Smell Research Laboratory.

In a joint program with researchers at Iowa State University and Michigan State University, Bottcher, Classen and Westerman are designing a biofiltration system that will filter odor emissions from hog production houses. As part of the research project, Nagle and Ricardo Gutierrez, an NC State doctoral student in electrical and computer engineering, are developing an electronic swine odor "sniffer machine," or "electronic nose," that will monitor the effectiveness of the biofiltration system. In her taste and smell laboratory, Schiffman uses a panel of human noses to characterize the perception of hog odor emissions. Schiffman's results will be used to calibrate the electronic nose sensors. When completed, the filtration system will offer farmers a tool for reducing swine odors and, possibly, complaints from neighbors.

The filtration system works by forcing the odorous air from hog containment facilities through biofilters packed with compost and peat. The odor molecules are adsorbed onto the particles of the biofilter, and naturally occurring bacteria metabolize the odor compounds.

"Peat and compost make good filtration material," said Classen. "The two compounds are readily available and not easily compacted, allowing the air to flow through the filter with less resistance. What we want to create is an efficient filtration system that is also economical to use. Filters made of common materials such as peat and compost meet these requirements."

The electronic nose being designed by Nagle and Gutierrez will offer farmers and others a device that can measure the intensity of the odors. The scientists believe that the new system, coupled with modifications in swine production methods, can reduce odors to acceptable levels.

Nagle's sniffer machine is in bench-top testing stages. When completed, the electronic nose will be able not only to identify and measure swine-related odors but also to monitor the efficiency of the filtration system.

"Our initial goal is to design a simple metal oxide device with just a few sensors that we could build for the biofiltration project," said Nagle. "We can also create a prototype hand-held device that could be used by farmers and others to monitor odors around swine production operations. So our secondary goal is to create a device that is low cost, accurate and portable for field testing at the farms. The hog farmers want to be able to measure the odors, to quantify them, so that they can better control them either with filtration systems or changes in their production methods."

Although the instrument is not as versatile or talented as a human nose, it can measure odors scientifically. The human nose, when exposed to the same aroma over time, becomes accustomed to that aroma and loses its ability to sense it. The electronic nose, however, is calibrated to recognize an odor and is always able to sense it. The device also measures and quantifies odors--a necessary component of regulation and control.

Currently, the sniffer machine is a bulky contraption in Nagle's biomedical instrumentation laboratory that Nagle and his students use to experiment with different sensors and their responses to odors. The sensors are calibrated to respond to a specific stimulus, and computer software is used to track the sensors' responses to the odor.

In his laboratory, Nagle can create electronic noses for many different industrial and agricultural applications. "We can build a device that can detect many different volatile chemicals or odors," said Nagle. "But for this project, we are focusing on hog odors."

Both professors stress that, with proper management techniques, odors from hog farms can be reduced to acceptable levels. "The treatment of odors is only one option," said Classen. "The primary goal is to eliminate the odors at the source. Since that is not a viable option right now, we have had to come up with ways to measure and reduce the odorous emissions. The biofiltration system we are working on at NC State will give farmers another way to address the problem of odors."

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