As the U.S. urban population continues encroaching on previously rural areas, neighbor complaints about odors emanating from hog operations are a growing concern. Lawsuits against pork producers claiming loss of quality of life have surfaced and continue to be a nagging risk. What’s more, legislative and regulatory actions may get more stringent and require greater investments from pork producers to remain in compliance.

Current acceptable air-emission limits are regulated by the Clean Air Act of 1990. In 2006, the Environmental Protection Agency organized the National Air Emissions Monitoring Study, or NAEMS, to accurately assess emissions from livestock, dairy and poultry production operations. Researchers at Purdue University oversee the pork segment of that effort.

The study has been completed and EPA is currently reviewing the data; however, it may be months before findings or recommendations are made public. “EPA does not plan to make a decision within 15 months of the final report submission,” says Teng Teeh Lim, assistant professor, agricultural systems management, University of Missouri. “We probably won’t hear much until the end of 2011.”

In the end, regulating air emissions from swine facilities will likely become more stringent. “All large, confinement animal-feeding operations are currently required to notify state officials about ammonia or hydrogen sulfide levels if they emit 100 pounds per day or more of these substances,” Lim says. “I expect to see more EPA regulation on aerial emissions from agricultural facilities.”

While the EPA retains authority to take immediate action against an operation posing a substantial threat to public health, regulations within individual states also may apply more pressure to contain emissions. “In Missouri, for example, Class 1A CAFOs are required to prepare and implement an odor-control plan as described by the Air Pollution Control Program under its odor- emission regulations,” Lim notes.

“There are two main challenges concerning odors for pork producers,” says Richard Nicolai, associate professor, agriculture and biosystems engineering at South Dakota State University:

  • Obtaining local permits.
  • Neighbor complaints and lawsuits.

Of course, site selection and building design provide the best opportunity to prevent odor problems from arising. However, many producers will have to lower emissions output to remain in compliance with facilities that are already in place.

The need for odor-control strategies and mitigation techniques will vary widely among operations and depend on manure-management practices, prevailing wind direction, weather conditions and distance to nearest neighbors.

Biofilters provide a pro-active option offering a cost-effective solution and are relatively easy to design and build. They are used to filter exhaust air from pit fans or wall fans and have become an increasingly used strategy to control odors from swine units. When properly maintained and operated, biofilters can remove 50 percent to 90 percent of odor produced and up to 80 percent of ammonia emissions.

“We have found biofilters to be a very effective means for producers to reduce the odor emitted by deep-pit barn systems,” says Steve Pohl, a biological systems engineer at South Dakota State University. “As far as reducing odor, biofilters are one of our best options.”

Biofilters consist of a structure containing organic material such as wood chips or wood shreds that surround the swine building’s exhaust fans. The filter media supports a microbial population that converts pollutants in the air before the air is exhausted from the filter. Biofilters can be configured as either open or closed beds, though open-bed systems are more prevalent, Nicolai says.

In the search for a small and efficient biofilter, Lim measured emission reduction made possible by pit-fan biofilters employing media at a thickness of 5 inches and 10 inches. He found that the 5-inch biofilters succeeded in reducing ammonia emission by up to 31 percent and hydrogen sulfide by up to 27 percent. The 10-inch filters were found to reduce ammonia emissions by up to 46 percent and hydrogen sulfide by up to 42 percent.

By increasing the contact time of the exhaust air with the media, better results can be achieved. “Biofilters that are designed for 3.5 seconds to 5 seconds of contact time will normally reduce odor and hydrogen sulfide by 85 percent to 95 percent,” Nicolai says.

Since the media needs to be moist for the microbial population to remain active, a wetting system is often needed for optimal warm-weather operation. In northern climates during winter, adding moisture to the media is impractical; however, for the most part there’s usually enough moisture in the exhaust air, Lim says.

Because biofilters require more pressure than simply exhausting air to the environment, some fans may not perform adequately. When biofilters are in use, the resulting drop in static pressure should not exceed 0.1 inch or 0.15 inch of water. Some typical exhaust fans may need to be replaced with fans capable of pushing air through the filter. To determine fan capability, check with the manufacturer. 

When biofilters are constructed, each unit must be sized according to the maximum exhaust output possible from the fan which it covers. “For a biofilter to operate efficiently, the media must provide a suitable environment for microbial growth and maintain a high porosity to allow air to flow easily,” Nicolai says.

When determining how to get the best results for your biofilter investment, Teng suggests pit fans should be the priority. “If a producer were asked to reduce emissions, covering pit fans first probably gives the best bang for the buck.” For a 1,000-head finishing room, Lim estimates the cost to filter three pit exhaust fans at $4,200, using the smaller biofilters.

While cost might vary among operations, the mitigation value is worthy of consideration on its own. “Odor-control technology needs to be considered as a capital cost to do business,” Nicolai says. “For some operations this cost may be zero and for other operations it may be substantial.”

According to Iowa State University odor-control research, biofiltration costs for a 700-sow, farrow-to-wean facility are estimated at 25 cents per piglet, amortized over a three-year life of the biofilter.

“If producers invest in installing odor-control technology on their operations, they may be able to borrow funds to cover those costs and pay them back over the life of the loan,” says Allan Stokes, National Pork Board’s environmental programs director. “For accounting purposes, if the technology was listed as an asset it would likely be amortized over a multiple-year period.  In some instances, producers may phase-in practices and technology over the course of a few years.”

Researchers at South Dakota State University are developing a novel three-step design for a swine barn ventilation system. First, exhausted air is treated to remove the pollutants. Moisture added by the pigs is then removed. Finally, the same air is re-circulated back into the barn. “A small percentage of the re-circulated air is exhausted to the outside atmosphere to remove the carbon dioxide,” Nicolai says. “This system would have near zero emissions and also be able to recover the heat energy.” A final report on the South Dakota State project is expected by early 2011.

Whether you haven’t yet invested in odor mitigation or if you need to upgrade or revise your current efforts, now would be an opportune time. You, and your neighbors, will breathe easier.


Help is Available

Because odor-mitigation practices on swine farms vary by odor source, as well as costs, determining the best control method can be complex. The National Pork Board has a web-based Air Management Practices Assessment Tool that can help you evaluate different options to control odor.

NPB also offers broad-based control options for the three main swine facility odor sources — buildings, manure storage and land application. In addition, NPB offers five brochures that outline various measures and practices you can use to reduce the potential for odor from swine facilities.