For an odor to be detected downwind, odorous compounds must be formed, released to the atmosphere and transported to the receptor site. Inhibit any one of those steps and the odor will diminish. You can use odor-control practices at any of the steps to break the odor event.
Odor is generated in all areas of pork production — animal housing, manure storage and where manure is applied. Some odor-control practices are better suited to some production areas, and most practices are not effective in all areas.
Many of the same compounds that cause odor on a hog farm also affect the indoor air quality inside the buildings. As a result, some odor-reducing practices also improve air quality.
Let’s look at some of the more effective odor-reduction practices and technologies.
Separation Distances: You can control swine facility odors by providing an adequate buffer zone or separation distance from neighbors. Such separation distances can be used to disperse the odor plume. The ideal separation distance between a livestock facility and the nearest neighbor has not yet been determined and it’s somewhat subjective. But in determining the distance, consider the facility size, pig size, manure-management system, prevailing wind direction and topography.
Vegetative Barriers: Landscaping around swine facilities with trees and bushes encourages air mixing and reduces the downwind length of odor plumes. Thick, dense vegetation, especially downwind of the production facility acts as a vegetative filter to reduce dust and disrupt the odor plume.
Vegetative barriers also can provide a visual and aesthetic screen. A well-landscaped pork operation is much more acceptable to the public than one that is not. Naturally the barriers should be designed for the specific location and climate; the plant species selected should intercept odors any season of the year.
Biofilters: These systems provide an environment to trap and biologically degrade odorous gases being exhausted from a barn. Odor reductions at facilities with biofilters have exceeded 90 percent, with similar reductions in hydrogen sulfide (90 percent) and ammonia emissions (75 percent).
Biofilters can be constructed in two configurations — a horizontal bed and a vertical bed. Vertical biofilters place the media in a wall rather than lying it flat and they require a smaller land mass or footprint than a horizontal system.
Biofilters must be designed to provide suitable conditions to promote the growth of aerobic bacteria. Oxygen concentration, temperature, residence time and moisture content are among the parameters that must be considered when building a biofilter. Of particular importance is the media moisture level, as microorganisms require moisture to maintain activity needed to break down the odorous compounds.
Covers: Manure storage covers can be impermeable or permeable. Impermeable covers can be rigid or flexible and tend to have higher cost and a longer lifespan than permeable covers. Rigid covers can be concrete, metal or wood. Flexible covers include geosynthetic thermoplastics and rubber materials such as high-density polyethylene and ethylene propylene diene monomer rubber.
Materials that have been successfully used as permeable covers include straw, lightweight clay balls and geotextile materials. Such covers reduce odor by providing an aerobic layer on top of the manure. As odor passes through the cover, aerobic bacteria break down the odorous compounds.
Diet: About half of the protein in manure is from indigested feed, the remainder being from animal secretions. Because odor production starts with protein decomposition, it’s important that individuals formulating feed consider the composition’s impact on waste production and odor. Options include formulating for lower crude protein, reducing dietary fiber, reducing excreta pH and using compounds such as enzymes that improve feed digestibility.
Management: Feed waste has received little attention as a source of odors. However, feed waste may be responsible for as much as 40 percent of the waste carbohydrates, including virtually all of the easily fermentable ones. Thus, it has the potential to contribute significantly to odor. Proper feeder design, frequent feeder inspection and adjustment, and pelleting the feed are steps that can help reduce waste.
Other Technologies: Other odor-reducing technologies that have shown promise include complete anaerobic treatment, solid and liquid separation, composting solid manure and sprinkling oil in barns. However, these technologies have not yet been widely accepted.
Since each pork operation is unique, the technologies used to reduce odor will be different from a neighbor’s. For example, with open manure storage a cover presents the most practical approach to odor
control. Biofilters have been demonstrated to be effective in reducing odor from buildings. Vegetative barriers provide a practical approach to reduce the odor transported downwind. The key is to
find what combination works for your production site.
Break Down the Technology Barriers
Other than management practices and vegetative barriers, most producers have not adopted odor-reduction technologies because of perceived negative aspects. Such reasons include:
- Cost of implementing the technology. For each technology there is cost associated with purchasing the equipment, labor to install it and maintenance.
- Lack of specific design information in order to adapt the technology to a producer’s unique operation.
- Time and effort required to operate and maintain some of the technologies.
To overcome these barriers the technology or practice needs to offer an incentive that eventually impacts the operation’s profit. Research projects at the University of Minnesota and at South Dakota State University investigated this objective.
The Minnesota project developed a list of critical building design criteria for reducing the environmental footprint while reducing the energy needs.
The South Dakota project developed a practical system that would clean the exhaust air from a swine finishing barn, remove the moisture that the pigs added and recirculate that same air back into the barn. The major advantage of a recirculating-air barn is improved pig performance. Since air speed over the pigs as well as daily and seasonal temperature fluctuation would be minimized, the expected feed efficiency could be 2.2 pounds of feed per pound of gain, helping recover the technology cost.
To evaluate both designs, South Dakota State is raising funds to construct three, 200-head, wean-to finish barns, which would evaluate a reduced-emission barn and a recirculating-air barn. The third one would be a conventional tunnel-ventilated barn, which will serve as a control to determine the efficiencies in pig performance and energy needs to operate the facilities.