Some livestock operations are becoming larger. As a result, odor and dust from livestock operations have become an increasing concern for farmers and their neighbors. Control of odors and dust is becoming a necessity for farmers to maintain the sustainability and profitability of their livestock operations.
Odor and dust control are affected by factors such as biological characteristics of the farm animals, animal density and scale of operation, management practices, topography, distance from neighbors, weather conditions, people’s perception and tolerance to odor and dust, and governmental regulations.
Although it is difficult to eliminate odor and dust emissions from livestock operations, there are many ways to reduce the emissions. This chapter provides information on odor and airborne dust and the means to reduce odor and dust emissions. Appendix J describes methods of measuring odor.
Odor is an unpleasant smell caused by emissions of odorous compounds. Anaerobic decomposition/transformation of livestock and poultry manure by microorganisms generates the odorous compounds. Metabolic processes within the gastrointestinal tract of livestock also generate some of the odorous compounds. More than 160 volatile compounds have been identified as contributors to odor from confinement facilities. These compounds include ammonia, hydrogen sulfide, mecaptans, fatty acids, and amines, to name a few. Because of the vast number of compounds contributing odor, their individual contribution under various conditions is not yet clear.
Dust is the airborne particulate emission from livestock operation and typically consists of manure solids, dander, feathers, hair, and feed. Dust particles are carriers of odor, toxic gases, endotoxins, and pathogens. Dust is measured as mass concentration in air (mg/m3) by gravimetrical filter method, or numbers of particle per volume of air (particles/m3) by electronic particle counters.
Air temperature, relative humidity, manure accumulation time, ventilation of the production buildings, weather conditions, and dust level affect odor generation, transportation, and human perception. High temperatures speed biological processes and can increase odor emissions. High humidity and moisture levels promote anaerobic decomposition of organic compounds and in turn generate more odors. Manure accumulation time affects total odor generation. Weather conditions affect the spread of odors. Ventilation systems in production buildings reduce odor levels within the structure. Dust is known as a major odor carrier. Dust levels correlate well with odor levels.
Livestock facilities have three major sources of odor and dust:
Of these sources, odors are likely from all three sources while most dust emits from the animal-production buildings. There are many other minor odor sources on a farm, such as the animal’s breath, flatulence, dirty coats, milking center, feed room, etc.
Basic concepts for odor control at an animal production facility are:
Considerations to minimize odor and dust when building new or expanding facilities include:
There is no absolute standard separation distance, but location of buildings should be considered. Odor sources should be located downwind of other buildings to maintain a better living environment for farmer and animals.
Because odor is often visualized (perception), good landscaping around the farm, especially around odor sources, can reduce complaints about odor. In addition, the landscaping can help change the odor and dust dispersion patterns and dilute the polluted airstreams.
Manure, wet feed, and dust generate odor and should be removed regularly. Keeping the floor surface, wall, and animals dry and clean will reduce odor. Manure temporarily stored in the facility should be removed at least once a week as manure stored longer than five to seven days generates more offensive gases. For swine, if a pull-plug system is used, recharge the manure pit with clean or treated water to reduce the odor generation rate.
Solid manure systems usually generate less odors compared to liquid manure systems. Using some type of bedding can reduce odor generation in buildings. Odor control effectiveness is one of the reasons that hoop structures are currently become popular among swine and dairy producers. High-rise buildings for swine production and the litter system for broilers and turkeys effectively manage odor problems.
Diet manipulation to minimize odor is becoming an accepted concept. Research has shown that manipulation of feed additives, level of protein, and other nutrients in an animal’s diet may affect the potential odor and gas emissions from animal manure. However, the quantitative effects of diet manipulation on odor and gas reduction and animal performance are still being determined along with its effects on the quality of egg, meat, and milk products.
Proper ventilation supplies fresh air into the buildings and prevents anaerobic decomposition of organic materials and in turn reduces odor generation. Fresh air also dilutes odorous air in buildings. In addition, proper ventilation is also critical to the animals’ health and productivity.
Airborne dust is known as a carrier of odor and toxic gases. Research has shown that sprinkling vegetable oil is one way to reduce dust concentration in animal buildings. Under some conditions, daily sprinkling reduced the dust level by 80%; hydrogen sulfide concentration, 20%; and ammonia concentrations, 30%. However, sprinkling can lead to other management issues, such as the coating of equipment and building surfaces. For detailed information on how to sprinkle vegetable oils in hog barns, please refer to MWPS publication AED-42.
Ozone is a powerful oxidizer and an effective natural germicide. Ozone has been used to treat drinking water on a municipal scale. Research at Michigan State University has shown that applying ozone at concentrations of 1 to 3 mg/l to fresh or stored swine manure reduced odor emission significantly. More studies are needed to evaluate ozone effectiveness and economics.
Wet scrubber technologies are widely used in the chemical and mining industry and are recognized for being able to not only reduce dust emission but also to reduce water-soluble gases. The technology has been applied to the animal production industry. Evaporate cooling pads in tunnel ventilation systems can serve as a wet-wall to scrub 60% dust at low ventilation rates and 20% dust at high ventilation rates. The wet pad had minor odor reduction— 50% ammonia reduction at low ventilation rates and 33% ammonia reduction rate at high ventilation rates (Bottcher, et al., 1999).
A wet scrubber developed for swine exhaust air has 84% dust collection efficiency and 90% water recovery (Zhao, et al., 2001). Because the current odor intensity measurement method does not take into account odors carried by dust particles, the odor reduction efficiency of the wet scrubber mentioned earlier is not significant using the current odor measurement method. However, the wet scrubber is believed to have great potential to reduce dust, gases, and odor. Further development of low-cost and efficient wet scrubbers for agricultural buildings is being conducted.
A deduster is a device to clean dust in animal buildings. The particle separation efficiency of the deduster reaches 90% for particles larger than 10 µm and 77% for particles larger than 7 µm. In terms of mass concentration measured using mass samplers, the particle separation efficiency reached 85% (Zhang, et al., 2001). The deduster could be an effective method for air cleaning of dusty airspaces, such as livestock and poultry buildings.
Biofiltration uses microorganisms to break down gas contaminants to non-odorous products using a biofilter media. The filter media can be ground yard trimmings, compost, corncobs, chopped cornstalks, and other organic materials. Air to be treated is slowly passed (minimum resident time of 10 seconds) though a biologically active bed of material, generally 1.5- to 3-feet deep. The odor reduction rate can reach 80% to 90% for odorous organic compounds in properly maintained systems. Hydrogen sulfide and ammonia have also been reduced as much as 50% or more. Recent studies indicate that the construction and operating cost of a biofiltration system is about $0.22 per pig produced per year. In addition, there is a $400 cost associated with extra energy requirement and rodent control (Nicolai and Janni, 1998 b, c).
Windbreaks redirect the exhaust air from animal buildings upward to prevent the direct movement of odors and dust onto neighboring properties. They could be artificial walls or natural trees and vegetation. Typically, windbreaks are placed 10 to 20 feet downwind of the exhaust fans of tunnel-ventilated barns. For naturally ventilated buildings, windbreaks should be placed at least 100 feet, or 10 times the windbreak height, from the buildings to prevent blockage of cooling breezes and air exchange.
Research shows some effect of windbreaks on odor reduction, but the exact effectiveness has not been assessed yet. Snow deposition concerns should be evaluated during the windbreak planning to ensure snow drift will not be deposited next to or on the barn.
Manure storage facilities are significant sources of odor on a farm. There are several ways to reduce the odor emission from a manure storage and handling site.
A logical method to reduce odor emission from open manure storage is to cover the manure storage space. There are many different kinds of covers to reduce odor emission—concrete and wood impermeable covers, plastic impermeable covers, and floating permeable covers. Rigid covers are more expensive and are expected to last 10 to 15 years. Depending on the materials used, the cost of rigid covers varies considerably. Plastic covers can be inflatable over the lagoon or floating over the manure surface. The cost is about $100 per liner foot of diameter. The lifetime is about 10 years. Research shows that floating plastic covers are easier to maintain than the inflatable ones.
Floating permeable covers can be formed naturally or artificially. Natural covers usually are formed by the fibrous material in the manure. Artificial covers can be formed by organic materials such as barley straw, wheat straw, chopped cornstalks, sawdust, wood shavings, and rice hulls. Man-made materials, such as Polystyrene foam, plastic mats, air-filled clay balls, and geotextiles, also can be used as floating permeable covers.
Research by the University of Minnesota indicated that permeable covers are more suitable for odor reduction than impermeable covers. Layers of straw in four-inch, eight-inch, and 12-inch-deep layers can reduce odor 60%, 80%, and 85%, respectively. The odor and gas emission reduction efficiencies of permanent roofs of wood, concrete, and plastic covers can be as high as 80% for odor and 80% to 95% for ammonia (Hoff, et al.).
In summary, covers can significantly reduce odors from the manure-storage facilities. When selecting a cover, consider the size and type of manure-storage system, the type of manure-treatment system, the frequency of pumping, the cost and lifetime of the cover, the maintenance required, and the ease to operate.
Aerobic treatments aerate manure to prevent anaerobic decomposition by adding oxygen. Complete aerobic treatments can eliminate manure odors. The treatment can be an aerobic reactor or aerated lagoon. The drawbacks of aerobic treatment are high energy cost, high bio-solids production, and the potential for release of ammonia and other gases if the aeration is not controlled well. The high operating cost prevents aerobic treatment from being widely used by producers.
Anaerobic treatment of manure treats manure without oxygen. The typical anaerobic treatment is an anaerobic lagoon, either one-stage or two-stage lagoon system. When an anaerobic lagoon is properly sized and managed, odor emission can be reduced significantly. However, nitrogen gases are natural byproducts of anaerobic decomposition.
Anaerobic digesters are another anaerobic treatment alternative. Compared with the anaerobic lagoon, the decomposition processes can be well controlled in an anaerobic digester and thus are more efficient. One of the most common anaerobic digesters is the plug-flow reactor. Others include complete-mix, contact, and up-flow anaerobic sludge blanket digesters. Very little odor is produced from a properly managed anaerobic digester.
Odor reduction from land-spreading treated manure can be 70% to 80% compared to spreading untreated manure slurry. However, proper design, construction, and operation of an anaerobic digester are critical to the success and wide application of the system. See Chapter 4, Treatment and Utilization Options for Livestock Manure, for more information on anaerobic lagoons. For more detailed design of anaerobic lagoons, please refer to MWPS-18, Livestock Waste Facilities Handbook.
Composting is a biological process in which microorganisms convert organic materials, such as manure, sludge, and leaves, into a soil-like material called compost. Composting treatment is applicable to solid or semi-solid manure. Composting can reduce manure volume, stabilize manure nutrients, kill pathogens and weed seeds, and produce a homogeneous non-odorous product.
If operating conditions are managed properly, carbon dioxide and water vapor will be the primary gases emitted during the composting process. In addition, compost is a value-added material. For detailed information about the composting process, please refer to NRAES 54, On Farm Composting Handbook.
Many biological and chemical additives for manure are on the market. The performance of various manure additive products is still not reliable. Currently, it is still difficult to justify the balance between the odor reduction effect and the cost associated with the additive products.
Odor perception is a human subjective response and is affected by visualization. If proper landscaping is designed and maintained, odor conflicts with neighbors can be reduced. Landscaping physically changes the odor dispersion pattern, provides a large filtration surface for odorous compounds and dust, and forces more dilution to the odorous air stream.
Land application of manure returns nutrients and organic matter to the soil. It also is the most frequent source of odor complaints from the public. Therefore, how, where, and when to apply manure all affect odor dispersion and odor complaints. Alternatives to reduce the odor emission during land application of manure include:
Odor emissions are affected by the surface area of the manure that contacts the air. Applying manure beneath the soil surface by injection or by covering it immediately after surface application, called incorporation, eliminates most of the odor. Injection is the most effective way to reduce odor during the land application of untreated manure. In addition, manure injection and incorporation can also reduce manure nitrogen losses by reducing ammonia volatilization. Field research shows a 90% odor and ammonia reduction by shallow or deep manure injection compared with surface application. Incorporation after spreading also reduces the odor level and nitrogen losses, but not as efficiently as injection.
The common injectors on the market are narrow tines, sweeps, disk injectors and covers, and conventional chisel plows. When selecting an injector, system power consumption is another important factor to consider. Generally, newer injectors, such as disks and sweeps, use less power and distribute the nutrients better.
Surface application using drop holes, which apply manure liquid on the surface through a series of drop holes close to the surface, has proved to be an effective odor control practice in Europe. Placing the manure on the surface but beneath the crop canopy also helps to control odor emission.
Applying liquid manure by spray or surface irrigation systems remains a popular method to distribute manure. This method produces considerable odor if the manure is not treated. Means to reduce odor are:
When applying manure, always consider time, weather conditions, and location constraints. Try to avoid applying manure while the wind is blowing towards your neighbors. Build good communications and relationships with your neighbors to minimize misunderstandings and complaints. Make an effort not to apply the manure during weekends, holidays, and any other special event days.
Odor and dust emissions can become limiting factors for the sustainability of animal production. Understanding sources of odor, perception of odor, and current technologies to reduce odor are the first steps to control odor. Producers should use professional help to develop a comprehensive odor and dust-control plan, considering all aspects of the production and combination of odor-control efforts. Odor and dust control is a complex issue. It is difficult to eliminate odor and dust emissions completely from livestock operations. However, many technologies are available to reduce the emissions to an acceptable level, and new technologies are being developed to help producers control odor and dust efficiently.
Bottcher, R. W., K. M. Keener, R. D. Munilla, K. E. Parbst, and G. L. Van Wicklen. 1999. Field evaluation of a wet pad scrubber for odor and dust control. Animal Waste Management Symposium, Raleigh, N.C., January 27-28, 1999.
Elenbass A., L. Y. Zhao, Y. Young, G. L. Riskowski, and M. Ellis. 2001. Effects of Ozonation on Odor, Dust, and Gaseous Emission Control and Pig Growth Performance. ASAE Paper No. 01473, American Society of Agricultural Engineers. St. Joseph, Mich.
Hoff, S. J., L. Dong, X. W. Li, D. S. Bundy, and J. D. Harmon. 1997a. Odor removal using biomass filter. Proceedings of the 5th International Symposium on Livestock Environment, Bloomington, Minn., May 29-31, 1997, 2:101-108.
Livestock and Poultry Environmental Stewardship (LPES) Curriculum, module lessons at www.lpes.org)
MidWest Plan Service, MWPS 18, Livestock Waste Facilities Handbook.
NWPS Agricultural Engineers Digests, AED-42.
Nicolai, R. E. and K. A. Janni. 1998a. Comparison of biofilter residence time. ASAE Paper No. 984053. American Society of Agricultural Engineers. St. Joseph, Mich.
Nicolai, R. E. and K. A. Janni. 1998b. Bio-filtration technology for odor reduction from swine buildings. In Proceedings, Animal Production Systems and Environment Conference, Iowa State University, Ames.
Rynk, R., Editor. On Farm Composting Handbook. NRAES 54. 1992. Natural Resource, Agriculture, and Engineering Service (NRAES), P. O. Box 4557, Ithaca, NY 14852-4557, www.nraes.org.
Zhang, Y., X. Wang, G. L. Riskowski, L. L. Christianson, and S. E. Ford. 2001. Particle separation efficiency of a uniflow deduster with different types of dusts. Transactions of Amer. Soc. Heat. Refrig. Air Cond. Engr. 107(2): 93-98.
Zhao, L. Y., G. L. Riskowski, P. Troot, and M. Robert. 2001. Development of a Wet Scrubber to Reduce Odor and Dust Emissions from Swine Buildings. ASAE Paper No. 014075. American Society of Agricultural Engineers. St. Joseph, Mich.