Condensed by Milkproduction.com staff from:
BAEU-17 (Nov 1998) from the Department of Bioproducts and Biosystems Engineering, University of Minnesota, USA
Introduction
Reducing the impact of odors on the surrounding community is an essential part of managing livestock and poultry farms. Unfortunately, odor generation, emissions, and movement are very complicated processes. Technologies to reduce odors from livestock production range from simple to complex, from low maintenance to high maintenance, and from inexpensive to expensive. Some have demonstrated odor reduction based on scientific measurements while the effectiveness of other technologies is supported only by anecdotal evidence and testimonials. Anecdotal evidence is useful but should be verified where possible with actual measurements. This document reviews both odor control technologies that have been rigorously tested and others that have yet to be scientifically evaluated but are generally accepted by engineers and/or producers.
Sources of odor
Three primary sources of odor emissions exist for animal production facilities: manure storage units, animal housing, and land application of manure. A 1982 study in the United Kingdom (Hardwick, 1985, Table 1) identified the odor source and animal species from justifiable complaints. Almost 50% of all odor complaints were traced back to land application of manure, about 20% were from manure storage units, and another 25% from animal facilities. Between the three animal species, pigs received slightly more than half (54%) of the complaints, with cattle and poultry receiving 20% and 24% of the complaints, respectively. Even though these findings are from the U.K., general observations in Minnesota and the Midwest seem to agree with this distribution of odor sources. However, increased use of manure soil injection and longer manure storage times (larger manure storage structures), may lead to a higher percentage of odor complaints associated with manure storage units and/or animal facilities.
Research observations at the University of Minnesota document complaints of higher odors from manure storage units during the months of April and May when manure storage units "turn over" as a result of thermal stratification (Jacobson et al., 1997). Limited data exists on odor emissions from animal facilities but these odor emissions are expected to be fairly constant throughout the year, unlike the variable odor emissions from either manure storage units and during the application of manure on cropland.
Most odor control technologies are specific to particular manure handling systems. Therefore, an assessment of an individual farm is needed to determine an appropriate technology for site specific odor sources.
Odor reduction during land application
Land application of manure typically brings about the most complaints. Fortunately, odors from land application can virtually be eliminated by injection or immediate incorporation of the manure into the soil. This also increases the amount of nitrogen and other nutrients available for crop uptake. Injection and incorporation are most easily adapted to liquid manure application. Incorporation of solid manure typically requires another pass with some tillage implement.
Agitation of liquid manure storage facilities prior to manure removal also generates odors. Agitation is necessary to reduce the solids buildup in storage, break up any surface crust, and evenly distribute the nutrients throughout the manure. Reports from many livestock producers suggest that some manure pit additives reduce solids buildup in the storage units. Although there is little university research to support this claim, this technique should be viewed as a possible odor control method. Chemical additives also have the potential to reduce specific gas formation, such as hydrogen sulfide, during agitation for an immediate, short-term effect on gas emissions. Dosage rates and costs for this technology are not well documented.
The issue of reduction of odors and/or certain gases, like hydrogen sulfide, during manure storage agitation is critical. Weather conditions, primarily wind speed/direction and humidity, should be evaluated before manure is land applied to minimize impacts on neighbors and the public. The weather least suitable for spreading manure is high humidity and very light winds or clear, calm evenings. These conditions prevent odors from dispersing and thus increase the chance of creating a nuisance or receiving a complaint.
Odor reduction from manure storage
Manure storage units are the most "apparent" odor source on many farms, especially if there is no visual barrier around the storage system. Open storage systems are the most susceptible to seasonal effects as well as day-to-day weather changes.
Manure storage facilities can be the most significant source of on-farm odors. However, several technologies can significantly reduce odor emissions from manure storage. One way to reduce these odors is with a cover. A cover on a manure storage can act in one of two ways. A gas impermeable cover will capture the gases as they leave the manure. These gases need to be treated using a biofilter, a flare, or some other technique before they are released.
A gas permeable membrane serves to increase the boundary layer between the liquid and air, which decreases the gas emissions to the air. Farmers in the Netherlands have used permeable covers extensively to reduce ammonia emissions from manure storage tanks.
A floating organic cover or crust is a combination of a gas permeable cover and a treatment system. The organic cover increases the boundary layer between the liquid and reduces the gases that are released. An organic cover or crust can develop naturally, depending on the type of feed used, total solids content, and weather conditions, or can be created artificially by using straw or some other organic material.
Anaerobic digestion is a technology that reduces odors from manure storages. Anaerobic digestion controls the microbial degradation process and results in the generation of biogas (primarily methane) which can be used to generate heat or produce electricity (Sweeten et al., 1981). About 15 to 20 days are needed to obtain a treated liquid effluent that is relatively stabilized. The treated material generates significantly less odor than raw manure.
Aeration is another very effective means of controlling odors from stored manure. Aeration of manure accelerates the biological degradation and stabilization process. This is achieved by optimizing the supply of oxygen to microorganisms within the slurry. The odor producing compounds are oxidized and degraded within three to four days of continuous aeration (Svoboda, 1995). Although aeration is very effective at reducing odors, the cost to aerate can be substantial.
Anecdotal evidence suggests that windbreaks may disperse odors released from manure storage. Windbreaks create turbulence in the odor plume, increasing odor dilution. Research from Iowa (Zahn et al., 1997) also indicates that vegetation on trees and other plant material will collect certain odor components released from manure storage units and production sites. Windbreaks and creative landscaping can also reduce the perception of odor by providing a visual barrier.
Odor reduction practices for buildings
Livestock buildings are a source of odors that are often overlooked. Reducing odors from buildings requires control of gas generation or capture of the gases before emission into the atmosphere. Odorous gases are generated from manure soiled flooring, animals, and from any manure stored below the flooring. Each of these odor sources requires different control methods. The best approach to control odor in buildings seems to be eliminating the source of odor rather than capturing the odor and treating it. This means both design and management systems which minimize odor generation on floor surfaces and in manure storage gutters or pits.
In the last 20 or 30 years, animal genetics and ration formulation have improved swine feed conversion efficiencies from 5 lb feed per pound of gain to 2.5 lb feed per pound of gain (Barker, 1998). This improvement means less feed required and less manure produced by a given number of animals. Current U.S. and European research on diet manipulation indicates considerable progress being made in this area.
Modifying animal diets can minimize odors. Research in Europe and the U.S. indicates that reducing the crude protein content of diets (RCP diets) reduces the concentration of odorants and N in the slurry (Hobbs et al. 1996). RCP diets supplemented with synthetic amino-acids to give the ideal ratio of essential amino-acids resulted in reduced N losses and improved utilization following pig slurry application to grassland (Misselbrook et al., 1997). N losses due to ammonia volatilization were also decreased by 35%, compared to conventional diet slurry.
Odor from flooring will be reduced if the floors are kept clean and dry. Anecdotal evidence suggests that some organic bedding, straw, compost, or newspaper may reduce odor emissions. European research seems to support the use of some type of bedding (especially sawdust) for reducing odor generation/levels in buildings and subsequent odor release or emission (Nicks et al., 1997). Relatively small bedding levels may be enough to have an effect on odor generation/emission. Recent preliminary research in Canada (Zhang et al, 1996) and in Minnesota (Jacobson et al., 1998) showed odor emission reductions when very small amounts of vegetable oils were sprinkled in swine pens on a regular (daily) basis. This practice was developed to reduce indoor dust levels and since particulates may transport odorous compounds, odors may be reduced as well.
Control of odors from under floor manure storage depends on the type of manure storage. Manure stored longer than five days will generate more offensive gases. Therefore, to reduce odors from gutters with shallow pull plugs, the manure should be removed at least once per week. Weekly cleaning is frequently not a standard practice but may become so if odor control is the main objective. One method of shallow gutter management for odor control that is still under debate is the practice of using recharge water. Some facilities use clean recharge water, some recycle recharge water, and others do not recharge their shallow gutters. Anecdotal evidence suggests that using clean or "treated" recycled recharge water may reduce odorous emissions compared to using no recharge water. However, these reductions are likely to be very dependent on the quality of recharge water.
Few options exist to reduce odor generation from manure stored below the barn in deep pits. A Canadian study (Choiniere et al., 1997) found that odor emissions could actually be increased by certain types of pit ventilation systems. A balance exists between maintaining good indoor air quality and minimizing the emissions of odor to the environment.
Odors from buildings can be captured and treated, provided that the building is mechanically ventilated. Passing air from a livestock building through a biofilter (a bed of organic material where aerobic microbial activity takes place) can convert odorous gases into non-odorous by-products. Biofilters have successfully treated exhaust air from industrial processes and wastewater treatment plants. University of Minnesota research suggests that low-tech biofilters are effective and economical for agricultural uses.
Odor management plans
Just as manure management plans have become standard practice, in the near future, a similar "odor management plan" may be needed by animal producers to indicate what control technologies and strategies will be implemented to reduce odors emitted from a livestock or poultry farm.
Such plans need to systematically list each of the potential odor sources from a particular farm including the three sources outlined in this paper: manure land application, manure storage units, and buildings plus the farm's dead animal disposal method. After this inventory is taken, each building, storage unit, application method, and carcass disposal system would need to be assessed for odor potential. If a particular source has an odor potential above a given "threshold" level, even for a short period of time during the year, some control strategy(s) would be suggested and implemented to reduce the odor emissions to a reasonable level. Control strategies could be technologies like those listed in Table 2, management practices, or a combination of both.
Like the manure management plans, odor management plans could be optional or in some cases required as part of the permitting process. Such plans may diffuse some of the controversies between producers and neighbors by directing the discussion to strategies and practices to mitigate the problems.
Knowledgeable individuals to make these assessments and develop odor management plans are in short supply at the present time. As odor research and application of that research becomes available, more people will be able to make these decisions and assessments.
Summary
The debate will continue on how much odor control is enough. However, one fact remains, odors from animal production systems must be reduced in order for producers to remain in business and still coexist with neighbors and the community. Several technologies are currently available to reduce odors, unfortunately, economics often prohibit such technologies from being implemented. Currently, there is a substantial effort by university researchers, industry representatives, and producer groups to find and implement odor control technologies. These efforts can be enhanced through the efforts of everyone involved in the livestock industry. Producers, engineers, technicians, consultants, veterinarians, nutritionists, and others must combine their expertise with the basic principles of odor generation, emission, and dispersion to develop and implement practical odor control solutions.
Table 2. (For a large table click here >>)
*Potential nuisance risk is currently a subjective rating based on common sense, experience, and an understanding of how odors are generated. Most farm operators and owners are capable of making these decisions.
Table 3. Summary of Odor Control Technologies
Summary of Technologies for Odor Control (for a larger table click here>>)
References
Barker, J. C. 1998. Swine environmental issues: snowballing legislation and manure management-where are we headed? In Biotechnology in the Feed Industry (T.P. Lyons and K.A. Jacques, eds.), Nottingham University Press, 81-92.
Choiniere, Y., B. Marquis and G. Gingras. 1997. Ammonia and Contaminant Concentrations with Conventional versus Pit Ventilation in Finishing Pig Units. pp. 365-372. In Proceedings of the International Symposium on Ammonia and Odour Control from Animal Production Facilities. (Voermans, J.A.M. and Monteny, G. editors). Research Institute for Pig Husbandry, Rosmalen, Netherlands.
Hardwick, D. C. 1985. Agricultural problems related to odor prevention and control. pp. 21-26. In Odor Prevention and Control of Organic Sludge and Livestock Farming. Edited by V. C. Nielsen, J. H. Voorburg, and P. L'Hermite. Elsevier Applied Science Publishers, New York.
Hobbs, P. J., B. F. Pain, R. M. Kay and P. A. Lee. 1996. Reduction of odorous compounds in fresh pig slurry by dietary control of crude protein. J. Sci. Food and Agric. 71: 508-514.
Jacobson, L. D., C. Radman, D. Schmidt, and R. Nicolai. 1997. Odor Measurements from Manure Storages on Minnesota Pig Farms. Proceedings of the ILES-V. May 29-31. Bloomington, MN pp. 93-100.
Jacobson, L. D., B. Hetcher, K. A. Janni and L. J. Johnston. 1998. Odor and Gas Reduction from Sprinkling Soybean Oil in a Pig Nursery. Presented at the 1998 ASAE Annual Inter. Meeting in Orlando, FL., St. Joseph, MI. USA.
Misselbrook, T. H., D. R. Chadwick, P. J. Hobbs and B. F. Pain. 1997. Control by dietary manipulation of emissions from pig slurry following landspreading. Procs. of the Intl. Symp. on Ammonia and Odour Control from Animal Production Facilities, Vinkeloord, The Netherlands, October 6-10. pp. 261-266.
Nicks, B., A. Desiron and B. Canart. 1997. Deep Litter Materials and the Ammonia Emissions in Fattening Pig Houses. pp. 335-342. In Proceedings of the International Symposium on Ammonia and Odour Control from Animal Production Facilities. (Voermans, J.A.M. and Monteny, G. editors). Research Institute for Pig Husbandry, Rosmalen, Netherlands.
Svoboda, J. F. 1995. Aerobic Treatment of Livestock Slurries. SAC Technical Note, Environmental Series No. 2.
Sweeten, J. M., C. Fulhage and F. J. Humenik. 1981. Methane Gas from Swine Manure. Pork Industry Handbook (PIH-76). Purdue University, West Lafayette, IN.
Zahn, J. A., J. L. Hatfield, Y. S. Do, A. A. DiSpirito, D. A. Laird, and R. L. Pfeiffer. 1997. Characterization of Volatile Organic Emissions and Wastes from a Swine Production Facility. J. Environ. Qual. 26(6).
Zhang, Y., A. Tanaka, E. M. Barber and J. J. R. Feddes. 1996. Effect of frequency and quantity of sprinkling canola oil on dust reduction in swine buildings. Transactions of American Society of Agricultural Engineers, 39(3): 1077-1081.
University of Minnesota, U.S. Department of Agriculture, and Minnesota Counties Cooperating
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