Intensive animal feeding operations emit sufficient odor, ammonia, hydrogen sulfide, volatile organic compounds, greenhouse gases and particulate matter (PM) to have a significant effect on air quality, requiring abatement solutions (USDA, 2000; Monteny and Voermans, 1998). Whereas NH3 and greenhouse gas emissions have been the primary abatement goal in Europe, odor control is presently the highest priority of U.S. livestock production. Ammonia volatilization used to be considered in the U.S. as a means to balance N for land application, but is now being viewed as an air quality problem. Dust emission reduction has recently become an important goal for agriculture in both North America and Europe. Regulations in the U.S. have begun to include phosphorus and pathogens in water quality goals and PM, odor and NH3 in air quality goals. Greenhouse gas emissions have not received as much attention in the U.S. as in Europe. However, since CO2, CH4 and N2O are natural products of manure decomposition, strategies to reduce emissions of odor and odorants are likely to reduce emissions of these gases as well (USDA, 2000).
Table 1 summarizes abatement technologies that may reduce pollutants from livestock facilities. Some of these technologies have been sufficiently tested to prove their efficacy, but most have not been evaluated properly or systematically. Producers, researchers and advisors must realize that measures implemented in one part of the operation may increase emissions from the overall operation. For example, pull-plug manure pits drained frequently to reduce building emissions could increase overall emission from the operation if the drained manure is not properly handled, stored, and treated. Also, deep litter systems reduce NH3 emissions but increase emissions of greenhouse gases. Well?managed straw bedding systems reduce building NH3 emissions but overall emissions to the atmosphere are the same because of higher losses during storage and spreading. Also, more dust is emitted with straw bedding.
Building emissions can be significantly reduced through proper management of manure, ventilation, feed and building hygiene. For example, emission reduction from poultry houses is achieved by frequent and complete removal of droppings from layer houses, by continuous litter ventilation and drying in houses with birds on litter, and by using pit circulation fans to promote drying of droppings in caged-layer houses (van Horne et al., 1998). Reducing moisture content of litter is critical especially for reducing emissions during outdoor storage. The "fill and empty" principle of manure removal in pig houses produces 70% less NH3 than fully slatted floors with deep pit and long?term storage (Oosthoek et al., 1990).
Diet modification (phase and split-sex feeding, Yucca-extracted sarponin, reduced crude protein, added fiber, etc.) continues to be regarded as having the most potential for economically improving the nutrient cycle of livestock systems (Sutton, 1999). Research has shown significant reductions of NH3, odors, and greenhouse gases during storage and land application of slurry (Hartung and Phillips, 1994). These effects are attained by reduced concentration in the slurry of total and NH4-N and slurry pH, whereas effects on odor emission are probably more related to reduced concentration of volatile fatty acids (Monteny and Voermans, 1998). Minimizing sulfur-containing amino acids and mineral sulfates reduce sulfur-based gases. Adding soybean oil or animal fat to diets or using high-oil maize in the diets reduces dust emissions (Jacobson et al., 1998).
Treatment of liquid manure in pits is used to develop aerobic conditions, enhance anaerobic conditions, or stop microbial activity. Aerobic systems are very effective but involve high energy and maintenance costs. Chemical (organic and inorganic acids) and biological (enzymes, microorganisms) additives have been used to abate emissions, but very few independent tests have proven their effectiveness. However, Berg (1998) reported that lactic acid reduces methane and nitrous oxide emissions by 80 to 90% and that the benefits of acidification extend not only to the animal house, but also to manure storage and land application.
Air treatment systems can remove multiple pollutants, and low-cost designs are possible. Biofiltration is an aerobic process that breaks volatile compounds into CO2, water and mineral salts. In one study using compost and dark red kidney bean straw for a biofilter bed, farrowing house odors from a pit fan were reduced by 78% and NH3 by 50% (Nicolai and Janni, 1997). In another study, gestation/farrowing house odors were reduced by 95% and H2S by 90% (Nicolai and Janni, 1997). The cost was US$0.22 per pig produced in the gestation/farrowing facility. Innovative designs are being developed to reduce the initial cost and to minimize operating costs and labor. Biofilters are only really applicable to fan-ventilated buildings.
Dust removal techniques also reduce gas and odor emissions because gases adsorb onto the particles. Low maintenance aerodynamic dedusters have removed 80% of odorous dust from swine house exhaust air in university tests. This experimental method requires more field testing but does show potential for removing multiple pollutants. One promising technology for reducing building emissions is sprinkling of oil/water mixtures on surfaces (floors, animals, feed, straw) to keep settled dust from resuspending into the air. About 50% reductions in odors have been shown. Cost is estimated at US$1.15 per pig marketed, with 70% of the cost in labor (Banhazi et al., 2000). More field research is needed to solve some practical problems associated with oil sprinkling.
Windbreak walls near the exhaust fans (Bottcher et al., 2000) and woodlands further away may remove some of the dust and deflect odorous air upward for better atmospheric mixing. However, the effectiveness of these artificial and natural barriers has not yet been well quantified.
Outdoor Manure Storage, Handling and Treatment
Abatement measures for manure storage and treatment facilities depend greatly on site-specific factors (Monteny and Voermans, 1998). For example, covering storage facilities (silo, tank, lagoon) is beneficial when manure can be utilized on the farm whereas manure treatment is useful when there is a nutrient imbalance.
Permeable covers are utilized by many North American livestock producers on anaerobic treatment basins (lagoons) and open manure storages (PSF, 2000). Such covers limit solar heating and wind-induced volatilization. Permeable covers have high surface contact areas and provide an aerobic zone for degradation of odors and other gases emitted from the slurry. Permeable covers and biocovers including chopped straw, cornstalks and geotextile materials provide 50-90% emission reduction. Manufactured materials in the form of self-dispersing granules or powder have resulted in over 95% reductions in odor, NH3, and H2S emissions, according to laboratory tests. The product floats back to the surface after agitation. Peat moss and light expanded clay aggregate (LECA) are also very effective but cost US$2.90 and US$9.68 per square meter, respectively. Impermeable floating plastic covers result in over 99% emission reduction (Jacobson et al., 1999).
Anaerobic digestion systems are very effective air and water pollution control systems and appear to represent the wave of the future for livestock production in the U.S. They pretreat high strength wastewater to reduce biosolids volume and control wastewater system odors (PSF, 2000). Initial capital costs are high but utilization and sales of energy and composted manure solids can provide paybacks of 5 to 7 years. Anaerobic digesters have recently been installed on several large livestock farms in the U.S. and have been shown to:
1. Reduce odor from land-applied slurry by 75%,
2. Enable the sale of electricity and provide a heat source to the farm
3. Maintain the manure's fertilizer value (Pigg and Vetter, 1984),
4. Improve handling and solids separating characteristics of manure,
5. Stabilize manure by converting up to 70% of organic N into NH4-N,
6. Destroy about 60 to 75% of the volatile solids,
7. Conserve water and produce marketable digester "fiber",
8. Reduce transportation costs by reducing manure solids by 70 to 95%,
9. Reduce BOD levels by up to 90% and COD by 60-70% (AgSTAR, 1997),
10. Reduce odor and gas emissions,
11. Destroy weed seeds and reduce pathogens by more than 99%,
12. Reduce attractiveness of the manure to rodents and flies.
Covered lagoon digesters (NRCS, 1996) are increasing in popularity in the U.S. as a technique to control odor. They are essentially an inefficient digester, because temperature and mixing are not controlled. Biogas is collected and either released to the atmosphere, burned in a flare, or utilized to heat on-farm processes or generate electricity (Safley and Westerman, 1994). They are capable of capturing 0.25 to 0.60 m3 CH4 per kg volatile solids (Cheng et al., 1999).
Composting, a biological treatment technique, is possible for all solid manures. Composting reduces weed seeds and pathogens. About 20 to 40% of the total N in the solids is emitted as NH3 and about 1 and 2% as N2O and CH4, respectively. Optimized C/N ratios reduce NH3 emission (Jacobson et al, 1999).
Innovative emission abatement during land application of slurry includes direct ground injection and incorporation. These techniques are commonly practiced in many countries to improve retention of nutrients, and to reduce NH3 and odor emissions (Monteny and Voermans, 1998).
Recent Emission Abatement by Large Swine Producer in Missouri
A Consent Decree in 1999 required a large U.S. pork producer Premium Standard Farms (PSF) to develop and implement plans to investigate and implement new technologies that reduce odors and nutrients, reduce effluent volumes and reduce the risk of spills during land application. PSF has facilities for 107,000 sows and 800,000 finishing spaces in the State of Missouri (PSF, 2000) that include 163 single stage anaerobic treatment lagoons. Most of their barns are mechanically ventilated and have shallow flush gutters beneath the fully slatted floors. Lagoon effluent is land applied using high-pressure traveling gun applicators. PSF has recently implemented windbreak walls, permeable covers, aerobic polishing, nitrogen reduction cells and low-emission land application techniques (low-pressure irrigation, subsurface injection) at their pork production sites.
1. Develop effective, practical and economically feasible emission control technologies for confined animals, treatment, and land application systems.
2. Develop potential relationships between emission constituents, concentrations, and potential health indicators, and devise appropriate mitigation strategies accordingly.
3. Test effects of slurry acidification in animal houses (Hornig et al., 1997).
4. Determine how additives affect emissions from slurries.
5. Evaluate effects of abatement techniques on each target pollutant.
6. More research is needed on biofilter maintenance, dust removal, and disposal of saturated material.
7. Develop ways to dispose of wet scrubber wastewater.
8. Develop better knowledge of how abatement methods for different pollutants interact.
9. Standardize reliable emission measurement methods.
10. Develop economic models to evaluate cost-effective abatement strategies (Cowell and ApSimon, 1998, Phillips et al., 1998).
AgSTAR. 1997. A Manual for Developing Biogas Systems at Commercial Farms in the United States (Roos, K.F. and M.A. Moser, Eds.), U.S. EPA.
Banhazi, T., C. Cargill, G. Marr, A. Kefford, K. Moore and S. Koch. 2000. Relating Airborne Pollution To Management And Housing Factors. Project No. DAD 39/1202, Final Report to the Pig Research and Development Corporation, Australia, March.
Berg, W. 1998. Emissions from animal husbandry and their assessment. Proceedings of the 13th CIGR International Congress on Agricultural Engineering, Rabat, Morocco, February 2-6, pp. 289-295.
Bottcher, R.W., K.M. Keener and R.D. Munilla. 2000. Comparison of odor control mechanisms for wet pad scrubbing, indoor ozonation, windbreak walls, and biofilters. ASAE Paper 00-4091, ASAE, St. Joseph, MI 49085.
Cheng, J., K.F. Roos and L.M. Saele. 1999. Covered anaerobic lagoon system for swine waste treatment of energy recovery. ASAE Paper 99-4048, ASAE, St. Joseph, MI 49085.
Cowell, D.A. and H.M. ApSimon. 1998. Cost-effective strategies for the abatement of ammonia emissions from European agriculture. Atmospheric Environment 32(3):573-580.
Jacobson, L.D. et al. 1999. Literature Review for Air Quality and Odor. Topic IIIH of Generic Environmental Impact Statement prepared for the Minnesota Environmental Quality Board, June 22.
Hartung, J. and V.R. Phillips. 1994. Control of gaseous emissions from livestock buildings and manure stores. Journal of Agricultural Engineering Research 57:173-189.
Hörnig, G., W. Berg and M. Türk. 1997. Harmful gas and odor emissions under use of feed and slurry additives. Proceedings of the Fifth International Symposium on Livestock Environment, Bloomington, MN, May 29-31, pp. 78-85.
Jacobson, L.D., B. Hetchler, K.A. Janni and L.J. Johnston. 1998. Odor and gas reduction from sprinkling soybean oil in a pig nursery. ASAE Paper No. 98-4125, ASAE, St. Joseph, MI 49085.
Monteny, G.J. and J.A.M. Voermans. 1998. Ammonia and odour control from animal production facilities: review of the international symposium held at Vinkeloord, The Netherlands, October 6-10, 1997, pp. 295-301.
Nicolai, R.E. and K.A. Janni. 1997. Development of a low-cost biofilter for swine production facilities. ASAE Paper No. 97-4040, ASAE, St. Joseph, MI 49085.
Nicolai, R.E. and K.A. Janni. 1998. Biofiltration - technology for odor reduction from swine buildings. In: Animal Production Systems and the Environment: An International Conference on Odor, Water Quality, Nutrient Management and Socioeconomic Issues, Des Moines, IA, USA, pp. 327-332.
NRCS. 1996. Covered Anaerobic Lagoon. Code 360. Service Interim Conservation Practice Standard, Natural Resources Convervation Service, Washington, D.C.
Oosthoek, J., W. Kroodsma and P. Hoeksma. 1990. Methods of reducing ammonia emissions from animal housing. In: Ammoniak in der Umwelt (Hartung, J., M. Paduch, S. Schirz, H. Döhler and H. van den Weghe, Eds). Landwirtschaftsverlag GmbH, Münster, Germany 29:1-23.
Pain, B.F., Phillips, V.R., Clarkson, C.R., Misselbrook, T.H., Rees, Y.J. and Farrent, J.W. 1990. Odour and ammonia emissions following the spreading of aerobically treated pig slurry on grassland. Biological Wastes 34:149-160.
Phillips, V.R., D.A. Cowell, R.W. Sneath, T.R. Cumby, A.G. Williams, T.G.M. Demmers and D. Sandars. 1998. Report to MAFF on Project No. WA 0640. Silsoe Research Institute, Wrest Park, Silsoe, Bedford MK45 4HS, U.K.
Pigg, D.L. and R.L. Vetter. 1984. Fertilizer content of anaerobically digested dairy cow manure. ASAE Paper No. 84-2110. ASAE, St. Joseph, MI 49085.
PSF. 2000. Environmental Work Plan. Premium Standard Farms, Inc., March 24.
Safley, L.M. Jr. and P.W. Westerman. 1994. Low-temperature digestion of dairy and swine manure. Bioresource Technology 47:165-171.
Sutton, A.L., K.B. Kephart, M.W.A. Verstegen, T.T. Canh and P.J. Hobbs. 1999. Potential for reduction of odorous compounds in swine manure through diet modification. Journal of Animal Science 77:430-439.
USDA. 2000. Air Quality Research and Technology Transfer White Paper and Recommendations for Concentrated Animal Feeding Operations. Report by Confined Livestock Air Quality Subcommittee of the USDA Agricultural Air Quality Task Force, Washington, D.C., July 19.
Van Horne, P.L.M., J. Brake and C.M. Williams. 1998. Economics of controlling ammonia emission from commercial laying farms. Applied Poultry Science 7:61-68.
Table 1. Emission abatement techniques for livestock facilities and their target pollutants.
Table 1. Continued.