Overview of Methods to Reduce Odorant Emissions from Confinement Swine Buildings

Transcription

1 Overview of Methods to Reduce Odorant Emissions from Confinement Swine Buildings Gerald L. Riskowski, P.E. Professor and Head Biological & Agricultural Engineering Department Texas A&M University INTRODUCTION Odors are emitted from a variety of sources in swine production facilities. A large quantity of odorants can be emitted from manure handling and storage facilities. However, swine production buildings can also emit significant levels of odorants. This is especially true if manure is held within the buildings for periods exceeding 4-5 days. Manure also sticks to floors, walls, equipment, and pigs. Feed is often spilled in areas where pigs don t clean it up. This manure and feed can be around for several days or weeks and release highly objectionable odorants if these organic materials break down under anaerobic conditions. The amount of surface area of these odorant sources can be large and lead to high emissions of odorous gases. To further complicate matters, swine buildings usually have high concentrations of dust in the air and odorants adhere to the dust so the dust can also carry odors out of the buildings (Hoff et al., 1997a). Hundreds of different gaseous substances are produced within swine buildings. Fortunately, most of these substances are not odorants and do not produce a negative response from most people who smell them. The most important constituents of objectionable odor from the breakdown of organic material in swine facilities appear to be indole, p-cresol, phenol, skatole, volatile organic acids (acetic, propionic, isobutyric, butyric, isovaleric, valeric, caproic, and heptanoic), and ammonia. The level of swine odor is not closely related to the levels of ammonia or hydrogen sulfide in the air (Sweeten et al., 2001). A fairly authentic swine odor can be created artificially in the laboratory by combining fewer than 20 substances in the right proportions (DeSpirito et al., 1999). Many of these same substances can be combined in different proportions to create very different aromas, so the presence of a particular group of substances does not necessarily mean that there will be a specific odor response in humans. The odor detection concentration for humans is very low for many of these substances, so they have to be diluted to very low concentrations before the sensation disappears. Swine buildings also have significant levels of airborne dust. Most of these particles are organic (80-90% feed, 2-8% manure, 2-12% from the pigs) but are not highly odorous by themselves. However, gaseous odorants in the air will readily adsorb onto the particles and will be re-emitted from the particles for relatively long periods after the particles leave the swine building. Although, the amount of odorants on the particle may be small relative to the gaseous quantities, particles behave very differently in the air than do gases and can have very different odor transport characteristics relative to gaseous odorants. Once air from swine buildings is exhausted 122

2 to the outside, the gaseous odorants will be diluted to undetectable levels relatively quickly under most Illinois weather conditions. However, dust particles do not disperse as readily and each particle can carry concentrated amounts of odorants on their surface for relatively long periods. If you also consider that human response to these odorants varies widely among people, it is easy to see why odor measurement and control is a complicated subject. Unfortunately, people are very sensitive to these odors and you may need to reduce the odor emissions substantially before the odor levels become acceptable at locations immediately adjacent to the swine buildings. Probably, the best strategy is to reduce emissions of odorants sufficiently so they will dilute to more acceptable levels at a shorter distance from the facilities. There is usually a cost to implement and maintain management and technological means of reducing odor emissions. The amount of investment that a producer may wish to make in odor control will vary considerably with their circumstances. Odorants are emitted from a number of sources in swine production facilities (Miner, 1995). Consequently, odor control will usually require the application of several control strategies at once so all the major sources can be addressed. Each facility needs to be analyzed systematically and all the appropriate odor control strategies applied to counter each of the large odorant sources in that facility. The odor reduction technologies applied must be compatible with the management capabilities at the facility. Technologies or methodologies that exceed management capabilities will be poorly managed or eventually abandoned. There are several strategies that have been be applied to reduce odor emissions from swine facilities, and I will discuss some in the following text. Separation Distance Odorous gases and dust dilute to lower concentrations as the odorous air moves and mixes with the surrounding air. The more distance between the swine facilities and people s homes, the greater the opportunities for dilution and the lower the odor perception. If building exhaust air can be mixed with more surrounding air, then it will dilute odors. Some swine producers have planted trees or installed other obstructions such as large walls between the swine facilities and neighbors in hopes of getting more air mixing (Bottcher, et al., 2000). Other industries exhaust contaminated air from high stacks or chimneys to get better mixing of the contaminated air with clean air before it moves back down to the earth s surface. Computer modeling by Williams (2003) has indicated that the exhaust may need to be 5-10 m up before it does much good. Odors move primarily with the wind, but can flow down land slopes (air drainage) as air is cooled during the night. It is best to locate swine facilities where prevailing winds and air drainage downhill on calm nights will not carry odors to neighbors. Shield swine production units from the view of the general public. Keep the facilities clean, neat and in good repair to present a good image. Maintaining good relationships with the neighbors helps reduce conflicts. 123

3 Reduce Emission of Odorants at the Source It is typically much easier to control odorant emissions at the source than to try to remove them from the air after they have volatilized. Removing low concentrations of specific gases from the large quantities of air that move through swine buildings is a daunting task. Strategies for reducing emissions at the source include removing the source from the building, diet modification, manure additives, coating or covering the source, and reducing the surface area of the source exposed to the air. Building and Environmental Factors Miller et al. (2003) studied 26 swine production buildings on 10 farms and related a number of factors to odor levels being emitted from the building. This study measured the increase in odor level as air moved through the buildings from the air inlets to the fan exhausts. Following is a summary of some of the relationships found in this study. Temperature and humidity As temperature and relative humidity increased, odor level decreased. This could be at least partially related to the higher ventilations rates that occur as temperatures increase. Pig density Fewer pigs per unit floor area reduced odor levels. Pig health When pig health was good, odor levels increased. Air cleanliness Buildings with cleaner air had lower odor levels. Pit depth If pits were deep (greater than four feet) and had a three feet depth of manure or less, then odor levels were reduced. Cleaning Facilities A simple and relatively low cost method of reducing the amount of odor source that is exposed to the air is regular and thorough cleaning of all surfaces that may have exposed manure. This includes the pigs themselves since they often have manure on their hair and skin. Manure should be removed from the building often every 3-4 days. Studies have shown that odorous sulfur compound emissions from swine buildings increase quickly 4-5 days after the last cleaning and substantially drop immediately after the building is cleaned and manure removed from gutters. One of the most effective odor control methods is to remove all manure from the buildings often and store in covered outside tanks. The building should be designed specifically to make it easy to clean. Smooth surfaces, good manure handling facilities, and easy worker access to all areas for cleaning will help this process. A study was conducted at the University of Illinois on the effect of room washing on reduction of gases, dust and odor in swine buildings. The treatment room was washed daily with a commercial power washing machine to wash the pens, fences, floors, and walls up to a height of 4 feet. The daily washing resulted in a reduction in ammonia, odor intensity, and sulfur based volatile organic compounds in the air. However, dust concentrations were not clearly influenced by daily room washing. Pig growth performance was negatively affected by the daily washing. Although washing rooms on a daily basis in large facilities is not considered to be practical, it does show that there may be some potential of odor reduction by keeping surfaces clean. On the 124

4 other hand, Miller et al. (2003) found that as building cleanliness improved, odor levels increased. The key is reducing the surface area exposed to the air of organic material undergoing anaerobic decomposition. The amount of dry manure exposed to the air may have relatively little influence on odor levels. Sprinkling Small Amounts of Oil Studies have shown that sprinkling a small amount of vegetable oil on floor and pen surfaces, and on the pigs can significantly reduce dust levels (50-80% dust mass reductions) in swine buildings. Claims have been made that it also reduces the emissions of odorous compounds into the air. It is generally believed to reduce health problems in workers and animals, primarily because of the dust reduction. A recent study at the University of Illinois showed that oil sprinkling reduced dust concentrations by over 50% without any detrimental effects on pig performance (Anderson, 2002). It is important that the oil be applied at low pressure to form relatively large droplets that fall from the air onto the surfaces. If the oil is applied at high pressure, it tends to form a fine mist that gets into the worker s and animal s respiratory systems. Midwest Plan Service (MWPS, 1997) recommends sprinkling 40 ml/m 2 of floor for the first two days; 20 ml/m 2 the second two days, and 5 ml/m 2 for the rest of the time the pigs are in the building. Smaller facilities could apply the oil with a hand sprayer. Automatic oil sprinkling systems are being developed for larger facilities but many oils tend to transform into a gum which plugs sprinklers. Removal of Gaseous Odorants from Air Dust Removal Since odorous compounds can adhere to dust particles, it is conceivable that odor levels could be reduced by removing dust. In fact, some industrial processes use a dry scrubbing method where particles are added to the air to adsorb chemicals in the air, then the dust is removed which also removes the chemicals. Most swine buildings already have high concentrations of dust in the air that should be capable of adsorbing significant amounts of odor. Removing dust from the air is a challenge because the high concentrations quickly clog dust filters and the small dust sizes are difficult to capture by existing commercial centrifugal cleaners. An aerodynamic deduster has been developed with the help of C-FAR funding, which can remove many of the small particles with little pressure drop across the unit, and it requires little maintenance. Two dedusters were attached to an air recirculation system in a swine building and reduced dust mass concentrations in the air up to 50%. Odor levels were not measured. Wet scrubbers have also been developed for removing dust from the air of ventilation fans before it is exhausted to the atmosphere. To be practical, these units would need to have little restriction on airflow and would need a system for cleaning the water so it can be recycled. A unit developed at the University of Illinois, reduced fan performance less than 1.5% and removed around 80% of dust mass from the air. The water also adsorbs water soluble compounds form the air and the wet scrubber was found to remove 1/3 to 2/3 of the total volatile organic compounds from the air depending on the amount of water used and the contact time allowed between the water and air. 125

5 The reported amounts of odor reduction due to dust removal vary widely in the literature (~0% to over 90% reductions). Dr. Steve Hoff and colleagues at Iowa State University tested various biomass air filters made from field residue on the ventilation exhaust of a swine nursery building and found significant dust and odor reductions (Hoff et al., 1997b). Dust removal varied between 45 and 75% with subsequent odor threshold levels dropping by 50-90% between inlet and outlet of the filter. Zhao et al. (2001) found only an 8% reduction in odor intensity with a wet scrubber that removed around 84% of the dust. There are, no doubt, a number of contributing factors that are not being accounted for across these studies. Many of the odor-measuring methodologies filter out particles in order to reduce complications in the process, so they may or may not account for the contribution of particles in the first place. This could confound the effort to determine the effect of dust removal on reductions of odor perception. The amount of dust initially in the air of the swine building will also have a large effect. Removing 80% of low quantities of dust from the air will have less impact on odorant levels in the air than removing 80% of large quantities of dust, because larger amounts of dust will adsorb larger amounts of odorants. Another possible problem for wet scrubbers is that some of the odorants may react with the water to produce other odorants. For example, acetic acid, a prevalent organic acid in swine odor can react with water to be transformed to ammonium acetate which is another odorous compound. Williams and Muggli (2001) suggest that the addition of common baking soda (sodium bicarbonate) to the water may help alleviate this reaction. Biofilters Biofilters can work well for removing odors and dust from the ventilation fan exhausts if properly designed and maintained (Nicolai and Janni, 2000). They have been used extensively for removing a number of compounds from air in industrial processes. Biofilters provide moist material with a great deal of surface area on which micro-organisms can grow. Air moves through the biofilter and odorants are adsorbed onto the material which allows the microorganisms to degrade odorants to less odorous compounds. Biofilters can be constructed at a relatively low initial cost as has been demonstrated by the University of Minnesota. Their biggest problem is the large pressure drop across the biofilter media, which leads to high operating costs for high airflows. They are used mainly for low airflows that occur during cold weather ventilation of swine facilities. They are also difficult to manage since the media needs a continuous supply of moisture, heat, and energy source for the bacteria populations to thrive. They can be made to work well for the continuously operating cold weather fans, but the intermittent operation of the temperature control fans are a problem. Consequently, biofilters have been used in a very limited number of special applications. Ozone Ozone is a very reactive compound that is believed to reduce odor by breaking down many odorous compounds in the air. Ozone can be dangerous at certain concentrations because it can irritate the respiratory system. Most recommendations are that ozone levels not exceed 0.1 parts per million (ppm) in the air for humans. It is not known what levels are acceptable for pigs but the same limit is usually used in swine buildings because of the human workers. North Carolina 126

6 State University (Keener, et al., 1999) and the University of Illinois (Elenbaas-Thomas, et al., 2003) have studied ozonation of swine building air and the results are mixed. The North Carolina study found a reduction of ammonia and better pig performance with ozone. The Illinois study found that ozone application at the maximum concentration of 0.1 ppm did not have any statistically significant effect on bacterial count, dust mass concentration, ammonia concentration, hydrogen sulfide concentration, odor intensity, and sulfur compound concentration. Nor did it have any statistically significant effect on pig growth performance in terms of average daily gain and feed efficiency. It is believed that the ozone reduces some of the odorous compounds but has little effect on others. Consequently, the characteristics of the odor may change but there is still a lot of odor being emitted. For example, the Illinois study found that sulfur compounds are not affected by ozone, but some of the other volatile organic compounds were reduced. Higher concentrations of ozone may have more of an effect on odor levels but health issues will limit this application. The University of Minnesota has tested the odor reduction potential of non-thermal plasmas that are also highly reactive with odorous compounds (Goodrich et al., 1999). Catalytic Methods Catalytic converters have been used for years for removing undesirable gases from car exhausts. They consist of a catalytic material that adsorbs gaseous molecules which are then slowly oxidized to harmless compounds. The type of catalytic material is selected based on the molecules that you want removed. Drs. Masel and Wiltkowski tested a copper catalyst for removing acetic acid from air. The tests showed good reductions if the airflow is carefully matched to the amount of catalytic material. High static pressures from moving air through the catalytic material will increase energy costs. REFERENCES: Anderson, B.K Managerial and nutritional manipulation to reduce swine odor. Unpublised Ph.D. Thesis, University of Illinois at Urbana-Champaign. Bottcher, R.W., K.M. Keener, and R.D. Munilla Comparison of odor control mechanisms for wet pad scrubbing, indoor ozonation, windbreak walls, and biofilters. Paper No ASAE International Meeting, Milwaukee, WI, ASAE, St. Joseph, MI. DeSpirito, A.A., J.A. Zahn, D.W. Russell, E.E. Cooper, and J.L. Hatfield Development of a standardized method for odor quantification from livestock wastes: Development of an odor index. Final report to the National Pork Producers Council. Goodrich, P.R., Y. Wang, H. Ma, S. Deng, and R.R. Ruan Odor destruction using a barrier discharge reactor. Paper No , ASAE/CASE International Meeting, Toronto. American Society of Agricultural Engineers, St. Joseph, MI. 9 p. Hoff, S.J., D.S. Bundy and X.W. Li. 1997a. Dust effects on odor and odor compounds. Proceedings of the International Symposium on Ammonia and Odour Control from Animal Production Facilities. Vinkeloord, The Netherlands, October pp

7 Hoff, S.J., L. Dong, X.W. Li, D.S. Bundy, J.D. Harmon, and H. Xin. 1997b. Odor removal using biomass filters. Proceedings of the 5 th International Livestock Environment Symposium. ASAE, St. Joseph, MI. pp Keener, K.M., R.W. Bottcher, R.D. Munilla, K.E. Parbst, and G.L. VanWicklen Field evaluation of an indoor ozonation system fro odor control. Paper No , ASAE/CSAE International Meeting, Toronto. American Society of Agricultural Engineers, St. Joseph, MI. Miller, G.Y., R.G. Maghirang, G.L. Riskowski, A.J. Heber, M.J. Robert, and M. Muyot Management and other factors that influence air quality and odor. University of Illinois Pork Industry Conference on Swine Odor and Manure Management. Champaign, IL. Miner, J.R A review of the Literature on the Nature and Control of Odors from Pork Production Facilities. The National Pork Producers Council, Des Moines, IA. MWPS Sprinkling oil to remove dust, odor, and gases in swine buildings-aed 42. Midwest Plan Service, Ames, IA. Nicolai, R.E. and K.A. Janni Designing biofilters for livestock facilities. Proceedings of the 2 nd International Conference on Air Pollution from Animal Operations. Des Moines, IA. p Sweeten, J.M., L.D. Jacobson, A.J. Heber, D. R. Schmidt, J.C. Lorimor, P.W. Westerman, J.R. Miner, R. H. Zhang, C.M. Williams, and B.W. Auverman Odor mitigation for concentrated animal feeding operations. White Papers for the National Center for Manure & Animal Waste Management, Midwest Plan Service, Ames, IA. Elenbaas-Thomas, A.M., L.Y. Zhao, Y. Hyun, B. Anderson, G.L. Riskowski, M. Ellis, and A.J. Heber Effects of Ozonation on Gas, Dust, Bacteria Levels and Swine Growth Performance. Submitted to Transactions of the ASAE. Williams, A. and J. Muggli Atmospheric dispersion of swine odor from confinement buildings and lagoons: preliminary results. Five Year Progress Report to the Illinois Council on Food and Agricultural Research (C-FAR). Williams, A Dispersion modeling of hog-odor transport. University of Illinois Pork Industry Conference on Swine Odor and Manure Management. Champaign, IL. Zhao, L.Y., G.L. Riskowski, P. Stroot, M. Robert, and A.J. Heber Development of a wet scrubber to reduce dust and gaseous emissions from swine buildings. Paper No ASAE International Meeting, Sacramento, CA, ASAE, St. Joseph, MI. 128