A Review of the Literature on the Nature and Control

of Odors from Pork Production Facilities

Executive Summary
The Olfactory Process
Psychological Response
Odor Intensity Measurements
Regulatory Efforts to Control Odors
Climatology and Odor Transport
Odor Sources Associated with Pig Production
Application of Manure to Cropland
Feed Additives to Reduce Odor
Air Treatment Alternatives
Producer Options
The Future

Research has demonstrated odor has at least two aspects. One, the objective portion, is measurable both in concentration and duration. The other, more subjective aspect, is that of offensiveness. How good or bad an odor is is related to individual preference and previous experience. Observations over the past twenty years suggest people who are less acquainted with pig production odors, who have another interest in not smelling the swine odor, or have some other basis for their negative feelings toward a swine operation, are generally more likely to complain of pig production odors. People who see the pork industry as a contributing component of the local economy are generally more tolerant.

Technologies exist to produce pigs with a degree of odor control that is judged to be acceptable. The changes are related to the cost of systems that provide a high degree of odor control compared to those systems that do not. The situation is further complicated in that not all locations require the same degree of odor control nor are the requirements stable with respect to time. Larger operations have a larger odor production potential and may find the technologies appropriate for small operations are not acceptable for their use.

Two manure management schemes predominate in pork production facilities at this time. One is the storage of manure as a slurry in one or more pits or tanks immediately beneath the confinement facility or in a tank located outside the facility. The goal is to transfer the manure into the storage facility with a minimal dilution of water. There is a continual odor release at the time of agitation in preparation for field application. One odor control alternative is to cover the manure in storage. The cover may be an impermeable cover such as that involved in an anaerobic digester for the production of biogas or a permeable cover designed to biologically oxidize the odorous gases as they pass through the covering material.

A second popular manure management system includes the incorporation of an anaerobic lagoon. Lagoons provide a low cost means of manure storage and result in a large portion of the nitrogen originally in the manure escaping to the overlying air. Proper lagoon design and management are intended to achieve a relatively low intensity of odor release. This approach is effective most of the time, however, during the late spring as water temperatures increase, elevated odor levels are more frequent. As lagoons become larger, the odor releasing surface becomes sufficiently large enough to present an odor control problem.
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Odor perception begins well up in the nasal cavity where we humans are outfitted with a collection of highly specialized receptor cells. As individual odorous molecules are drawn into the nasal cavity, a portion are dissolved in the mucous film that covers these specialized detectors. Once an odorous molecule is captured in the system, it will become attached to one or more of the individual receptor cells based on a shape match. Depending upon the molecule, it may be captured by one or several of the specifically shaped receptors. Once a receptor has been stimulated, an electrical signal is transmitted to the brain and an amazing process is underway.

Once a signal is generated, the brain takes over and we respond. The reaction may be to flee because of an association with danger or it may be to linger because of the perceived desirable situation. Some writers have asserted that human beings can detect over ten thousand different odors even though we can identify only a small percentage of these. The sense of smell is much more precise than is our ability to describe the odor we have perceived.
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The psychological response to odors is more complex and less well understood than the physiology which has been extensively explored during the past thirty years. Evidence suggests that each of us learns to like or dislike certain odors. Children like almost all smells. It is only as we mature and begin to talk about the odors that we develop a sense of likes and dislikes. Food tastes are very much related to the odors from those foods. Subtle spicing would be ineffective except for the multitude of differences we can detect.

Only recently have scientists begun to relate these complex psychological reactions to the ways in which people respond to specific odor sources such as those associated with pork production. Clearly, individuals react differently to the smell of any particular odor source. There are experiences of people who react to swine lagoon odors with an emotional intensity that others would find entirely unreasonable. Recent observations suggest these are honest and accurate reactions. Whether these responses are so intense because they have an objection to the odor source based on other factors is unclear at this point. It has been observed, however, that there are fewer objections within a community to those odors that are a traditional part of the community, or are produced by an agricultural operation of an appreciated and esteemed member of the community, than to an odor generated by an outside agent's operation that may alter the traditional social structure. Thus, a large high tech swine confinement system relocating to an area of traditional style pork production can expect to have the local residents find the odor more objectionable than an odor of similar intensity from a more conventional system of pork production.
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Odor intensity is usually considered one of the primary factors in deciding whether a problem exists. Several methods of assessing odor intensity have been proposed and used. The most obvious method is the direct scaling technique. This approach involves asking a panelist or other unbiased observer to evaluate an odor intensity on a numerical scale. Some researchers have proposed scales of one to six, others have used one to ten with the higher numbers representing the more intense odors. This technique was used as long as sixty years ago. A modification of this technique which improved its usefulness was to also provide the panelist with a standard of defined magnitude. This tends to reduce the variability among panelists.

Referencing is an alternate technique. The panelist is asked to compare the intensity of an unknown odor with a series of different concentrations of a reference odorant. The panelist indicates whether the odorant being evaluated is more, less, or of the same intensity as a particular standard. The most common standard is 1-butanol because of its being available in a highly purified form, low toxicity, high stability, and its reasonably agreeable odor. Olfactometers based on 1-butanol have been constructed by odor researchers for the past 25 years. More recently, portable units have been made and techniques have been perfected for bringing odorous air samples into the testing site. Exposing fabric swatches to odor sources and then comparing those swatches has been proposed as an alternative to either transporting the odorous air to panelists or to transporting panelists to an odor source.

Dilution, either liquid or vapor, has been used as an approach to evaluate odor intensity. Although several techniques have been used, all are similar in concept. Panelists are presented samples of diluted odors to determine the dilution of the odor they can barely distinguish from an odorless sample. Both liquid and gas comparisons have been conducted. The equipment for these comparisons range from the relatively simple to the highly complex. The Scentometer, a commercially manufactured device, can be taken to the field and diluted samples of the ambient air compared to an odor free air. Scentometer evaluations of odor intensity have been widely used because of the low cost and convenience of the tool. More precise dilution olfactometers are in widespread use for research purposes. The devices are all similar in that they deliver diluted samples of odorous air to panelists for comparison to an established standard.

An indirect approach to measuring odor intensity has been to measure the concentration of a constituent that is present in the odorous air and is easily measured. This approach has particular appeal if the constituent being measured is a major contributor to the odor being represented. Ammonia and hydrogen sulfide have been the two constituents most commonly measured in regard to manure odors. Although most researchers seem to agree that neither is the major constituent of swine manure odors, their removal or reduction in concentration has generally been used as an acceptable surrogate for odor removal. Volatile organic acid concentrations have also been used as an alternative to odor intensity assessment and the correlation is good enough to be useful.

More recently, electronic sensors have been proposed that might have the potential for odor intensity measurement. If such a device was available it would contribute a degree of objectivity to the odor measurement process. Most detectors currently available respond to a particular constituent so they would not be appropriate for a complex odor like that from a manure lagoon. A broad range electronic detector has been manufactured and was proposed as an odor measuring device. However, initial testing at cattle feedlots and dairies was not encouraging.
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Swine odors are not regulated by federal statutes nor by the air pollution control agencies of any of the states. Many states, however, have expressed concern over the complaint they have received from citizens related to odors. Because of the complexity in defining the FIDO factors (frequency, intensity, duration, and offensiveness), regulations have been difficult to formulate and would be equally difficult to enforce. As an alternative, several states and local units of government have established regulatory guidelines concerning the construction of swine facilities that are designed to indirectly reduce odor complaints. One of the approaches is to specify the minimum required separation distances between confinement buildings and nearby residences or public gathering areas. Another has been to restrict the use of anaerobic lagoons. A third approach has been to insist on a minimum area for manure disposal to be located in close proximity to confinement systems. A fourth approach has been to insist on adoption of best available control technology (locally defined) as a condition to issuance of a construction permit.

Several states have adopted "Right to Farm" Legislation designed to protect agricultural pursuits from the encroachment of housing development into areas of established agriculture. The goal was to avoid lawsuits that were resulting from having persons unfamiliar with agricultural odors attempting to halt or change established agricultural practices because of their having moved into the area. The provision of the various "Right to Farm" laws are different and the protected practices vary from one state to another. Most protect the opportunity to spread manure on cropland. Others provide an establishment time. Any agricultural practice that has been continuing for that time or longer is protected from the arrival of new residents or the development of new concerns by existing neighbors.

The most frequent threat to swine producers relative to odors are the private or public nuisance suits that have been filed at various locations around the country. Nuisance litigation is based on the concept that no one has the right to unreasonably interfere with another's right to enjoy his/her property. When present at unreasonable concentrations or for unreasonable times, odors have been considered sufficiently important to have been judged a nuisance on several occasions. Each case must be considered separately and the judge/jury generally evaluates each location separately in deciding what can be considered an unreasonable odor level. Where a nuisance has been judged to exist, damages may be assessed against the odor source. Damages may be actual for medical costs, alternate housing, or for more frequent cleaning of furniture or draperies. Punitive damages may also be assessed where it is decided that some additional payment is in order because the odors were caused by negligence and irresponsible actions. Nuisance lawsuits have been heard in almost all of the major livestock producing states and have proven to be an expensive alternative for those producers who have become directly involved.
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Odors released into the environment are transported by wind and subsequently diluted by atmospheric turbulence. Turbulence increases with greater wind velocities and with the presence of surface roughness such as hedges, trees, and buildings. Incoming solar energy warms the earth surface. Some of that absorbed heat is transmitted to the air, which expands as it warms, creating an upward buoyancy. This unstable condition contributes to the normal process whereby odors are dissipated in the environment. The Gaussian plume dispersion equation has been adopted as the most common starting point in attempts to predict the extent and concentration of downwind odor concentrations. This highly theoretical model has the advantage of being amenable to mathematical solution, but in exchange it ignores many of the local topographical features that are important in understanding odor transport.

Both modeling and practical experience have taught that the most intense odor concentrations occur under highly stable atmospheric conditions known as temperature inversions. Temperature inversions occur when the air temperature increases with height. Such a ground inversion can be noted on a clear wind-free night when there is rapid cooling of the earth's surface. As wind speed increases, typically in the morning, mechanical turbulence begins to dominate the odor transport process.

The combination of air velocity and temperature changes can cause some unexpected odor transport results. For example, during a clear night of low wind velocity, cold air can flow down a hill and fill a valley causing odors to dissipate much more slowly than would otherwise be expected.

Models based on the Gaussian plume calculations to predict the movement and dispersion of animal waste related odors have been used in the Netherlands and are sometimes required in Australia. They have not been applied to the siting of livestock facilities in the United States because of the problems inherent in the process. Standard Gaussian plume models are not designed to simulate atmospheric pollutant transport over rough terrain or around objects, nor do they account for vegetation effects.
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Odorous gases can be produced at a number of sites around a livestock enterprise. The most common odor sources, however, are the floor and other surfaces of buildings and pens, the surfaces of animals, the manure collection and storage facilities, feed storage facilities, dead animal disposal and storage areas, and manure exposed to the air during land application. Each of these odor sources has received research attention, and technologies exist that can be employed in response to the issue. One of the unresolved issues is the matter of the need for odor control and the associated question of the willingness and capability of pig producers to invest in odor control. Certain odors have historically been associated with pig production and were regarded as "normal." Pork producers accepted these as part of their environment. As pork production technology has changed, pork producing enterprises have grown in size, and as rural residents have become less tolerant of invading odors from nearby pork production operations, the need to address the odor management questions has become more acute.

Odors from the floor, pen partitions and the bodies of confined animals have been a serious issue that has been reduced as designers have become better informed about how to design buildings that promote clean animals and clean pens. The use of slotted floors and flushing gutters have simplified the separation of manure from animals. Early confinement buildings reflected a limited understanding of swine physiology and ventilation needs. As a result, dirty, manure-covered animals were not uncommon. Animals were forced to roll in manure as a source of cooling. Dirty animals were a particular problem both because of the additional area of manure-covered surface, and because the animal body was a warm surface. Conventional building design assures that animals are maintained at a comfortable temperature and that the design of the pen provides an opportunity for pigs to remain clean, dry and manure-free. Misting equipment has been added to buildings in warm climates to provide helpful evaporative cooling to animals. By minimizing the amount of manure on pen floors and along partitions, the amount of odorous gas is reduced. Clean animals and pens can be achieved in a variety of ways. The use of properly ventilated pens, appropriate animal stocking densities, and either partially or fully slotted floors will achieve the desired result. Aa an alternative, open gutter systems have been equally successful.

The manure collection, storage, treatment, and transport system has been the focus of odor control research because of the earlier observation that this is the odor source of greatest importance to downwind neighbors. Storage of manure both underfloor and outside the building storage structures is being widely used. The underfloor storage tanks are generally designed for a minimum of water addition to extend the storage capability. Most underfloor storages are allowed to stand quiescent. One exception has been the use of underfloor oxidation ditches which were popular during the seventies. With adequate mechanical aeration, the storages could be maintained at markedly reduced odor levels. In addition, much of the nitrogen was lost by alternate nitrification - denitrification. Although the process improved the quality of the building environment, energy costs were sufficient to make this alternative less attractive by the eighties. The more common approach to underfloor storages has been to install a portion of the exhaust ventilation capacity above the manure level and below the slotted floor to reduce the upward movement of odorous gases.

More typically, swine manure is being removed from the building for storage and/or treatment. Alternatives for manure removal include a variety of scraping devices that operate in shallow gutters, flushed gutters that are located beneath slotted floors or are open to the animals, and short term storage pits that are partially filled with water and dumped on a regular basis (so-called pit drain systems). The scraping devices involve considerable mechanical maintenance and have been blamed for elevated building odor levels because of the residual manure that is left. Both open and underfloor flushed gutters offer the possibility of removing manure on a daily or more frequent basis, the use of recycled effluent as flush water, and a system that is easily automated. The fill and dump pits are also easily adapted to the use of recycled water and have the possible advantage that the manure is continuously covered with water. By being covered with water, there is less odor generating surface exposed to the air.

Exterior manure storages may be either above or below ground. The below ground manure storages may be in a water tight tank made of concrete or some other impervious material. That tank may be partially covered to reduce the rate of air exchange between the manure and the ambient air. Alternatively it may be open. Safety is a critically important aspect of manure storage tank design. All manure storage tanks should have safety guards that prevent accidentally falling into the tank. Most manure storage tanks are designed to operate with a minimal addition of water. The tanks are generally not agitated until immediately prior to emptying. Agitating a previously quiescent tank of manure will release a large quantity of potentially lethal gases. Pork producers should protect themselves, their families, their employees and livestock from both suffocation and gas toxicity. They should not stand over or adjacent to manure storage tanks as they begin to agitate. Odor problems from underground manure storages can be reduced by keeping the tanks covered. Most odor complaints occur when the tanks are agitated or being emptied. If manure is being loaded into a trailer or truck mounted tank, agitation and splashing can be minimized by proper equipment selection and placement.

A second popular manure management system includes the incorporation of an anaerobic lagoon. Lagoons provide a low cost means of manure storage and treatment. They provide an opportunity for anaerobic bacteria to convert manure volatile solids into liquids and gases such as methane and carbon dioxide. Lagoons result in a large portion of the nitrogen originally in the manure escaping to the overlying air. Proper lagoon design and management are intended to achieve a relatively low intensity odor release. This approach is effective most of the time; however, during the late spring as water temperatures increase, elevated odor levels are more frequent. As lagoons become larger, the odor releasing surface becomes sufficiently large as to present an odor control problem to a larger area and potentially a greater number of people. Odor concerns around anaerobic lagoons include the ongoing escape of odors from the surface and the more extensive escape at the time of removing liquid if it is applied to land using conventional irrigation equipment.

One alternative for odor control around an anaerobic lagoon is to lower the loading rate, increasing the volume of lagoon relative to the organic loading. Lagoon loading rates are typically expressed as lagoon volume per pound liveweight of animal served. Recommended volumes range from 1.5 to 3.0 cubic feet per pound of pig being served depending upon location. Lagoons in the southern part of the U.S. can be smaller because of the warmer temperatures. Overloaded lagoons, those with less than the suggested volume, are generally considered as being more odorous. In quest of odor reduction and operational efficiency, the American Society of Agricultural Engineers has adopted a standard design practice for anaerobic lagoons that incorporates low volatile solids loading rates and necessary storage of liquids and solids.

Chemical and biological additives, masking agents, and other products have been proposed and are commercially available for use in lagoons or manure storage systems. Typically, they are proposed to improve lagoon performance, liquify the accumulated solids and reduce odors. There is little supporting data, however, to document the success of these materials. There is generally no shortage of well acclimated bacteria in the lagoon nor is there a problem with low pH in a properly designed and well operated lagoon.

In addition to an adequately sized primary anaerobic lagoon, a lightly loaded second stage lagoon is often included that will provide further treatment and storage of effluent. This will usually result in effluent of lower odor potential for irrigation and recycling as flush water.

Two types of lagoon covers have also been proposed. Impervious covers, rubber or plastic material, have been installed on several industrial waste anaerobic lagoons, slaughter houses, packing plants and food processors. The captured gases can be burned or can be deodorized by venting into a soil bed. Impervious covers have proven effective in reducing the odor of lagoons but have not been widely adopted by pork producers because of the cost involved. Researchers have noted that when floating scums develop on dairy manure lagoons, the odor release is reduced. An experimental floating permeable cover has been proposed but is not currently available as a commercial product.

Aeration is an alternative that is available to designers of lagoons and other storage units. By the addition of mechanical aerators, the anaerobic process can be converted into an aerobic one with the associated odor control benefits. Most often, when an aeration process is selected, a portion of the organic loading is removed by some other process, either sedimentation or screening to separate the solids, or anaerobic decomposition in an enclosed environment. Thus, one potential manure handling system would include a solid liquid separator followed by an aerated storage lagoon. Another option would be a covered anaerobic lagoon followed by an aerated lagoon.

Anaerobic decomposition with biogas recovery has been practiced in much of the world as a way to reduce the land area required for manure management and reduce odor release, and to claim a portion of the energy as a biogas fuel or as locally generated electrical energy. These systems are widely used in Asia but have had little appeal in the U.S. because of the higher operating costs and the greater initial investment. The technology is available for the construction of manure handling equipment of this type.
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Land application is the final step in most swine manure handling schemes. This step is a frequent cause of odor complaints because it creates a large surface area from which volatile compounds can escape. The most frequent response to this concern is to modify the application procedure to accommodate neighbors. Frequently, complaints can be avoided by selecting a time to haul manure when the wind will blow odors away from the sensitive areas. Application of manure in the early part of the day when there will be better drying conditions will also help. Obviously, it is thoughtful to avoid spreading manure immediately prior to a holiday or weekend when you might expect neighbors to be planning outdoor entertainment. Prompt incorporation of the spread manure into cropland will also help in avoiding odors. Soil injection is the most effective way to reduce the escape of odor during land application. Soil injection is also helpful in reducing ammonia loss.

Application of lagoon contents is a necessity to maintain a stable chemical balance in the lagoon system with respect to salinity and ammonia. One method, irrigation, is particularly prone to odor release and complaints triggered by visibility as well a odor detection. Irrigation equipment will be helpful in reducing the time required for application but will require considerable management attention to avoid creating problems. Low pressure sprinkle systems create less air water contact than high pressure systems. Irrigation from lightly loaded well managed, anaerobic lagoons and from second stage or tertiary lagoons will provide effluent of higher quality and less odor.
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There have been several attempts to reduce manure handling odors by altering the ration being fed or by the addition of specific odor reducing material, such as sagebrush, mint oil and a sarsaponin extract of the yucca plant. Although the data from these materials are not conclusive, they suggest that it is possible to alter the odor of fresh manure; however, that change does not persist once the manure undergoes anaerobic storage.

A related approach to manure odor control is to alter the feeding regime to achieve enhanced nutrient utilization. This approach has a logical attractiveness in that if the amount of manure could be reduced, there would be a reduced potential for the formation of odorous compounds. The use of synthetic amino acids is being investigated and has been reported to result in reduced nitrogen in the feces and urine. At this point, the research is still in a preliminary stage and does not offer a clear possibility to the pork producer as a technique to reduce his exposure to potential odor problems.

Even less developed at this time is the possibility of manipulating the microbiological populations in the digestive tract to enhance animal performance and minimize nutrient excretion. This approach has potential triple benefit in reducing feed costs, manure handling, and the need for antibiotics to control disease organisms.
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Various means to reduce the odor of air have been employed in those industries with long term odor concerns. Absorption and adsorption processes have the potential to remove many of the chemical compounds identified in swine building exhaust. Activated carbon adsorption is widely used in these industries but has obvious limitations when considered for livestock enterprises because of the large volume of air that is typically handled. European researchers have, however, used water based scrubbing units to capture ammonia from the air within a swine building.

An alternative to this technology that has been utilized in the rendering, livestock, and poultry industries has been to pass odorous air through a shallow soil absorption bed. In this process a unit similar to a septic tank absorption bed was constructed into which the exhaust air was discharged. By having the bed relatively large, the headloss was reasonable and by passing the air upward through the soil layer, odor removal was achieved.
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Research is generally long on data and short on practical conclusions. If a review of the odor control literature is to be of benefit to the pork producers in this country and elsewhere, it must have some practical conclusions.

Odors from the decomposition of swine manure disturb nearby residents more than most pork producers anticipate. The exact reasons for why people without swine are bothered so much more than those owning swine is a bit of a mystery, but the fact is that they are. As a result, odor control is important.

It is known that odors are transported by moving air and that the odorous compounds are extracted by the mucous lining in the nose. The mechanisms of how odors are detected by the nose are relatively straightforward, but that process does not explain the more emotional reactions that are common.

Although fresh swine manure has an odor, this odor is generally regarded as being much less objectionable to nearby residents than that of anaerobic decomposing manure. This means that the most important odor sources are: (a) animals and pen surfaces that become manure covered; (b) anaerobic lagoons, particularly when heavily loaded; (c) liquid manure when being applied to cropland using irrigation equipment; (d) solid manure when applied to cropland and not incorporated; and (e) spoiled feed or decomposing animals that have not been managed properly.

Alternatives are available to reduce each of the odors listed above. Properly designed pens and equipment are not manure covered nor are animals which are housed in well designed facilities. Anaerobic lagoons can be replaced with other waste storage facilities, can be aerated, can be covered, or they can be enlarged to reduce the loading rate and odor intensity. Liquid manure can be injected directly into cropland and solid manure can be plowed into the ground immediately after application. Spoiled feed and dead animal handling systems are available that can eliminate this issue.

Unfortunately, if an odor problem exists, each of the odor solutions listed above costs more than the current way manure is being handled. Research has not identified an odor control technology that costs less than doing nothing. Many producers have sought lagoon additives that would eliminate odors. Industry has tried without success to find such a product.
Atmospheric modeling can be used to evaluate downwind odor transport; however, no model has been able to provide the separation necessary to protect a confinement building that was placed too close to a neighboring resident.
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Odor control is of increasing concern as pork production moves into ever larger units and the surrounding residents have a less direct relationship to animal agriculture. Conventional systems have devoted little direct investment to the control of odors. The future clearly demands that our systems become more effective in these matters. Additional research in this area is obviously important, but in the immediate future, application of those technologies available will be required to a greater extent. Aerobic systems and enclosed anaerobic breakdown of manure have obvious application. The use of enclosed manure storages and direct soil injection is possible in many locations where it is only marginally practiced at this time.

Of paramount importance to the success of present day systems is to avoid overly optimistic assumptions in assessing manure production and treatment efficiencies in the design of storage, treatment and land disposal systems. Overly optimistic design assumptions in these areas have frequently been utilized to justify placing an operation on a particular parcel of land that is in reality too small. These short term expediencies result in operations that are more likely to lead to either odor conflicts or to environmentally unstable systems from a nutrient management perspective. Cost saving measures in site selection and facility design can lead to cost excesses including inconvenient retrofits and neighborhood conflicts in later years.
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1. I recently received a telephone call from a person living more than two miles away from my farm. She said they could smell my pig barn. Is it reasonable to be able to detect an odor at such a large distance?

There are a number of weather conditions that can occur simultaneously and cause an odor to be transported a much greater distance than normal without the normal amount of dilution and dispersion. Temperature inversions are one of the phenomena that contribute. When an inversion occurs close to the ground it means there is a dense layer of air near the ground that has a lighter layer both above and below it. This dense layer of air effectively restricts mixing to that zone beneath the inversion layer.

A second feature that may cause odors to be transported a greater distance than normal is a low wind velocity and a lack of physical features that create turbulence. As wind velocities decrease, there is less turbulence and less dilution of escaping odors. Most odors associated with pork production are also greatest during warm weather. Warm weather promotes more rapid biological activity and greater volatility of odorous compounds. As a result, odors are generally detected at greatest distances when wind velocities are low, temperatures are high, and there is a low level temperature inversion. Under the worst possible conditions in many areas, odor transport in excess of two miles has been noted. The good news is that these conditions that promote ideal odor transport are relatively infrequent.

2. One of the neighbors who has been complaining about the odor from my farm has told a neighbor that the odor was so bad that it caused his wife to vomit. Can swine manure odors really cause people to get sick at their stomachs?

There have been a number of incidents in which people have reported being made ill by the odor of manure. Similarly, people have reported headaches, stomach cramps, and other disorders when encountering odors from a number of different sources even though there was no evidence to indicate there was anything present in the air that would have caused the owner of the farm or any of his employees to suffer similar symptoms. Thus, people are highly variable in their response to odors. These different responses come from a variety of experiences as well as some very particular differences in how we respond to specific stimulants. Some people are highly allergic to individual pollens. For others of us they are no particular problem. There is no reason to expect that all of the human bodies would respond exactly to a certain odor.

In addition to those differences that can be attributed to physiological variability, there are also differences based on our individual memories and the experiences which have shaped our lives. A person whose family raised swine and won prizes with them is almost certain to react to the smell of pork farms differently from a person who has never been around farm animals and lives under the illusion that swine are dirty and unsavory critters. Having been fired by a particular operation invariably causes the odor of that enterprise to deteriorate in quality. These may seem a trifle humorous but these are real phenomena and if we are to make a complete response to odor issues, these will be part of our understanding.

3. Does the smell of manure flow downhill?

Odors are transported by the movement of air and, strictly speaking, there is little reason to expect they will move downhill any more than uphill. However, there are a few exceptions. One exception would involve a complaint received at the time of a ground level inversion, when there was a layer of cool air beneath a warmer layer as might happen on a clear night at the top of a hill. Since there was an odor source near the top of this hill, the odorous air might, on a calm early morning hour, actually move down the hill along with the cold heavier air displacing lighter warm air. The residents of the valley were exposed to the odor at far greater concentrations than would be predicted by any of the conventional modeling techniques. The good news is that this was a most unusual situation and the valley residents did not typically experience this odor; they did on this one occasion.

4. Do odors actually cling to clothing and cause the clothing to smell long after the odor source is no longer available?

Yes, odors are quite effectively absorbed onto fabrics. Common experience supports this observation as does more controlled research. Any of us who have faced the family laundry are aware that fabrics absorb odors. Researchers have actually used freshly laundered fabrics as a way to capture odors and return a sample to the laboratory or to the home of the concerned neighbors to be certain the odor they were smelling was indeed coming from the supposed source.
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5. I have received numerous advertisements suggesting that if I purchase a certain feed additive it will reduce the odor of the lagoon. Have these materials been tested and are they effective?

There are a number of materials that can be fed to animals that will change the odor of the fresh feces and the urine. Research data, however, showed that when the manure from the test animals was stored and allowed to undergo anaerobic decomposition, the odor of the manure from those animals receiving the mint oil and sagebrush was indistinguishable from the controls.

This observation is consistent with what would be expected from a consideration of the biochemistry involved. If animals are fed a ration that meets the basic nutritional needs of the animal, it will contain about the same level of protein and energy of another ration with different ingredients. If the manure from these animals is stored under an environment that promotes their degradation to CO2 and water, about the same quantity of intermediate compounds will be formed and therefore the odors are likely to be about the same.

6. There are products on the market claiming to aid in the operation of lagoons by supplementing the enzymes and thereby reducing the odor. Have they proven effective?

A well designed anaerobic lagoon will undergo active biological action during the summer months when the water temperature is sufficiently warm. Under these conditions, there is an abundance of enzymes to moderate the decomposition process. So long as that is the case, there is no reason to expect that the addition of a relatively small quantity of a less well acclimated enzyme will have a noticeable impact on the odor being released or on the extent of biological activity underway. Controlled laboratory evaluations of these products have only recently been undertaken. Those that have been conducted to date have confirmed the projection that the addition of a small amount of additional enzyme is not likely to alter the decomposition process.

7. I have an anaerobic lagoon that in the past was not a particular problem. More recently, it seems to "stink pretty bad." This smell is worse in the late spring and early in the summer. What causes this?

If a lagoon is producing a greater odor intensity than is considered appropriate, there are some things to consider. In the first place, is the loading heavier than would be appropriate? If animal numbers have grown but lagoon size has not, this is likely the problem. One solution is to enlarge the lagoon. Another is to reduce the load. The load can be reduced by installing a solid-liquid separator or passing the manure through a settling basin ahead of the lagoon. The load can also be reduced by passing all or a portion of the waste stream through an enclosed digester and claiming some biogas.

The fact that this odor is worse in the late spring than any other time supports the theory that the loading issue becomes more critical in the late spring. During the cold winter, the lagoon was inactive due to the cooler weather and because it was cooler, the odor's changing went unnoticed. When temperatures warm up, that excess food supple is devoured by a rapidly expanding bacterial population. This is a clear prescription for elevated odors because of the bacterial imbalance. There are lots of those critters that thrive on fresh organic matter but few that are able to deal with the organic acids and other intermediates. As a result, the pH falls and the whole lagoon begins to smell like a rotten pickle jar.

8. Composting has been described as an odor free process for the natural breakdown of manure. Why have there been so few composting systems built for swine manure?

Composting is a natural aerobic biological process that has been proposed at various times to process animal manure. It is frequently seen as a way to process manure along with other waste materials such as waste paper, straw or municipal refuse. The process is a relatively simple one in which the material being composted is placed in piles and the moisture content is adjusted to about fifty percent. The moisture content is critical to allow air to completely permeate the pile. A mixed group of organisms use the organic material as an energy source and in the process leave a more stable end product that is less odorous than fresh manure and more easily handled for application as a soil amendment.

The process is a workable one. The problems are that having a relatively dry manure with which to start is not compatible with current liquid manure systems.
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9. My anaerobic lagoon is a source of periodic complaints from my neighbors. Can I add a small aerator to operate when I get a call that there is a problem?

Aerating anaerobic lagoons is a bit tricky and adding a small amount of aeration is likely to make the odor problem worse rather than better. Aeration is effective when the biological process in the lagoon is changed from anaerobic to aerobic. This means that there is enough oxygen available to supply the total needs of the bacteria that are feeding on the organic matter. Typically this means supplying about two pounds of oxygen for each pound of biologically available organic matter.

By placing a small periodically operated aerator on the lagoon surface, you are not likely to meet the oxygen needs of the system but will be creating an increased surface area for the escape of odorous gases that have already been formed. In doing this you will be making the odors more severe, particularly on a short term basis. Therefore I would suggest that you not plan to aerate the lagoon unless you plan to make the total conversion from the anaerobic process to an aerobic one.

There are not very many attractive alternatives to get short-term odor control. One possibility is to develop a temporary cover by placing a floating layer of straw on the surface. See the next question if you are interested.

10. I have read that putting a layer of straw on top of my anaerobic manure storage basin will reduce the odor. How does this work?

The justification for placing a straw layer floating on top of a manure storage basin goes back to an observation made several years ago that dairy manure storages that had a floating scum layer had less odor than those with a free water surface. It is also common experience that layers of soil effectively remove odorous gases. The concept is one of adsorption and aerobic oxidation. When odorous molecules contact a moist surface whether in the nostrils or in a straw layer, they are captured in the layer and held there. If the moist surface is one containing oxygen, aerobic bacteria are likely to be present and will oxidize the odorous molecule to carbon dioxide and water.

Almost any material can be used as an odor absorbing layer. Straw is a low cost material that tends to float. Some straws float longer than others. By having a straw layer on top of a basin, there is one other process that transpires that is physical in nature. When there is no floating layer on the surface of a basin, the air passing over has direct access to the liquid surface and tends to sweep away any odorous material. When there is a floating layer present, there is an effective barrier which reduces the possibility of the material being swept away. Thus, the more odorous material that can be retained in the liquid phase will decrease that which escapes and contributes to the odor in the surrounding area.

11. Swine manure is typically converted to biogas in Taiwan and several other countries of Southeast Asia. The effluent from these plants is then treated and discharged into streams. Does this approach result in a major odor production problem?

Taiwan is a densely populated country and one for which fresh pork is an important part of the diet. Swine production is typically occurring on highly specialized farms where minimal, if any, cropland is available. As a result, there is seldom an opportunity to utilize manure for its nutritive value. A typical manure handling system will involve the flushing of manure from the building to an anaerobic digestion unit. Effluent from the digester will flow by gravity into a mechanically aerated chamber. The aeration chamber is sufficiently aerated to have a dissolved oxygen of two mg/l or greater. Following aeration, the material will flow to a settling chamber where the solids settle to the bottom and the clear liquid passes over a weir. Solids from the bottom of the settling tank are typically pumped back to the anaerobic digestion tank. In some of these systems, the biogas is claimed as a source of energy for heating water or where needed to warm the nursery and farrowing areas.

Because the anaerobic digestion chambers are sealed to allow the collection of biogas there is little escape of odorous material from these units. The aeration basins are maintained with a sufficiently high dissolved oxygen concentration so that there is relatively little odor release. Thus, while highly energy intensive by U.S. standards and relatively equipment intensive, the system does allow for swine production in close proximity to populated areas and on a limited land base. The fact that no plant nutrient recovery is involved is of concern to some people in the area, but there is relatively little experience in using livestock wastes on the tropical crops grown on these farms. There is, however, a strong tradition of mechanical treatment of wastewater and the discharge of what we would call partially treated effluent. The distance to the ocean is relatively small for many of the farms and the water quality criteria for discharge are more lenient than in many of the pork production areas in the U.S.

12. Pig producers in Holland have been required to reduce the escape of ammonia from their farms. What is the environmental damage of volatilizing ammonia?

Ammonia volatilization has become a major concern throughout Western Europe but most particularly in the Netherlands where there is a high density of livestock production. Volatilized ammonia tends to go in one of two directions after escaping from a livestock or poultry enterprise. It may be oxidized by the various oxidants in the air to produce the full range of nitrous oxides. The nitrous oxides are widely recognized as being major contributors to the acid rain problem. It is because of this problem that ammonia escape is being so severely restricted.

For more than twenty five years, researchers in the U.S. have been aware that ammonia volatilized from manure, particularly from anaerobic lagoons, is being transported downwind and deposited as "dryfall" or being absorbed on nearby water surfaces. Data from California's concentrated dairies indicated that ammonia was being absorbed in sufficiently large quantities to contribute up to eight pounds of nitrogen per acre per week.
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13. What are the compounds responsible for the odor of swine manure?

As researchers began to identify the individual gasses present over decomposing swine manure in a building or in a storage tank, it became obvious there was no single compound nor small group of compounds responsible for the perceived odor. This observation has continued. Casual observation suggests that the odor typically contains compounds that have odors suggestive of ammonia, hydrogen sulfide and some heavier compounds, perhaps indole and skatole. Quantitative measurements, however, show that under conditions when an observer can detect the odor suggesting that ammonia is present, the concentration of ammonia measured in the air is significantly less than the published odor threshold. This is similarly true for hydrogen sulfide and other typical odorants.

The answer to this dilemma seems to lie in the observation from other fields, namely that swine manure odor consists of a complex mixture of organic compounds and the measurement of the easily quantified constituents will not adequately explain the odor. All of this suggests that some of the chemical homologs of the more common odorous compounds are contributing to the perceived odor. Thus, one is prompted to identify the amines, the mercaptans, the organic acids, as well as indole and skatole, as primary odorous substances.

The production of these compounds is most frequently through the anaerobic decomposition of manure. Projecting the biochemical breakdown of complex proteins and carbohydrates in swine feed supports the logical basis to expect these compounds to be formed either as intermediates in the breakdown process or as secondary products as a mixed bacterial population attempts to metabolize the direct breakdown products. The formation of these materials in an aqueous solution provides them an opportunity to volatilize prior to their being further decomposed. This is obviously a dynamic situation. The environment under which volatilization occurs will influence the mixture of compounds in the air. In a similar manner, the mixture of compounds present in the manure at any time and the presence of any effective biological inhibitions will influence the decomposition process and, in turn, the odor perceived.

There are other possible odor sources associated with a large swine confinement system. If dead animals are allowed to remain on the property without proper handling, they will contribute to the odor. If wet feed is allowed to decompose on site, it, too, will influence the odor. Either of these is subject to management control and should not become major issues.

Anaerobic lagoons are the least expensive and currently the most popular means of dealing with swine manure from confinement buildings. They operate with a minimum of management attention, are inexpensive to construct, and provide storage as well as treatment. Unfortunately, they are also prone to release odors from the surface. The compounds are largely the same as listed above. As lagoons increase in surface area, the quantity of anaerobic liquid exposed to the atmosphere increases. As a result, the odors are detectible over a larger downwind area and at larger concentrations than was the case for smaller lagoons.

14. Are there any disease causing bacteria or other microbes in the air downwind of swine facilities that may affect human health?

There is considerable evidence of elevated dust and aerosol concentrations inside livestock and poultry facilities as well as downwind of these facilities and of the land to which manure is being applied with irrigation equipment. As early as 1975 researchers reported elevated numbers of colony forming units (CFU) per liter of air inside a confinement beef building, inside a turkey house as well as downwind from an irrigation sprinkler. In their studies, the number of bacteria carried in the spray tended to decrease rapidly with distance.

The more likely problem of a downwind airborne nature has to do with allergic reactions to the inhalation of organic dusts. The antigenic material in a majority of allergy cases was fungal spores, but protein materials have been implicated in others. The response of individuals to organic dust particles is quite variable and depends on the person's individual immunological reactivity. The hypersensitivity of certain individuals is frequently associated with some immune reaction.

The evidence is quite limited but confirms the anticipation that dusts and aerosols are indeed elevated in the vicinity of livestock enterprises. The observation that odors have been far more frequently mentioned as the offending constituent supports the concept of human resistance to airborne pathogenic microorganisms.

15. I have read that anaerobic lagoons produce methane. Is this the same methane that has been implicated in global warming?

Yes, the methane produced by livestock and by manure decomposition is indeed the same material as is being discussed as contributing to the Greenhouse effect.

Methane is the most abundant organic chemical in the earth's atmosphere. Its abundance is increasing and the quantity in the atmosphere has reached the highest levels in geological time. The greenhouse gases are of importance because they tend to absorb longer infra-red radiation. Methane is a much more potent greenhouse gas than carbon dioxide, for example, on a molecular basis (21 times) and on a mass basis (58 times). Human activity is the major source of methane in the atmosphere. The total methane production is estimated to be 354 Tg (Tg = a million metric tonnes). This budget is best put in perspective by looking at the global budget for methane production as shown in Table 1. The United States is included among the five largest emitting countries (27 Tg CH4 per year). Of that total emission, manure based emissions is 2 Tg.

These data would suggest that livestock manure management systems are in fact contributing to the total methane load being experienced. The prevalence of anaerobic manure treatment (anaerobic lagoons), also highlights the role of confinement livestock production as a greater source than if the same number of animals were being managed in a less intensive manner. One saving factor is the observation that methane production during the anaerobic treatment/storage of manure is highly temperature dependent. Little methane is formed when the liquid temperature is less than 10 C. There is the strong possibility that the global estimates for manure related methane production are inflated because so much of the anaerobic livestock manure handling is done in areas in which the average temperature is inhibiting methane formation for a major part of the year.

These data would seem to suggest that confinement livestock production with conventional manure storage in pits and anaerobic lagoons is contributing to greenhouse gas production, especially methane. The fraction of the total load from this source is small, however, and efforts to reduce that load by changing only manure handling practices would be inconsequential. The good news is that many (most) of the techniques currently being considered to respond to the more immediate odor concerns will reduce methane production as well. Aerobic treatment, soil incorporation, and lagoon covering all reduce methane escape.

16. If I have a digester installed, can I use the methane to power my tractor?

No, biogas is a mixture of methane and carbon dioxide. The carbon dioxide is of no fuel value so is not helpful for fuel use. The methane is a fuel (major ingredient in natural gas) but it does not liquify under pressure as do propane and butane. As a result, a fuel tank to store enough methane to power your tractor for a reasonable time would be so large and so heavy due to the strength required that most everyone agrees that we need to find a use for biogas that is stationary. Most people also agree that we must use the biogas in a way that we can use it on an as-produced basis and not become involved in a storage process.

17. What are the federal laws that apply to odors from swine facilities?

There are no federal regulations directly related to the control of odors from swine facilities or other livestock operations. Thus, you are only concerned about state and local laws and ordinances relative to odors. There is the law of common nuisance, however, which roughly states that every person has the right to the enjoyment of his/her property without unreasonable interference. It is this latter nuisance law that has been of greatest concern to pork producers over the past decades as they have dealt with odor problems.

There are, however, regulations related to worker safety that involve some of the same gasses that are of concern to people involved in odor control.

18. Why is hydrogen sulfide so important in manure management?

Hydrogen sulfide is highly lethal to both humans and livestock. Incidents of animal deaths attributable to hydrogen sulfide toxicity have been reported particularly when manure storage tanks beneath slotted floors have been agitated prior to pumping to a tank truck or an irrigation system. There is no doubt about the likelihood of achieving concentrations of hydrogen sulfide well in excess of the concentration considered toxic to humans (0.05 %) when agitating a manure storage. Hydrogen sulfide is recognized because of its having a typical rotten egg odor that most people associate with high school chemistry laboratories. Unfortunately, at higher concentrations where it is toxic, hydrogen sulfide immediately blocks the olfactory process to the extent that nothing is smelled.

19. What is the best time of day to spread manure if I want to minimize the release of odors?

Odor dispersion is best when the atmosphere is unstable and ground level air is rising because it is warmer than that at higher elevations. Secondly, a manager seeks a time when the air velocity is as high as possible and hopefully in a direction that will carry odors in some direction other than toward the most sensitive neighbor. It is also desirable to apply manure at a time when one can expect a maximum rate of drying so the time during which the surface is wet will be minimized. Taking all of these considerations into account may be difficult, but for most pork producers, this means applying manure during the mid to late morning. As a follow-up, it is desirable to incorporate the manure as quickly as possible if that is indeed part of the plan.

20. Is landscaping such as tree planting and grounds keeping of benefit in avoiding odor complaints?

Anything that a producer can do to indicate they are responsible members of their community is helpful in avoiding complaints. Having a neat, well maintained facility is part of establishing and maintaining that image and will pay dividends in improved relations. The literature is very clear in the association of odors with other stimuli. If an operation is well maintained, neatly painted and appropriately landscaped, it gives the impression of being less likely to emit an unpleasant odor than an operation which suggests a low regard for such amenities. In addition, location of lagoons and other known odor generating components away from the road and where they are less likely to be seen will decrease the visual suggestion of an odor source.
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Pork producers represent a relatively small component of the overall concern over odor control. Accordingly, it is important when designing a research strategy and identifying research opportunities, that pork producers support those research activities that will fill the gaps between other technology development and the needs of pork producers. Stated differently, pork producers are seeking opportunities to adapt research being conducted in the larger odor control arena to meet their specific needs.

Extensive research has been devoted to identifying individual compounds and mixtures that contribute to odors from swine facilities. The list of compounds is long and current consensus is that no single compound or class of compounds adequately describes the odor nor can the control of a single compound provide the necessary odor control. In spite of this, the low cost measurement of certain key representative compounds has provided a convenient indictor of odor intensity and has greatly reduced the cost of odor control research. Olfactory measurements are accepted as the only realistic means of quantifying odor intensity at this time and the costs of conducting these measurements is high. Research is underway in the electronics industry to develop detectors that simulate the response of the human olfactory system. Most observers classify current "odor detectors" as crude and only somewhat indicative of odor levels. Progress continues and better models are likely to appear. At some time, it will become possible to support research that will adapt "odor detectors" to the measurement of odors from livestock production facilities. It is important that when that time arrives, the opportunity be seized.

Downwind odor problems represent a combination of odor production and transport. Both the production and transport mechanisms are variable over time and tend to complicate the assessment of whether an individual farm is achieving a satisfactory degree of odor control. The assessment is further complicated in that not all areas have the same tolerance for odors. There is a temptation to seek an overall standard for acceptable odors. This review of the research, however, suggests that such an overall standard would be inadvisable in that the standard would most likely be based on the needs of the most sensitive location. Thus, the ability of individual locations to achieve odor dilution and to periodically accept detectable odors would be lost. An immediate research need is to better define the interaction between odor production, separation distance, climatic data, and local land use. The urgency of this need has been highlighted by the response of local land owners to the development of large scale intensive facilities in areas previously populated by smaller but more numerous facilities.

Even casual observations over the past twenty years have shown that the reaction to odors from pork production facilities are complex and highly variable. More recently, data have demonstrated the interaction between odor perception and personal anxiety. It will be important to pork producers to remain on the cutting edge of this particular field of study. Currently it is difficult to adequately isolate research questions with definitive answers, but this situation will change over time. It behooves pork producers to remain related to the research community involved in this arena to be certain that in designing facilities provision be made for the individual responses of people of differing backgrounds and interests.
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Considerable progress has been made in the design of swine facilities to maximize animal performance and to optimize labor efficiency. Manure collection and transport facilities have been developed that can be automated, greatly reducing the labor involved in manure handling. Since odors from housing facilities remain one of the frequently cited sources, there remains an opportunity to reduce odors with building design innovations. Manure handling equipment that moves feces and urine from the pen area quickly and completely is still evolving. In addition to prompt and effective manure removal, water use reduction would facilitate low odor treatment and storage capabilities. Neither gutter scrappers nor flush systems fully meet the criteria. Scrappers leave a film of manure for decomposition and odor evolution. Flush systems produce such a dilute manure that enclosed storage and treatment become expensive.

Concrete floors and slats provide a durable surface that in addition provides stable footing for the animals but at the expense of being easily and completely cleaned of manure. Metal, plastic and ceramic materials are more easily cleaned but at the expense of being slippery and prone to animal injury. What are the possibilities of alternate building design and manure collection systems that provide the benefits of safe healthful animal environments but which minimize the amount of surface area on which manure decomposition can be expected?

Ventilation of confinement facilities is designed to remove excess moisture, heat and respired gases from the building. In addition, an effective ventilation system replaces the odorous air with fresh odor free air from the outside. An alternate view is that the ventilation system moves the odorous air from within the building to the outside where it can be diluted and dispersed. There are alternatives. Are there in-house or exhaust air treatment systems that are compatible with animal performance that can reduce the volume or odor intensity of exhaust air? Are passive absorption processes available that can be included in building construction that will selectively absorb odorous materials and convert them to less noxious forms? Can dehumidifiers be incorporated that will have sufficient merit in terms of heat recover and reduced ventilation to justify their incorporation along with an in-building air quality management system?

The impact of ground level structures on air movement and odor dispersion remains an inexact science. Efforts to mathematically model odor transport under low wind velocities particularly under the influence of a temperature inversion have not proven sufficiently reliable to serve as design techniques. Efforts to better predict air movement under highly stable conditions of low wind velocity can prove helpful in the placement of buildings and even in the installation of dispersion devices. It is highly likely there are appropriate places for the location of trees, irrigation equipment, and baffles to promote dispersion under critical odor transport conditions. Certainly, siting decision can be improved with an increased understanding of how local climatology interacts with odor transport.
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Numerous options exist for the treatment and storage of swine manure. In the United States, most management schemes are designed for returning the manure to crop or pasture land as a final disposal or utilization site. Depending upon the land available and the perceived value of the plant nutrients, various levels of nutrient conservation are possible. During recent years there has been a general strategy of designing effluent application strategies on the nitrogen application rates. As the scientific community becomes increasingly aware of the hazards of consistent application of excessive quantities of other nutrients, particularly phosphorous, revised application rates are likely. Changes in the cost of energy as reflected in nitrogen costs are also likely to impact manure disposal decisions. Manure handling systems that conserve rather than volatilize nitrogen are likely to grow in favor. Energy recovery schemes based on biogas production are likely to become of interest again. This research remains a longer term interest and is probably not appropriate yet.

Of greater immediate concern will be the current practice of freely disposing of ammonia and methane to the atmosphere. The Western European countries are already responding to limits on ammonia release. The good news is that systems that reduce ammonia and methane release also tend to reduce odors. The bad news is that these systems will require significant changes in current manure handling practices. There is an opportunity for research to begin at this time that will place pork producers in leadership roles as these concerns become more widespread.

Anaerobic lagoons and manure storage basins have become increasingly widespread in the industry as systems have grown in size. These systems have the advantage of low cost and they effectively reduce the nitrogen content of manure. They are also compatible with hydraulic manure transport systems. Unfortunately, they are also recognized as being among the more odorous alternatives. Because of the cost advantage of lagoons, research on odor control additives to be introduced to lagoons or incorporated in feed rations needs to be done in a controlled manner. The marketplace offers an extensive array of alternatives. The development and implementation of a scientifically sound evaluation scheme to test these products will be of considerable service to pork producers and to the odor control additive industry.

Covers have been installed over lagoons serving the waste treatment needs of a number of industries. Less expensive and more easily managed permeable covers have been proposed for swine lagoons and manure storage tanks. Although each of the cover alternatives add cost to the anaerobic lagoon or storage basin, they are likely to be less expensive than the alternative aerobic systems. There are some potentially productive research opportunities in this particular area.

The other most frequent source of odor complaints is the application of manure to cropland. The problem is particularly present when manure from long term storage is applied using irrigation equipment which creates a large surface area. Alternatives such as direct soil injection, while highly effective, are not applicable in all situations nor are they acceptable to all producers. There is reason to expect there are treatment possibilities that can provide temporary odor control that will be effective during the brief period between removal from the storage unit and absorption by the soil. This may be an opportunity to work with the manufacturers of odor control chemicals on a specific task. Other possibilities are short-term aeration and odor absorption. Dilution with fresh water also has a possibility of being effective. One alternative to be evaluated would be mixing equal parts of stored manure and fresh water to take advantage of the odor absorbing capabilities of clean water.
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In addition to the areas identified that seem to offer particularly attractive opportunities for research to contribute to odor control progress, there should always be an opportunity to respond to innovative ideas. The odor issue is complex and will demand contributions from a variety of research specialists. Requests for research proposals would be made more effective if, in each issue, there is an opportunity for innovative ideas to be proposed, justified and offered for consideration. In addition, those who make funding decisions relative to odor control research will be called upon to remain open in their thinking so that potentially valuable ideas are not rejected just because they fail to meet the preconceived expectations of the evaluators.

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