An Executive Summary

A Review of the Literatureon the

Nature and Control of Odorsfrom

Pork Production Facilities

Prepared by

J. Ronald MinerBioresource Engineering Department

Oregon State UniversityCorvallis, OR

forThe Odor Subcommittee

ofThe Environmental Committee

ofThe National Pork Producers Council

September 1, 1995

TABLE OF CONTENTS

Executive Summary

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

The Olfactory Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Psychological Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Odor Intensity Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Regulatory Efforts to Control Odors . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Climatology and Odor Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Odor Sources Associated with Pig Production . . . . . . . . . . . . . . . . . . . . 5

Application of Manure to Cropland . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Feed Additives to Reduce Odor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Air Treatment Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Producer Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

The Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

The Real Odor Control Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Research Opportunities Having Potential to Reduce Odors . . . . . . 19

EXECUTIVE SUMMARY

The development of highly sophisticated pork production facilities is the combination of bothextensive research and application of innovative production methods. As a result, the porkindustry has experienced rapid growth and increased efficiency in improving hog performance andhuman labor inputs. Along with growth and efficiency has come the concern for controllingodors. Rural and urban neighbors desire a living space free of animal manure odors.

Research has demonstrated odor has at least two aspects. One, the objective portion, is measurableboth 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 pigproduction odors, who have another interest in not smelling the swine odor, or have some otherbasis for their negative feelings toward a swine operation, are generally more likely to complain ofpig production odors. People who see the pork industry as a contributing component of the localeconomy 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 comparedto those systems that do not. The situation is further complicated in that not all locations requirethe same degree of odor control nor are the requirements stable with respect to time. Largeroperations have a larger odor production potential and may find the technologies appropriate forsmall operations are not acceptable for their use.

Two manure management schemes predominate in pork production facilities at this time. One isthe storage of manure as a slurry in one or more pits or tanks immediately beneath the confinementfacility or in a tank located outside the facility. The goal is to transfer the manure into the storagefacility with a minimal dilution of water. There is a continual odor release at the time of agitation inpreparation 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 theproduction of biogas or a permeable cover designed to biologically oxidize the odorous gases asthey 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 nitrogenoriginally in the manure escaping to the overlying air. Proper lagoon design and management areintended to achieve a relatively low intensity of odor release. This approach is effective most of thetime, however, during the late spring as water temperatures increase, elevated odor levels are morefrequent. As lagoons become larger, the odor releasing surface becomes sufficiently large enoughto present an odor control problem.

The Olfactory Process

Odor perception begins well up in the nasal cavity where we humans are outfitted with a collectionof highly specialized receptor cells. As individual odorous molecules are drawn into the nasalcavity, a portion are dissolved in the mucous film that covers these specialized detectors. Once anodorous molecule is captured in the system, it will become attached to one or more of theindividual receptor cells based on a shape match. Depending upon the molecule, it may becaptured by one or several of the specifically shaped receptors. Once a receptor has beenstimulated, an electrical signal is transmitted to the brain and an amazing process is underway.

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Once a signal is generated, the brain takes over and we respond. The reaction may be to fleebecause of an association with danger or it may be to linger because of the perceived desirablesituation. Some writers have asserted that human beings can detect over ten thousand differentodors even though we can identify only a small percentage of these. The sense of smell is muchmore precise than is our ability to describe the odor we have perceived.

Psychological Response

The psychological response to odors is more complex and less well understood than thephysiology which has been extensively explored during the past thirty years. Evidence suggeststhat each of us learns to like or dislike certain odors. Children like almost all smells. It is only aswe mature and begin to talk about the odors that we develop a sense of likes and dislikes. Foodtastes are very much related to the odors from those foods. Subtle spicing would be ineffectiveexcept for the multitude of differences we can detect.

Only recently have scientists begun to relate these complex psychological reactions to the ways inwhich 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 areexperiences of people who react to swine lagoon odors with an emotional intensity that otherswould find entirely unreasonable. Recent observations suggest these are honest and accuratereactions. Whether these responses are so intense because they have an objection to the odorsource based on other factors is unclear at this point. It has been observed, however, that there arefewer objections within a community to those odors that are a traditional part of the community, orare produced by an agricultural operation of an appreciated and esteemed member of thecommunity, than to an odor generated by an outside agent’s operation that may alter the traditionalsocial structure. Thus, a large high tech swine confinement system relocating to an area oftraditional style pork production can expect to have the local residents find the odor moreobjectionable than an odor of similar intensity from a more conventional system of porkproduction.

Odor Intensity Measurements

Odor intensity is usually considered one of the primary factors in deciding whether a problemexists. Several methods of assessing odor intensity have been proposed and used. The mostobvious method is the direct scaling technique. This approach involves asking a panelist or otherunbiased observer to evaluate an odor intensity on a numerical scale. Some researchers haveproposed scales of one to six, others have used one to ten with the higher numbers representing themore intense odors. This technique was used as long as sixty years ago. A modification of thistechnique which improved its usefulness was to also provide the panelist with a standard ofdefined magnitude. This tends to reduce the variability among panelists.

Referencing is an alternate technique. The panelist is asked to compare the intensity of anunknown odor with a series of different concentrations of a reference odorant. The panelistindicates whether the odorant being evaluated is more, less, or of the same intensity as a particularstandard. The most common standard is 1-butanol because of its being available in a highlypurified form, low toxicity, high stability, and its reasonably agreeable odor. Olfactometers basedon 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 airsamples into the testing site. Exposing fabric swatches to odor sources and then comparing thoseswatches has been proposed as an alternative to either transporting the odorous air to panelists or totransporting panelists to an odor source.

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Dilution, either liquid or vapor, has been used as an approach to evaluate odor intensity. Althoughseveral techniques have been used, all are similar in concept. Panelists are presented samples ofdiluted odors to determine the dilution of the odor they can barely distinguish from an odorlesssample. Both liquid and gas comparisons have been conducted. The equipment for thesecomparisons range from the relatively simple to the highly complex. The Scentometer, acommercially manufactured device, can be taken to the field and diluted samples of the ambient aircompared to an odor free air. Scentometer evaluations of odor intensity have been widely usedbecause of the low cost and convenience of the tool. More precise dilution olfactometers are inwidespread use for research purposes. The devices are all similar in that they deliver dilutedsamples 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 aconstituent that is present in the odorous air and is easily measured. This approach has particularappeal 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 regardto manure odors. Although most researchers seem to agree that neither is the major constituent ofswine manure odors, their removal or reduction in concentration has generally been used as anacceptable surrogate for odor removal. Volatile organic acid concentrations have also been used asan 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 odorintensity measurement. If such a device was available it would contribute a degree of objectivity tothe odor measurement process. Most detectors currently available respond to a particularconstituent so they would not be appropriate for a complex odor like that from a manure lagoon. Abroad range electronic detector has been manufactured and was proposed as an odor measuringdevice. However, initial testing at cattle feedlots and dairies was not encouraging.

Regulatory Efforts to Control Odors

Swine odors are not regulated by federal statutes nor by the air pollution control agencies of any ofthe states. Many states, however, have expressed concern over the complaint they have receivedfrom 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 beequally difficult to enforce. As an alternative, several states and local units of government haveestablished regulatory guidelines concerning the construction of swine facilities that are designed toindirectly reduce odor complaints. One of the approaches is to specify the minimum requiredseparation distances between confinement buildings and nearby residences or public gatheringareas. Another has been to restrict the use of anaerobic lagoons. A third approach has been toinsist on a minimum area for manure disposal to be located in close proximity to confinementsystems. 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 pursuitsfrom the encroachment of housing development into areas of established agriculture. The goal wasto avoid lawsuits that were resulting from having persons unfamiliar with agricultural odorsattempting to halt or change established agricultural practices because of their having moved intothe area. The provision of the various “Right to Farm” laws are different and the protectedpractices vary from one state to another. Most protect the opportunity to spread manure oncropland. Others provide an establishment time. Any agricultural practice that has been continuingfor that time or longer is protected from the arrival of new residents or the development of newconcerns by existing neighbors.

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The most frequent threat to swine producers relative to odors are the private or public nuisancesuits that have been filed at various locations around the country. Nuisance litigation is based onthe concept that no one has the right to unreasonably interfere with another’s right to enjoy his/herproperty. When present at unreasonable concentrations or for unreasonable times, odors havebeen considered sufficiently important to have been judged a nuisance on several occasions. Eachcase must be considered separately and the judge/jury generally evaluates each location separatelyin deciding what can be considered an unreasonable odor level. Where a nuisance has been judgedto exist, damages may be assessed against the odor source. Damages may be actual for medicalcosts, alternate housing, or for more frequent cleaning of furniture or draperies. Punitive damagesmay also be assessed where it is decided that some additional payment is in order because theodors were caused by negligence and irresponsible actions. Nuisance lawsuits have been heard inalmost all of the major livestock producing states and have proven to be an expensive alternativefor those producers who have become directly involved.

Climatology and Odor Transport

Odors released into the environment are transported by wind and subsequently diluted byatmospheric turbulence. Turbulence increases with greater wind velocities and with the presenceof surface roughness such as hedges, trees, and buildings. Incoming solar energy warms the earthsurface. Some of that absorbed heat is transmitted to the air, which expands as it warms, creatingan upward buoyancy. This unstable condition contributes to the normal process whereby odorsare dissipated in the environment. The Gaussian plume dispersion equation has been adopted asthe most common starting point in attempts to predict the extent and concentration of downwindodor concentrations. This highly theoretical model has the advantage of being amenable tomathematical solution, but in exchange it ignores many of the local topographical features that areimportant in understanding odor transport.

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

The combination of air velocity and temperature changes can cause some unexpected odor transportresults. For example, during a clear night of low wind velocity, cold air can flow down a hill andfill 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 ofanimal waste related odors have been used in the Netherlands and are sometimes required inAustralia. They have not been applied to the siting of livestock facilities in the United Statesbecause of the problems inherent in the process. Standard Gaussian plume models are notdesigned to simulate atmospheric pollutant transport over rough terrain or around objects, nor dothey account for vegetation effects.

Odor Sources Associated with Pig Production

Odorous gases can be produced at a number of sites around a livestock enterprise. The mostcommon odor sources, however, are the floor and other surfaces of buildings and pens, thesurfaces of animals, the manure collection and storage facilities, feed storage facilities, dead animaldisposal and storage areas, and manure exposed to the air during land application. Each of theseodor sources has received research attention, and technologies exist that can be employed inresponse to the issue. One of the unresolved issues is the matter of the need for odor control and

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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 productiontechnology has changed, pork producing enterprises have grown in size, and as rural residentshave become less tolerant of invading odors from nearby pork production operations, the need toaddress the odor management questions has become more acute.

Odors from the floor, pen partitions and the bodies of confined animals have been a serious issuethat has been reduced as designers have become better informed about how to design buildings thatpromote clean animals and clean pens. The use of slotted floors and flushing gutters havesimplified the separation of manure from animals. Early confinement buildings reflected a limitedunderstanding of swine physiology and ventilation needs. As a result, dirty, manure-coveredanimals were not uncommon. Animals were forced to roll in manure as a source of cooling. Dirtyanimals 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 thatanimals are maintained at a comfortable temperature and that the design of the pen provides anopportunity for pigs to remain clean, dry and manure-free. Misting equipment has been added tobuildings in warm climates to provide helpful evaporative cooling to animals. By minimizing theamount of manure on pen floors and along partitions, the amount of odorous gas is reduced. Cleananimals 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 thedesired 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 controlresearch because of the earlier observation that this is the odor source of greatest importance todownwind neighbors. Storage of manure both underfloor and outside the building storagestructures is being widely used. The underfloor storage tanks are generally designed for aminimum of water addition to extend the storage capability. Most underfloor storages are allowedto stand quiescent. One exception has been the use of underfloor oxidation ditches which werepopular during the seventies. With adequate mechanical aeration, the storages could be maintainedat markedly reduced odor levels. In addition, much of the nitrogen was lost by alternatenitrification - denitrification. Although the process improved the quality of the buildingenvironment, 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 exhaustventilation capacity above the manure level and below the slotted floor to reduce the upwardmovement 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 shallowgutters, flushed gutters that are located beneath slotted floors or are open to the animals, and shortterm 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 beenblamed for elevated building odor levels because of the residual manure that is left. Both open andunderfloor flushed gutters offer the possibility of removing manure on a daily or more frequentbasis, the use of recycled effluent as flush water, and a system that is easily automated. The filland dump pits are also easily adapted to the use of recycled water and have the possible advantagethat the manure is continuously covered with water. By being covered with water, there is lessodor generating surface exposed to the air.

Exterior manure storages may be either above or below ground. The below ground manurestorages may be in a water tight tank made of concrete or some other impervious material. Thattank may be partially covered to reduce the rate of air exchange between the manure and theambient air. Alternatively it may be open. Safety is a critically important aspect of manure storagetank design. All manure storage tanks should have safety guards that prevent accidentally falling

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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 previouslyquiescent tank of manure will release a large quantity of potentially lethal gases. Pork producersshould protect themselves, their families, their employees and livestock from both suffocation andgas toxicity. They should not stand over or adjacent to manure storage tanks as they begin toagitate. Odor problems from underground manure storages can be reduced by keeping the tankscovered. Most odor complaints occur when the tanks are agitated or being emptied. If manure isbeing loaded into a trailer or truck mounted tank, agitation and splashing can be minimized byproper 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 opportunityfor anaerobic bacteria to convert manure volatile solids into liquids and gases such as methane andcarbon dioxide. Lagoons result in a large portion of the nitrogen originally in the manure escapingto the overlying air. Proper lagoon design and management are intended to achieve a relatively lowintensity odor release. This approach is effective most of the time; however, during the late springas 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 alarger area and potentially a greater number of people. Odor concerns around anaerobic lagoonsinclude the ongoing escape of odors from the surface and the more extensive escape at the time ofremoving 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, increasingthe volume of lagoon relative to the organic loading. Lagoon loading rates are typically expressedas lagoon volume per pound liveweight of animal served. Recommended volumes range from 1.5to 3.0 cubic feet per pound of pig being served depending upon location. Lagoons in the southernpart of the U.S. can be smaller because of the warmer temperatures. Overloaded lagoons, thosewith less than the suggested volume, are generally considered as being more odorous. In quest ofodor reduction and operational efficiency, the American Society of Agricultural Engineers hasadopted a standard design practice for anaerobic lagoons that incorporates low volatile solidsloading rates and necessary storage of liquids and solids.

Chemical and biological additives, masking agents, and other products have been proposed and arecommercially available for use in lagoons or manure storage systems. Typically, they areproposed to improve lagoon performance, liquify the accumulated solids and reduce odors. Thereis little supporting data, however, to document the success of these materials. There is generallyno shortage of well acclimated bacteria in the lagoon nor is there a problem with low pH in aproperly designed and well operated lagoon.

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

Two types of lagoon covers have also been proposed. Impervious covers, rubber or plasticmaterial, 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 byventing into a soil bed. Impervious covers have proven effective in reducing the odor of lagoonsbut have not been widely adopted by pork producers because of the cost involved. Researchershave 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 acommercial product.

Aeration is an alternative that is available to designers of lagoons and other storage units. By theaddition of mechanical aerators, the anaerobic process can be converted into an aerobic one with

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the associated odor control benefits. Most often, when an aeration process is selected, a portion ofthe organic loading is removed by some other process, either sedimentation or screening toseparate the solids, or anaerobic decomposition in an enclosed environment. Thus, one potentialmanure handling system would include a solid liquid separator followed by an aerated storagelagoon. 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 wayto reduce the land area required for manure management and reduce odor release, and to claim aportion of the energy as a biogas fuel or as locally generated electrical energy. These systems arewidely used in Asia but have had little appeal in the U.S. because of the higher operating costs andthe greater initial investment. The technology is available for the construction of manure handlingequipment of this type.

Application of Manure to Cropland

Land application is the final step in most swine manure handling schemes. This step is a frequentcause of odor complaints because it creates a large surface area from which volatile compounds canescape. The most frequent response to this concern is to modify the application procedure toaccommodate neighbors. Frequently, complaints can be avoided by selecting a time to haulmanure when the wind will blow odors away from the sensitive areas. Application of manure inthe early part of the day when there will be better drying conditions will also help. Obviously, it isthoughtful to avoid spreading manure immediately prior to a holiday or weekend when you mightexpect neighbors to be planning outdoor entertainment. Prompt incorporation of the spreadmanure into cropland will also help in avoiding odors. Soil injection is the most effective way toreduce the escape of odor during land application. Soil injection is also helpful in reducingammonia loss.

Application of lagoon contents is a necessity to maintain a stable chemical balance in the lagoonsystem with respect to salinity and ammonia. One method, irrigation, is particularly prone to odorrelease and complaints triggered by visibility as well a odor detection. Irrigation equipment will behelpful in reducing the time required for application but will require considerable managementattention to avoid creating problems. Low pressure sprinkle systems create less air water contactthan high pressure systems. Irrigation from lightly loaded well managed, anaerobic lagoons andfrom second stage or tertiary lagoons will provide effluent of higher quality and less odor.

Feed Additives to Reduce Odor

There have been several attempts to reduce manure handling odors by altering the ration being fedor by the addition of specific odor reducing material, such as sagebrush, mint oil and a sarsaponinextract of the yucca plant. Although the data from these materials are not conclusive, they suggestthat it is possible to alter the odor of fresh manure; however, that change does not persist once themanure undergoes anaerobic storage.

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

Even less developed at this time is the possibility of manipulating the microbiological populationsin the digestive tract to enhance animal performance and minimize nutrient excretion. This

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approach has potential triple benefit in reducing feed costs, manure handling, and the need forantibiotics to control disease organisms.

Air Treatment Alternatives

Various means to reduce the odor of air have been employed in those industries with long termodor concerns. Absorption and adsorption processes have the potential to remove many of thechemical compounds identified in swine building exhaust. Activated carbon adsorption is widelyused in these industries but has obvious limitations when considered for livestock enterprisesbecause 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 poultryindustries has been to pass odorous air through a shallow soil absorption bed. In this process aunit similar to a septic tank absorption bed was constructed into which the exhaust air wasdischarged. By having the bed relatively large, the headloss was reasonable and by passing the airupward through the soil layer, odor removal was achieved.

Producer Options

Research is generally long on data and short on practical conclusions. If a review of the odorcontrol literature is to be of benefit to the pork producers in this country and elsewhere, it musthave some practical conclusions.

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

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

Although fresh swine manure has an odor, this odor is generally regarded as being much lessobjectionable to nearby residents than that of anaerobic decomposing manure. This means that themost 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 tocropland using irrigation equipment; (d) solid manure when applied to cropland and notincorporated; 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 andequipment 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 becovered, or they can be enlarged to reduce the loading rate and odor intensity. Liquid manure canbe injected directly into cropland and solid manure can be plowed into the ground immediately afterapplication. Spoiled feed and dead animal handling systems are available that can eliminate thisissue.

Unfortunately, if an odor problem exists, each of the odor solutions listed above costs more thanthe current way manure is being handled. Research has not identified an odor control technologythat costs less than doing nothing. Many producers have sought lagoon additives that wouldeliminate odors. Industry has tried without success to find such a product.

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Atmospheric modeling can be used to evaluate downwind odor transport; however, no model hasbeen able to provide the separation necessary to protect a confinement building that was placed tooclose to a neighboring resident.

The Future

Odor control is of increasing concern as pork production moves into ever larger units and thesurrounding residents have a less direct relationship to animal agriculture. Conventional systemshave devoted little direct investment to the control of odors. The future clearly demands that oursystems become more effective in these matters. Additional research in this area is obviouslyimportant, but in the immediate future, application of those technologies available will be requiredto a greater extent. Aerobic systems and enclosed anaerobic breakdown of manure have obviousapplication. The use of enclosed manure storages and direct soil injection is possible in manylocations where it is only marginally practiced at this time.

Of paramount importance to the success of present day systems is to avoid overly optimisticassumptions in assessing manure production and treatment efficiencies in the design of storage,treatment and land disposal systems. Overly optimistic design assumptions in these areas havefrequently been utilized to justify placing an operation on a particular parcel of land that is in realitytoo small. These short term expediencies result in operations that are more likely to lead to eitherodor 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 includinginconvenient retrofits and neighborhood conflicts in later years.

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The Real Odor Control Questions

Research on any topic of importance provides lots of valuable information that is of intense interestto most of us. Unfortunately, in many cases, the information is not directly responsive to ourquestions at any particular moment. In order to overcome this particular interest, the authors of thisreview have attempted to listen to the various producers with whom they have spoken and usedthose conversations as a basis for identifying the most frequently asked questions. Those questionsand our responses based on the literature review follow.

1 . I recently received a telephone call from a person living more than two milesaway from my farm. She said they could smell my pig barn. Is it reasonableto 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 tobe transported a much greater distance than normal without the normal amount of dilution anddispersion. Temperature inversions are one of the phenomena that contribute. When aninversion occurs close to the ground it means there is a dense layer of air near the ground thathas a lighter layer both above and below it. This dense layer of air effectively restricts mixingto that zone beneath the inversion layer.

A second feature that may cause odors to be transported a greater distance than normal is alow wind velocity and a lack of physical features that create turbulence. As wind velocitiesdecrease, there is less turbulence and less dilution of escaping odors. Most odors associatedwith pork production are also greatest during warm weather. Warm weather promotes morerapid biological activity and greater volatility of odorous compounds. As a result, odors aregenerally 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 manyareas, odor transport in excess of two miles has been noted. The good news is that theseconditions that promote ideal odor transport are relatively infrequent.

2 . One of the neighbors who has been complaining about the odor from my farmhas 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 theodor of manure. Similarly, people have reported headaches, stomach cramps, and otherdisorders when encountering odors from a number of different sources even though therewas no evidence to indicate there was anything present in the air that would have caused theowner of the farm or any of his employees to suffer similar symptoms. Thus, people arehighly variable in their response to odors. These different responses come from a variety ofexperiences as well as some very particular differences in how we respond to specificstimulants. Some people are highly allergic to individual pollens. For others of us they are noparticular problem. There is no reason to expect that all of the human bodies would respondexactly to a certain odor.

In addition to those differences that can be attributed to physiological variability, there arealso differences based on our individual memories and the experiences which have shapedour lives. A person whose family raised swine and won prizes with them is almost certain toreact to the smell of pork farms differently from a person who has never been around farmanimals and lives under the illusion that swine are dirty and unsavory critters. Having been

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fired by a particular operation invariably causes the odor of that enterprise to deteriorate inquality. These may seem a trifle humorous but these are real phenomena and if we are tomake 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 toexpect 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 atthe top of a hill. Since there was an odor source near the top of this hill, the odorous airmight, on a calm early morning hour, actually move down the hill along with the cold heavierair displacing lighter warm air. The residents of the valley were exposed to the odor at fargreater concentrations than would be predicted by any of the conventional modelingtechniques. The good news is that this was a most unusual situation and the valley residentsdid 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 afterthe odor source is no longer available?

Yes, odors are quite effectively absorbed onto fabrics. Common experience supports thisobservation as does more controlled research. Any of us who have faced the family laundryare aware that fabrics absorb odors. Researchers have actually used freshly laundered fabricsas a way to capture odors and return a sample to the laboratory or to the home of theconcerned neighbors to be certain the odor they were smelling was indeed coming from thesupposed source.

5 . I have received numerous advertisements suggesting that if I purchase acertain feed additive it will reduce the odor of the lagoon. Have thesematerials been tested and are they effective?

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

This observation is consistent with what would be expected from a consideration of thebiochemistry involved. If animals are fed a ration that meets the basic nutritional needs of theanimal, it will contain about the same level of protein and energy of another ration withdifferent ingredients. If the manure from these animals is stored under an environment thatpromotes their degradation to CO2 and water, about the same quantity of intermediatecompounds 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 lagoonsby supplementing the enzymes and thereby reducing the odor. Have theyproven effective?

A well designed anaerobic lagoon will undergo active biological action during the summermonths when the water temperature is sufficiently warm. Under these conditions, there is anabundance 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 wellacclimated enzyme will have a noticeable impact on the odor being released or on the extentof biological activity underway. Controlled laboratory evaluations of these products have

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only recently been undertaken. Those that have been conducted to date have confirmed theprojection that the addition of a small amount of additional enzyme is not likely to alter thedecomposition 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 latespring and early in the summer. What causes this?

If a lagoon is producing a greater odor intensity than is considered appropriate, there aresome 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. Onesolution is to enlarge the lagoon. Another is to reduce the load. The load can be reduced byinstalling a solid-liquid separator or passing the manure through a settling basin ahead of thelagoon. The load can also be reduced by passing all or a portion of the waste stream throughan enclosed digester and claiming some biogas.

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

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

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

The process is a workable one. The problems are that having a relatively dry manure withwhich to start is not compatible with current liquid manure systems.

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 tomake the odor problem worse rather than better. Aeration is effective when the biologicalprocess in the lagoon is changed from anaerobic to aerobic. This means that there is enoughoxygen available to supply the total needs of the bacteria that are feeding on the organicmatter. Typically this means supplying about two pounds of oxygen for each pound ofbiologically available organic matter.

By placing a small periodically operated aerator on the lagoon surface, you are not likely tomeet the oxygen needs of the system but will be creating an increased surface area for theescape of odorous gases that have already been formed. In doing this you will be making the

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odors more severe, particularly on a short term basis. Therefore I would suggest that you notplan to aerate the lagoon unless you plan to make the total conversion from the anaerobicprocess to an aerobic one.

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

10. I have read that putting a layer of straw on top of my anaerobic manurestorage 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 backto an observation made several years ago that dairy manure storages that had a floating scumlayer had less odor than those with a free water surface. It is also common experience thatlayers of soil effectively remove odorous gases. The concept is one of adsorption and aerobicoxidation. When odorous molecules contact a moist surface whether in the nostrils or in astraw layer, they are captured in the layer and held there. If the moist surface is onecontaining oxygen, aerobic bacteria are likely to be present and will oxidize the odorousmolecule to carbon dioxide and water.

Almost any material can be used as an odor absorbing layer. Straw is a low cost material thattends to float. Some straws float longer than others. By having a straw layer on top of abasin, there is one other process that transpires that is physical in nature. When there is nofloating layer on the surface of a basin, the air passing over has direct access to the liquidsurface and tends to sweep away any odorous material. When there is a floating layerpresent, there is an effective barrier which reduces the possibility of the material being sweptaway. Thus, the more odorous material that can be retained in the liquid phase will decreasethat which escapes and contributes to the odor in the surrounding area.

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

Taiwan is a densely populated country and one for which fresh pork is an important part ofthe 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 forits nutritive value. A typical manure handling system will involve the flushing of manurefrom the building to an anaerobic digestion unit. Effluent from the digester will flow bygravity into a mechanically aerated chamber. The aeration chamber is sufficiently aerated tohave a dissolved oxygen of two mg/l or greater. Following aeration, the material will flow toa settling chamber where the solids settle to the bottom and the clear liquid passes over aweir. Solids from the bottom of the settling tank are typically pumped back to the anaerobicdigestion tank. In some of these systems, the biogas is claimed as a source of energy forheating 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 islittle escape of odorous material from these units. The aeration basins are maintained with asufficiently 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 alimited land base. The fact that no plant nutrient recovery is involved is of concern to somepeople in the area, but there is relatively little experience in using livestock wastes on thetropical crops grown on these farms. There is, however, a strong tradition of mechanical

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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 qualitycriteria 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 ofammonia from their farms. What is the environmental damage of volatilizingammonia?

Ammonia volatilization has become a major concern throughout Western Europe but mostparticularly 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 orpoultry enterprise. It may be oxidized by the various oxidants in the air to produce the fullrange of nitrous oxides. The nitrous oxides are widely recognized as being majorcontributors to the acid rain problem. It is because of this problem that ammonia escape isbeing so severely restricted.

For more than twenty five years, researchers in the U.S. have been aware that ammoniavolatilized from manure, particularly from anaerobic lagoons, is being transporteddownwind and deposited as "dryfall" or being absorbed on nearby water surfaces. Data fromCalifornia's concentrated dairies indicated that ammonia was being absorbed in sufficientlylarge quantities to contribute up to eight pounds of nitrogen per acre per week.

13. What are the compounds responsible for the odor of swine manure?

As researchers began to identify the individual gasses present over decomposing swinemanure in a building or in a storage tank, it became obvious there was no single compoundnor small group of compounds responsible for the perceived odor. This observation hascontinued. Casual observation suggests that the odor typically contains compounds that haveodors suggestive of ammonia, hydrogen sulfide and some heavier compounds, perhapsindole and skatole. Quantitative measurements, however, show that under conditions whenan observer can detect the odor suggesting that ammonia is present, the concentration ofammonia measured in the air is significantly less than the published odor threshold. This issimilarly true for hydrogen sulfide and other typical odorants.

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

The production of these compounds is most frequently through the anaerobic decompositionof manure. Projecting the biochemical breakdown of complex proteins and carbohydrates inswine feed supports the logical basis to expect these compounds to be formed either asintermediates in the breakdown process or as secondary products as a mixed bacterialpopulation attempts to metabolize the direct breakdown products. The formation of thesematerials in an aqueous solution provides them an opportunity to volatilize prior to their beingfurther decomposed. This is obviously a dynamic situation. The environment under whichvolatilization 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 effectivebiological inhibitions will influence the decomposition process and, in turn, the odorperceived.

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There are other possible odor sources associated with a large swine confinement system. Ifdead animals are allowed to remain on the property without proper handling, they willcontribute to the odor. If wet feed is allowed to decompose on site, it, too, will influence theodor. 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 dealingwith swine manure from confinement buildings. They operate with a minimum ofmanagement 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 arelargely the same as listed above. As lagoons increase in surface area, the quantity ofanaerobic liquid exposed to the atmosphere increases. As a result, the odors are detectibleover a larger downwind area and at larger concentrations than was the case for smallerlagoons.

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

There is considerable evidence of elevated dust and aerosol concentrations inside livestockand poultry facilities as well as downwind of these facilities and of the land to which manureis being applied with irrigation equipment. As early as 1975 researchers reported elevatednumbers 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, thenumber 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 tothe inhalation of organic dusts. The antigenic material in a majority of allergy cases wasfungal spores, but protein materials have been implicated in others. The response ofindividuals to organic dust particles is quite variable and depends on the person's individualimmunological reactivity. The hypersensitivity of certain individuals is frequently associatedwith some immune reaction.

The evidence is quite limited but confirms the anticipation that dusts and aerosols are indeedelevated in the vicinity of livestock enterprises. The observation that odors have been farmore frequently mentioned as the offending constituent supports the concept of humanresistance to airborne pathogenic microorganisms.

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

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

Methane is the most abundant organic chemical in the earth’s atmosphere. Its abundance isincreasing and the quantity in the atmosphere has reached the highest levels in geologicaltime. The greenhouse gases are of importance because they tend to absorb longer infra-redradiation. 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 majorsource 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 globalbudget for methane production as shown in Table 1. The United States is included amongthe five largest emitting countries (27 Tg CH4 per year). Of that total emission, manure-based emissions is 2 Tg.

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Global Anthropogenic Methane Emissions by Source for 1990.

CategoryEstimated Emissions

Tg Methane

Livestock, ruminants 80

Rice cultivation 65

Natural gas and oil systems 51

Biomass burning 48

Liquid wastes 35

Coal fuel cycle 30

Landfills 27

Livestock manure 14

Minor industrial sources 4

Total 354

Source: USEPA. 1994. International Anthropogenic Methane Emissions: Estimates for 1990. Edited byM. J. Adler. United States Environmental Protection Agency, Office of Policy Planning and Evaluation.EPA 230-R-93-010.

These data would suggest that livestock manure management systems are in fact contributingto the total methane load being experienced. The prevalence of anaerobic manure treatment(anaerobic lagoons), also highlights the role of confinement livestock production as a greatersource 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 anaerobictreatment/storage of manure is highly temperature dependent. Little methane is formed whenthe liquid temperature is less than 10 C. There is the strong possibility that the globalestimates for manure related methane production are inflated because so much of theanaerobic livestock manure handling is done in areas in which the average temperature isinhibiting methane formation for a major part of the year.

These data would seem to suggest that confinement livestock production with conventionalmanure 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, andefforts to reduce that load by changing only manure handling practices would beinconsequential. The good news is that many (most) of the techniques currently beingconsidered to respond to the more immediate odor concerns will reduce methane productionas well. Aerobic treatment, soil incorporation, and lagoon covering all reduce methaneescape.

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 fuelvalue so is not helpful for fuel use. The methane is a fuel (major ingredient in natural gas) butit does not liquify under pressure as do propane and butane. As a result, a fuel tank to storeenough methane to power your tractor for a reasonable time would be so large and so heavydue to the strength required that most everyone agrees that we need to find a use for biogas

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that is stationary. Most people also agree that we must use the biogas in a way that we canuse 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 orother livestock operations. Thus, you are only concerned about state and local laws andordinances relative to odors. There is the law of common nuisance, however, which roughlystates that every person has the right to the enjoyment of his/her property withoutunreasonable interference. It is this latter nuisance law that has been of greatest concern topork 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 samegasses 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 deathsattributable to hydrogen sulfide toxicity have been reported particularly when manure storagetanks beneath slotted floors have been agitated prior to pumping to a tank truck or anirrigation system. There is no doubt about the likelihood of achieving concentrations ofhydrogen 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 atypical rotten egg odor that most people associate with high school chemistry laboratories.Unfortunately, at higher concentrations where it is toxic, hydrogen sulfide immediatelyblocks 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 therelease of odors?

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

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

Anything that a producer can do to indicate they are responsible members of their communityis helpful in avoiding complaints. Having a neat, well maintained facility is part ofestablishing and maintaining that image and will pay dividends in improved relations. Theliterature is very clear in the association of odors with other stimuli. If an operation is wellmaintained, neatly painted and appropriately landscaped, it gives the impression of being lesslikely to emit an unpleasant odor than an operation which suggests a low regard for suchamenities. In addition, location of lagoons and other known odor generating componentsaway from the road and where they are less likely to be seen will decrease the visualsuggestion of an odor source.

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Research Opportunities Having Potential to ReduceOdor Complaints

Odor remains a complex issue with both a measurable component based on the presence of smallamounts of specific gas molecules and a more subjective component based upon individualsensitivity and personal history. Pork producers are not unique in their concern for odor control.Many industries have invested millions of dollars in their drive to minimize odors; others areinvesting millions to create odors that will attract customers and sell products. Each of the groupsis investing heavily in research to better measure odors, to determine the relationship betweenodorous compounds and human response, to control odor emission, and to reduce the cost of odorcontrol and enhance the benefits of creating desirable odors.

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 researchopportunities, that pork producers support those research activities that will fill the gaps betweenother technology development and the needs of pork producers. Stated differently, pork producersare seeking opportunities to adapt research being conducted in the larger odor control arena to meettheir specific needs.

Odor Identification and Measurement

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

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

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Even casual observations over the past twenty years have shown that the reaction to odors frompork production facilities are complex and highly variable. More recently, data have demonstratedthe interaction between odor perception and personal anxiety. It will be important to porkproducers to remain on the cutting edge of this particular field of study. Currently it is difficult toadequately isolate research questions with definitive answers, but this situation will change overtime. It behooves pork producers to remain related to the research community involved in thisarena to be certain that in designing facilities provision be made for the individual responses ofpeople of differing backgrounds and interests.

Building Design

Considerable progress has been made in the design of swine facilities to maximize animalperformance and to optimize labor efficiency. Manure collection and transport facilities have beendeveloped that can be automated, greatly reducing the labor involved in manure handling. Sinceodors from housing facilities remain one of the frequently cited sources, there remains anopportunity to reduce odors with building design innovations. Manure handling equipment thatmoves feces and urine from the pen area quickly and completely is still evolving. In addition toprompt and effective manure removal, water use reduction would facilitate low odor treatment andstorage capabilities. Neither gutter scrappers nor flush systems fully meet the criteria. Scrappersleave a film of manure for decomposition and odor evolution. Flush systems produce such a dilutemanure that enclosed storage and treatment become expensive.

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

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

The impact of ground level structures on air movement and odor dispersion remains an inexactscience. Efforts to mathematically model odor transport under low wind velocities particularlyunder the influence of a temperature inversion have not proven sufficiently reliable to serve asdesign techniques. Efforts to better predict air movement under highly stable conditions of lowwind velocity can prove helpful in the placement of buildings and even in the installation ofdispersion 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 localclimatology interacts with odor transport.

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Manure Management Systems

Numerous options exist for the treatment and storage of swine manure. In the United States, mostmanagement schemes are designed for returning the manure to crop or pasture land as a finaldisposal or utilization site. Depending upon the land available and the perceived value of the plantnutrients, various levels of nutrient conservation are possible. During recent years there has been ageneral strategy of designing effluent application strategies on the nitrogen application rates. Asthe scientific community becomes increasingly aware of the hazards of consistent application ofexcessive quantities of other nutrients, particularly phosphorous, revised application rates arelikely. Changes in the cost of energy as reflected in nitrogen costs are also likely to impact manuredisposal decisions. Manure handling systems that conserve rather than volatilize nitrogen are likelyto grow in favor. Energy recovery schemes based on biogas production are likely to become ofinterest 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 andmethane to the atmosphere. The Western European countries are already responding to limits onammonia release. The good news is that systems that reduce ammonia and methane release alsotend to reduce odors. The bad news is that these systems will require significant changes incurrent manure handling practices. There is an opportunity for research to begin at this time thatwill place pork producers in leadership roles as these concerns become more widespread.

Anaerobic lagoons and manure storage basins have become increasingly widespread in the industryas systems have grown in size. These systems have the advantage of low cost and they effectivelyreduce the nitrogen content of manure. They are also compatible with hydraulic manure transportsystems. 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 tolagoons or incorporated in feed rations needs to be done in a controlled manner. The marketplaceoffers an extensive array of alternatives. The development and implementation of a scientificallysound evaluation scheme to test these products will be of considerable service to pork producersand to the odor control additive industry.

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

Application of Manure to Cropland

The other most frequent source of odor complaints is the application of manure to cropland. Theproblem is particularly present when manure from long term storage is applied using irrigationequipment which creates a large surface area. Alternatives such as direct soil injection, whilehighly effective, are not applicable in all situations nor are they acceptable to all producers. Thereis reason to expect there are treatment possibilities that can provide temporary odor control that willbe effective during the brief period between removal from the storage unit and absorption by thesoil. This may be an opportunity to work with the manufacturers of odor control chemicals on aspecific task. Other possibilities are short-term aeration and odor absorption. Dilution with freshwater also has a possibility of being effective. One alternative to be evaluated would be mixingequal parts of stored manure and fresh water to take advantage of the odor absorbing capabilities ofclean water.

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Innovative Ideas are Always Welcome

In addition to the areas identified that seem to offer particularly attractive opportunities for researchto contribute to odor control progress, there should always be an opportunity to respond toinnovative ideas. The odor issue is complex and will demand contributions from a variety ofresearch specialists. Requests for research proposals would be made more effective if, in eachissue, there is an opportunity for innovative ideas to be proposed, justified and offered forconsideration. In addition, those who make funding decisions relative to odor control research willbe called upon to remain open in their thinking so that potentially valuable ideas are not rejected justbecause they fail to meet the preconceived expectations of the evaluators.

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