March 1, 1995
The use of a brand name in this document does not constitute an endorsement or recommentdation by North Carolina State University or any member of the Swine Odor Task Force.
The Not-So-Simple Problem of Swine Odors
North Carolina's Swine Industry
The Swine Odor
Recent and Current Research Projects at NCSU
The Not-So-Simple Problem of Swine Odors
For some, the problem seemed as simple as a punchline: pigs stink. Why did it take a team of specialists to figure that one out?
And the simple answer was, it didn't.
We knew, for instance, that a clean pig had about the same amount of body odor as a clean human being.
And we knew, in general, why the swine-odor problem was suddenly finding its way into headlines and public debates. During 1994, North Carolina became the second leading hog-producing state in the U.S., trailing only Iowa. In just four years, production had doubled. No industry in our state had ever grown so large so fast.
Most of this growth came from operations housing hundreds or thousands of pigs at one site. With so many animals under roof, it was difficult to manage wastes and keep things clean. At the same time, development in once-rural areas was bringing more people into contact with farms. In many communities, complaints about odor began making the news.
For anyone with something at stake, there was nothing simple or funny about an industry worth roughly one billion dollars and more than six thousand jobs. Nor was there anything simple or funny about changes in property values, comfort, and quality of life for those people who lived and worked near a swine operation.
The Swine Odor Task Force was formed in 1993 because the North Carolina General Assembly and North Carolina State University recognized that the problem of swine odors was both complex and serious. Mainly, the charge was to answer a pair of broad questions:
How can those odors be reduced or made less offensive?
This report is a summary of our response. It condenses hundreds of pages of information about growth in the swine industry, the corresponding rise in public conflicts, the sources and causes of odors, and a wide range of research topics related to waste management, water quality, and odor. Finally, the report presents a set of practical options for reducing swine odors, now and in the future.
In the interest of communication, we have tried to avoid the use of citations and highly technical language. We would like to acknowledge, however, that this report draws upon the carefully documented studies of hundreds of scientists working on several continents and in many different disciplines. Thanks in part to those scientists'efforts, North Carolina can begin taking sound, rational steps to resolve some of the issues surrounding swine odors.
North Carolina's Swine Industry
rapid gains and growing pains
Almost overnight, North Carolina acquired a billion-dollar industry that leads the nation in its rate of growth. This new industry was not built around a microchip, and it did not arrive with great fanfare. But it was thoroughly modern, based upon advanced technologies, intensive management, and scientific expertise. And it has had more impact on the state's economy than any other new industry in recent times.
It is beyond the scope of this report to tell the whole, remarkable story of North Carolina's swine industry. But to address the problem of swine odors, it will be helpful first to understand, in general terms, the industry itself--why it is the way it is.
Economic Clout in Rural Counties
Even to midwesterners, the numbers are impressive. In 1994, North Carolina had a total inventory of 7 million pigs. Gross farm income from swine is expected to reach $1.2 billion during 1995, surpassing broilers and tobacco to become the state's number-one money maker. At the current rate of growth--about 15 percent more hogs produced annually since 1990--the swine inventory could exceed 9 million head and gross farm income could reach $1.6 billion by the end of 1996.
Production has grown most rapidly in the rural counties of eastern North Carolina, where land, water, and labor are plentiful and the climate is mild. More than 90 percent of North Carolina's hogs are raised in 32 counties, primarily in the coastal plain and tidewater regions. Nine counties in the coastal plain and one in the northern piedmont produce about 65 percent of the pigs grown. Duplin and Sampson Counties, the state's leaders, together have an inventory of 2.2 million pigs--roughly 16 pigs for every person living in those counties.
The Advantages of Size
Like most modern businesses, swine operations thrive by specializing and by intensifying production. In North Carolina, about 86 percent of all swine production occurs in large, intensively managed facilities having at least 2,000 head. While some 6,200 North Carolina farms still maintain fewer than 100 pigs, these farms account for only about 5.5 percent of the state's total inventory.
Virtually all of the growth in North Carolina's swine industry in the last several years has occurred in operations having at least 1,000 pigs. Declines in the price of pork have made it difficult for producers with small herds to compete. Between 1981 and 1994, most of the 25,000 North Carolina farms that quit keeping pigs were farms with fewer than a dozen head.
Large operations benefit from economies of scale, especially in expenditures for labor, feed, and facilities. While some big farms continue to include the full range of production, from farrow to finish, these are no longer the norm. Most frequently in new operations, several specialized farms are linked or "horizontally integrated" into a chain of production and marketing. Pigs begin in sowherds on one farm, move to a nursery on another, and then move again to a grow-out farm for finishing. As each operation specializes, it takes advantage of skilled labor, expertise, advanced technologies, streamlined management and modern housing.
In North Carolina, this system typically operates under a production contract. Most such contracts make the grower responsible for providing facilities, labor, utilities, waste disposal, land, and water. The contractor provides feed, livestock, veterinary care and medicine, and managerial support. The contractor also markets the hogs, bearing all market risks and losses, and keeping any profits. Contracts typically cover one year and are calculated to pay growers a small profit for average performance. Incentive clauses provide larger profits for superior productivity.
By linking producers together into large, cooperating business units, the contracting system improves access to markets, spreads financial risk, and increases buying power. Because a similar system has been used in the broiler industry, North Carolina's swine producers and lenders are familiar with production contracts and have accepted them readily. Frequently, producers are able to debt finance as much as 70 percent of their capital investment, and many have achieved very high rates of return.
Why North Carolina?
Even as the nationwide inventory of hogs declined slightly in 1993, hog production in North Carolina continued its explosive growth. The simple explanation is that pigs have been profitable. People have made money with them. Many factors contribute to this profitability. Some of the main ones are outlined below.
1. Efficiency and productivity. Economies of scale and the use of specialized, multi-site production systems have enabled North Carolina farmers to reduce costs and maximize productivity. North Carolina producers routinely average nearly 17 pigs per breeding animal per year. The U.S. average is about 14. Feed conversion rates are also very high. In North Carolina, it takes about three pounds of feed to grow a pound of hog. Elsewhere, the ratios average three and one-half to four pounds of feed for each pound of hog. This means that North Carolina producers add weight to their hogs far more economically than do their counterparts in the Midwest, even though North Carolina producers typically pay forty to fifty cents more for a bushel of corn.
The total average economic cost of a North Carolina hog ready for market is estimated at $38 to $40/cwt liveweight or less (about 38 to 40 cents per pound). This average hog weighs about 240 pounds and was bringing an average market price of $45.00/cwt liveweight until late 1994, when prices fell sharply.
2. Markets and packing capacity. The East Coast is an enormous market for pork products delivered fresh overnight. And North Carolina's top producers have successfully developed networks to exploit this market.
Most North Carolina hogs are purchased by two packers. While less than 10 percent of the state's hog production is "vertically integrated" (owned by the packer), as much as 80 percent is closely coordinated, either through marketing contracts or verbal agreements, and most large operations deliver hogs directly to the packing plants. Both of the major packing companies continue to operate a string of buying stations for producers shipping small lots.
East Coast packers are very competitive with their counterparts in the Midwest, primarily because of shorter distances to retail markets, lower costs, and a steady supply of hogs. As a result, packing capacity on the East Coast continues to increase, especially in North Carolina and southeastern Virginia. In 1992, Smithfield Foods opened a new plant in North Carolina with a total capacity estimated at 31,000 head per day. The size and proximity of such packing operations have been major factors in the growth of North Carolina's swine industry.
3. Regulatory climate. Unlike some states, North Carolina has not outlawed or significantly restricted corporate farming. And, even though the state recently has strengthened its water-quality regulations, producers are not excessively burdened with lengthy permitting procedures. It is illegal to discharge waste from livestock operations into surface waters without a permit, and producers must now file a certified waste-management plan before building or expanding their operations. The USDA Natural Resources Conservation Service (formerly the Soil Conservation Service) assists with the design of lagoons. The North Carolina Cooperative Extension Service provides educational assistance on nutrient management in waste-treatment systems.
4. Leadership. Leadership for the swine industry primarily has come from two sources: entrepreneurs in the swine industry and expertise in the land-grant university. Industry leaders, many of whom began with small-scale family farms, have aggressively developed the commercial potential of new technologies. Many of these new technologies have evolved from an interaction of integrators, agribusinesses, and the university. Industry leaders also have provided the financial, managerial, and physical infrastructure to produce large numbers of pigs efficiently and consistently.
At the same time, North Carolina State University (NCSU) has supported the industry with its research, teaching, and extension programs. As early as 1960, the College of Agriculture and Life Sciences recognized that farmers would need new enterprises to replace tobacco income. Swine were profitable and could be produced on the small farms common in North Carolina. Over the next three decades, NCSU assembled a nationally prominent faculty in swine husbandry research, teaching, and extension. The university also established the Swine Development Center, a commercial farrow-to-finish demonstration farm, and other programs that provided a base of information and new technology. Systems developed at NCSU set standards for waste management and swine housing nationally.
Another factor is widely discussed but more difficult to document: The swine industry could adapt new technologies and production strategies because North Carolina farmers were not already heavily invested in older kinds of production systems. While hogs traditionally had been raised on many North Carolina farms, these were kept mainly in small numbers for local consumption. Many of the new large farms have achieved high rates of efficiency with state-of-the-art facilities and management.
Jobs, Investment, and Revenue
It is estimated that in 1993 the equivalent of 4,322 full-time workers were employed in producing hogs in North Carolina. Since many of those who work in swine production do so part-time, the actual number of people employed in the industry is higher than the 4,322 full-time equivalents. Another 6,750 full-time jobs existed in North Carolina in 1993 due to multiplier effects of swine production. In addition, an estimated 5,843 full-time jobs existed in pork packing and processing in North Carolina in 1993, and 8,015 more North Carolina jobs were created by the multiplier effects of the pork packers and processors. Total employment in North Carolina due to hog production and pork packing and processing in 1993 is estimated at 24,899. Employment has risen substantially since 1993 as hog inventories and processing capacity have risen.
In North Carolina, swine production requires an investment of about $1,400 to $1,700 per sow capacity, farrow to finish. It is not uncommon for a modern swine farm to have more than $1 million invested in facilities alone, and the statewide investment in facilities is estimated at $540 million. It is estimated that swine producers paid $2.2 million in property taxes in 1993. Based on inventory growth, swine producers' property-tax payments are estimated at $2.8 million in 1994 and $3.9 million in 1995. Large investments in feed mills, trucks, and pork packing and processing plants in North Carolina result in additional property tax revenues.
The boom in swine production comes at a time when eastern North Carolina's primary cash crop, tobacco, is in transition. For some farmers and many rural communities, swine production has helped offset the loss of income from tobacco. Many family farms have remained in operation by supplementing their income as contract growers or small-scale producers of hogs.
It is unrealistic, however, to expect that all of the state's small independent producers will remain competitive over the long term. During the second half of 1994, declining prices for pork severely tested the staying power of most pork producers, including many marginal and small-scale operations. While it is too early to forecast all of the implications of this trend, it is generally clear that market forces are favoring large-scale operations.
Overall, however, there are no signs that North Carolina's swine industry will be losing any ground long-term. Indeed, national trends all seem to point in the same direction: swine agriculture in North Carolina will continue to grow. But like the hogs themselves, it will grow leaner.
Large Herds, Large Amounts of Waste
As economic pressures have pushed stocking densities higher, some undesirable side effects have emerged. Large, concentrated herds generate large amounts of manure, urine, and dead animals in a relatively small area. In 1993, 590,000 sows and 10 million top hogs produced 9 million tons of fresh manure.
This amount of swine manure contains 52,500 tons of nitrogen, 40,000 tons of phosphorus (P2O5), and 37,000 tons of potassium (K2O), as well as significant amounts of other nutrients. As a practical illustration, 11.5 million tons of manure would provide for a one-inch application on 100,000 acres. That amount of untreated manure also would annually provide all of the fertilizer needs for North Carolina's six largest agricultural counties: Johnston, Sampson, Pitt, Wilson, Nash, and Robeson.
While manure is a good source of nutrients, it is a wet, bulky, difficult product to manage. Producers must regularly collect, store, handle, treat, transport, and apply the manure. Each of these activities costs the producer a substantial amount of time, equipment, and money. And each activity can release odor--if it is not properly managed. In the next chapter, we will examine the nature of swine odor, and how people respond.
The Complexities of Swine Odor
and how people respond
When we notice an odor from a swine operation, our noses have detected a complex mixture of gases, vapors, and dust. Often, this odorous mixture results as animal manures decompose anaerobically--that is, when they are slowly degraded by bacteria that do not use oxygen. The familiar smell of ammonia and the "rotten egg" odor of hydrogen sulfide gas can both result from anaerobic decomposition.
But the same anaerobic process also releases volatile fatty acids, whose odors people often find more offensive than either ammonia or hydrogen sulfide. In fact, some 150 volatile compounds have been found in swine waste. These compounds result from natural, biological reactions and include organic acids, alcohols, aldehydes, fixed gases, carbonyls, esters, amines, sulphides, mercaptans, and nitrogen heterocycles.
Many of these compounds are carried by airborne dust and other particles, some of which, in the confines of a swine house, may also contain pathogens or physical irritants. Odorous mixtures vary with location, the size and type of swine operation, production practices, season, temperature, humidity, time of day, and wind speed and direction. With so many compounds and environmental variables, it is often difficult to determine which compound--or combination of compounds--is giving offense.
To complicate matters further, our sensitivities and reactions to odors are, like fingerprints--individual and specific. They are influenced by personal preferences, opinions, experiences, and the varying sensitivities of our olfactory systems. In this way, odor is something like sound: What some people hear as music, other people hear as noise.
Whether people think of the odor as music or noise, many of those who live or work near a swine operation would like to turn the volume down. Odors can irritate, anger, or upset us, especially if we associate them with something threatening, unpleasant, or beyond our control.
In this chapter, we will examine some of the issues that have propelled the subject of swine odors into the public arena.
Sources of Odors
In general, the best odor-control system is a well-managed farm. But many parts of the swine farm produce odors if they are not well-managed and clean.
Typically, odors from swine operations originate from one or more of the following sources:
1. Buildings and holding facilities. If manure accumulates in swine houses or holding facilities, anaerobic decomposition begins and odors intensify. In open lots, uncontained odors from accumulated manure become intense during warm, wet weather. Buildings may also release odors, however, if manure builds up inside. As animals become dirty with urine, manure, and feed dust, their body heat radiates odor. Slatted floors can help separate the animals from manure and urine, but under-floor areas also generate odors unless they are frequently cleaned. There is evidence that collecting and storing manure in water, as in pit-recharge systems, reduces levels of ammonia and hydrogen sulfide gas in livestock buildings. Even so, these systems can release odors as the contents of uncovered pits and tanks are disturbed during pumping and flushing. Every part of a facility's waste-handling system produces odors if it is not kept clean.
Many of the volatile fatty acids and other compounds associated with odor attach themselves to dust. When dust from feed, dander, and other sources is allowed to coat animals, walls, and ventilation systems, virtually every surface releases odors. In a poorly ventilated building, these odors build up, and they may escape in a concentrated dose.
2. Manure storage and treatment. In North Carolina, most animal wastes are flushed, washed, pumped, scraped, or otherwise removed from swine buildings, usually with water, and stored in lagoons. If lagoons are mature, large enough, and well-managed, offensive odors will be reduced. During the startup phase, which may last a year or more, some offensive odors will be generated until materials and biological processes stabilize. Even in mature lagoons, odors are released if raw wastes are added too rapidly or if a spring warming creates a thermal inversion, lifting material from the deepest strata toward the surface. Lagoon liquid used to flush pits or irrigate land releases a relatively mild odor if it is drawn from the uppermost, aerobic layer of the lagoon. But if pumping disturbs the deeper, anaerobic layers of a lagoon, offensive odors will result.
Manure can also be stored as a liquid in concrete or metal tanks, open or covered, and in earthen storage and treatment basins. Without careful design and management, each of these systems generates odors.
3. Land application. Typically, lagoon liquids are removed from lagoons during warm weather when they can be used to fertilize pastures, forests, or crops. But these are the same seasons when heat and humidity can promote the production of odor. If liquids drawn from lagoons have received adequate treatment, odor is not usually a problem during and after irrigation.
Because sludges generally remain in the lagoon for long-term storage and treatment, they are applied to land very infrequently. But when anaerobic sludges are spread across a field, odorous compounds may volatilize rapidly. Until the materials are dry and stable, volatiles rise and move off-site in the wind. Odors usually subside in one to three days, unless humidity is high or the layer of sludge is too thick. If the material is applied in a thin, even layer during dry, breezy weather and early in the day (between 8 a.m. and 2 p.m.), much of it will dry before humidities increase during the late afternoon and evening. On some sites, land application can be managed so that the fields are downwind from nearby neighbors. Sludges and liquids may also be injected or incorporated into the soil--an effective but costly alternative to conventional methods.
4. Carcass disposal. A 1,000-sow farrow-to-finish operation may produce over 40,000 pounds of dead pigs annually. In North Carolina, most carcasses are disposed of by landfill, on-farm burial, rendering, or incineration. Decaying carcasses can release offensive odors if they are stored too long for disposal or pickup, or when they are transported. Each of the available options for disposal is problematic. Fees and restrictions on the use of landfills for animal disposal have increased so rapidly that this option is becoming infeasible. Incineration is costly in the equipment, fuel, and maintenance necessary to prevent odor and air pollution. On-site collection and burial presents the risk of disease and may threaten water quality, especially in nutrient-sensitive watersheds and in permeable soils near water supplies. In addition, disposal practices other than rendering do not allow for any recovery or reuse of the carcass as a nutrient resource. The swine industry needs new options for disposal. (See page 54 for a discussion of one possible option.)
Measures and Thresholds
If we assume that eliminating all odors from swine operations is neither practical nor necessary, we are left with a difficult question: How much odor is too much?
Recent research indicates that odors outside North Carolina swine farms are intermittent and often may result from barely detectable levels of compounds--often in the parts-per-billion range. Even so, the human nose is very sensitive, and an odorous compound does not have to be very strong to raise an objection.
The extreme variability of sources, causes, environmental factors, and human response makes it difficult to measure swine odors or determine some objective limit for odor emissions. The problem is compounded by the fact that an odor's offensiveness does not always correspond to its intensity. For instance, odors produced by agitating anaerobic slurries have been judged very offensive, even at low intensities, while odors ventilated from swine houses have been judged less offensive, even at much higher concentrations.
Despite these complications, measures and thresholds are possible and necessary, especially for odor monitoring and correction. In the effort to improve facilities and management practices, measures enable experts to establish goals and bases of comparison. By using gas chromatography and other sophisticated analytical techniques, it is possible to identify many of the various chemical constituents in an odor sample. The problem arises when we attempt to determine which of those chemicals, acting alone or in combination with one or more other chemicals, is actually causing the odor we smell.
While no standard method has yet been developed for measuring and evaluating swine odors, several techniques have been used to evaluate odors from various kinds of livestock facilities. Because the human nose is the best available odor-detector, most of these techniques involve human panels. Panels evaluating the intensity of an odor typically assign numbers to odors in relationship to their magnitude. Panels ranking odors for their offensiveness usually do so using a numerical scale.
Several devices have been used to contain an odor and present it to a panel. The simplest of these uses a cotton swatch. More elaborate tests use instruments such s the scentometer and the olfactometer, both of which dilute pungent air with odor-free air, and the different dilutions are evaluated by the odor panel. A concentration of odorants that can be detected by observers is called the "detection threshold."
Each of the methods for assessing odors is expensive and time consuming. Commercially available olfactometers can cost between $15,000 and $40,000. An odor panel using these instruments should include five or more people, each of whom must be selected, trained, and compensated. Such panels may be best suited for helping set the thresholds of certain odorous compounds, or for calibrating the instruments used in odor measurement. But panels may be too costly for use in routine testing and monitoring.
While no single method or technology is likely to account for all of the variables affecting our response to an odor, objective measures are nevertheless useful. With them, the swine industry would be able to respond to clear standards, design better facilities, and improve management practices. (For more about research and development in odor measurement and evaluation, see Chapter 4).
Perception of Odor
Without objective measures, complaints are the primary indicators that odors are a problem. But validating complaints is problematic. Perceptions of odor vary from person to person, and it is not yet clear why people feel that some odors are worse than others. For some of us, the mere presence of a detectable odor--no matter how slight--will constitute a problem.
The systematic study of odor's relation to human behavior has only begun. Even so, studies have shown that several conditions govern our perception of odor:
1. Control. We are better able to cope with an objectionable odor if we believe we can do something about it. If we feel, for instance, that a swine farm has been located nearby without our consent and without regard for our comfort or property values, we are more likely to find its odors offensive.
2. Understanding. In many cases, we can tolerate a problem better if we understand its source. Intensive livestock operations can seem alien and threatening to those who do not understand how they work.
3. Context. We react as much to the context of an odor as we do to the odor itself. For instance, some of us would rather smell the odors from cows and horses than those from other animals. In these preferences, imagination, cultural associations, and visual images seem to play a role. If we are inclined to associate pigs and swine farms with ugliness and filth, we are more likely to find their odors offensive. Also, attempting to mask a strong odor may actually amplify the perception that an odor problem exists.
4. Exposure. When we are constantly exposed to an odor, our awareness of it may eventually become blunted. In time, we may even lose the ability to detect the odor. This is one reason why people who work on swine farms sometimes wonder why their neighbors are upset about odor.
Applying these principles, we can reasonably predict that complaints are most likely to occur when new farms locate in areas where people are unfamiliar with animal agriculture--especially if people feel powerless to influence the choice of site, the appearance and upkeep of the facilities, or the amount of allowable odor.
Odors and Mental Health
In some North Carolina communities, people are upset or angry about the presence of swine operations. In public meetings and statements to the news media, some have complained about a number of actual or anticipated problems, including:
Given the emotions and personal investment at stake in such issues, it is not surprising to learn that living near a swine operation can affect mental health.
Independent of the task force, researchers from Duke University have studied the moods of people exposed to odors from commercial swine operations in North Carolina. Forty-four neighbors of hog operations and 44 control subjects participated. The study's main finding was that the mood of experimental subjects, as determined by their scores on questionnaires, was significantly impaired. In comparison with a control group, experimental subjects had less vigor and were significantly more tense, depressed, angry, fatigued, and confused. These findings are consistent with similar studies of nuisance odors in the environment.
At the very dilute levels found outside swine facilities, it is highly improbable that odorous compounds from swine operations are toxic to humans. However, because exposure to other kinds of volatile organic compounds has been shown to influence immune response, more research is needed to evaluate the implications for human health.
Understanding how individuals respond to odor helps us understand the public reaction of groups who oppose swine operations in their communities. While there are no data indicating how many North Carolinians consider swine farms to be a nuisance, protests have been so numerous and well publicized that public officials have begun to consider regulatory action.
Social scientists tell us that this public response is similar in many ways to the controversies raised by the siting of landfills, hazardous-waste incinerators, and nuclear power plants. The first public reaction is often a very emphatic "not in my back yard." Locally unpopular facilities can inspire people to mobilize into highly organized, vocal, and politically active groups.
The first objections of such groups generally focus on the mutual concerns of individuals: property values, comfort, health and welfare, aesthetic amenities, and other quality-of-life issues. But at the community level, a second set of objections develops. Civic groups and business leaders sometimes contend that a swine facility will discourage other kinds of economic development--especially those projects sensitive to odor and aesthetics, such as retirement communities and tourism and recreation businesses. These groups have also argued that new industries may not locate in a community if they feel their employees will have to live or work in neighborhoods that are smelly, unattractive, or unhealthful.
In many cases, better information can help clarify questions of risk. Economic studies, for instance, can assess changes in property values and predict the financial impact of proposed regulations. And surveys conducted by social scientists can help clarify attitudes and assumptions on all sides of a swine-odor controversy.
But for each of the issues under contention, there are serious, reasoned disagreements--even among experts. And in this regard, the swine-odors controversy resembles many other modern conflicts: In disagreements over risk, both sides often rely upon technical experts to support their points of view. But while some aspects of risk perception may be technical in nature, many others involve values and beliefs. In general, people tend to size up risks intuitively, and may be suspicious of arguments limited to technical information alone.
In these intuitive judgments, perceptions of risk are influenced by many of the same factors that influence our perceptions of odor. A risk may seem greater if it seems unfair or involuntary, if we have no control over it, or if we do not understand the source. For instance, we may feel that risks associated with odor are especially unfair if we live near a swine farm but do not benefit from its operation.
Despite the complexities of odor, risk, and perception, there is a tendency for public debates and media reports to simplify the issues into "them-or-us" oppositions. In this atmosphere, people who feel they have no power as individuals and no recourse through government sometimes become frustrated and angry. Open communication may help relieve tension and promote better policies--if the communication engages all parties equally and airs each issue on its merits.
Swine Odors and the Law
North Carolina does not directly regulate swine odors under any state or federal statute. While occupational safety and health regulations do limit the exposure of workers to some odorous gases such as ammonia, the regulations do not cover the odors detected by neighbors.
House Bill 1159, introduced in the 1993 session of the North Carolina General Assembly, sought to deal with the odors issue by mandating that intensive swine operations be situated a substantial distance from neighboring property. This proposal avoided the technical problems of measurement and monitoring of odors, but its opponents argued that the bill would impose costs that could eliminate swine production as a viable enterprise in the state.
Local governments in North Carolina cannot regulate swine production through zoning because section 153A-340 of the North Carolina General Statutes (NCGS) prohibits zoning regulations that affect "bona fide farms." However, local governments do have the general authority to enact ordinances that promote and protect the health, safety, and welfare of citizens. Using this authority, one health board has restricted swine production--a controversial step that may be subject to legal challenges.
ne-odor issues have led to litigation in North Carolina, the primary legal claim has been based on the common-law doctrine of nuisance. To support a nuisance claim, the challenged use must be "unreasonable" and must cause some "material" harm that exceeds the lesser annoyances people living in society are expected to endure.
Under this doctrine, a land use may be found to be unreasonable even though it is legal. The issues of unreasonableness and material harm must be decided by the judge or jury, who consider the facts of each case, including
If a use is found at trial to be a nuisance, the two remedies are monetary damages, which are automatically available, and an injunction, which is not. When awarding damages for a nuisance, the judge or jury puts a dollar value on the harm the neighbor has suffered and will suffer in the future. A court-ordered injunction is a more drastic remedy than monetary damages, because it can shut an operation down or force it to change. Usually, injunctions are granted only if the challenged use is highly unreasonable or if the neighbors are suffering great harm that can not be compensated with money.
The nature of nuisance law makes any litigation expensive and uncertain for both sides. Cases may last for several years, and costs usually include legal fees as well as fees for expert witnesses. These expert witnesses are used by both parties to support or refute the issues of unreasonableness and damage.
Under the nuisance statute, a previously existing legal use can become a nuisance as a result of changes in the locality. This was a concern for farmers, especially where residential development was spreading into rural areas. North Carolina's right-to-farm law, NCGS section 106-700,701, establishes that no agricultural operation (including all crop, livestock, or poultry producers) in existence for more than a year can become a nuisance because of changed conditions in the locality. The law also prevents local governments from enacting ordinances that would classify agricultural uses as nuisances.
The right-to-farm law has played only a small part in the swine-odor issue, however. The law does not protect new operations or those which create a nuisance out of negligence or improper operating procedures. In addition, producers must still comply with all applicable regulations, including those covering water quality and worker safety.
Odor and the Bottom Line
what the producers have at stake
The public debate about swine odors often overlooks a significant fact: Most swine producers have strong incentives for reducing odor. No producer welcomes lawsuits and costly new regulations. And no operation can afford to ignore the health of its workers and livestock.
This risk to health is relevant to the swine-odors issue because the odors escaping a swine farm relate directly to the air quality inside. Inside a swine house, odorous compounds at high concentrations have been found to endanger workers and animals, or damage equipment.
In this chapter, we will consider each of these factors in turn. We will outline the business aspects of waste management and odor control. And we will summarize the results of a study of waste-management practices and attitudes among swine operations in North Carolina.
Hazards for Workers
In poorly ventilated swine buildings, workers may be exposed to a number of hazards. These include harmful levels of gases, dust, infectious agents, and airborne bacteria. The most common and serious problems are gases and dusts.
Gases. In swine houses, these generally include ammonia, methane, hydrogen sulfide, and carbon monoxide--each of which affects the lungs. Most of these gases result from the decay of fecal material or the emissions of unvented space heaters. In people and pigs, gases may irritate the mucus membranes, and exposure to high levels may lead to pulmonary edema and death. Chronic exposure to low levels of swine-house gases may lead to airway inflammation and a decrease in lung function.
Around manure pits, a very serious hazard is hydrogen sulfide gas. At low concentrations, this gas is identifiable by its "rotten egg" odor. At high concentrations, hydrogen sulfide gas may be undetectable by smell and can cause instant respiratory arrest and death. Several people in the midwestern United States have been killed or critically injured by exposure to hydrogen sulfide after the agitation of liquid manure in the deep pits that are common there.
Dusts. Agricultural dusts contain molds, bacteria, insect parts, pollen, grain particles, mineral ash, animal feed, animal fluid, dander, and excreta. About a quarter of this dust is usually composed of proteins, some of which can become allergenic. Barn dusts also tend to be very fine, and as much as half of their contents may be respirable, taken deeply into the lungs. Long-term exposure to such dusts has been found to cause respiratory damage. And there is also a short-term effect. Studies have shown that when respirable dust exceeds a threshold of 0.23 milligrams per cubic meter, a worker's lung function decreases significantly over the course of a workday.
Symptoms. Because some chronic health problems may resemble such common ailments as flu or smoker's cough, the effects of poor air quality on workers in swine buildings may have been underestimated. Conditions noted in some workers at confined-animal facilities have included hydrogen sulfide poisoning, bronchitis, hyperactive airways disease, atopic asthma, acute organic dust toxic syndrome, chronic organic dust toxic syndrome, mucous membrane irritation, increased susceptibility to other chest illnesses, chronic sinusitis, a byssinosis-like condition, nausea, diarrhea, rhinitis, fatigue, eye and throat irritation, headache, shortness of breath, wheezing, dizziness, and sleep disturbances.
Regulation. Swine operations with more than 10 employees at any time of the year must comply with safety and health standards set by the U.S. Occupational Safety and Health Administration (OSHA). Currently, the most applicable health regulation is OSHA's Hazard Communication standard. Under this standard, workers exposed to significant amounts of a hazardous compound must be trained about its toxic properties and taught how to protect themselves. Portions of the Hazard Communication regulation also apply to the use and mixing of feed materials and supplements. In addition, the standard requires employers to label hazardous materials and their containers, and to develop information sheets about the hazardous compounds present, including safety measures for workers.
OSHA's regulations limiting exposures to hazardous chemicals have not yet been applied to agriculture. These regulations, called Permissible Exposure Limits (PELS), apply now to general industry and construction. They set specific exposure limits for about 600 compounds, including hydrogen sulfide, carbon monoxide, ammonia, and methane. Workers exposed beyond these limits are required to use respirators or take other protective measures. Currently, OSHA is considering applying PELs to agriculture. If it does so, the agency will first hold public hearings, and the process will probably take one or two years.
Hazards for Animals
Most of the gases and other air-quality problems that endanger the health of workers also are hazardous to pigs. Air pollutants in swine buildings may weaken the respiratory tract and predispose animals to disease. In high concentrations, dusts and gases may also affect reproduction, piglet survival, and growth. The most common sources of air-quality problems are described below.
Hydrogen sulfide. There are many reports from the Midwest of pigs dying from the sudden release of hydrogen sulfide from liquid manure that has been agitated. Animals exposed to sub-lethal doses may become more susceptible to pneumonia and respiratory diseases, and pigs exposed continuously to 20 ppm (parts per million) of hydrogen sulfide develop photophobia, anorexia, and nervousness. With adequate ventilation and care in the handling of manure, hydrogen sulfide can be maintained at levels that do not exceed 20 ppm.
Ammonia. This is the most common noxious gas in animal buildings. Under some conditions, this irritant can cause permanent tissue damage in confined animals. It is rarely found in lethal concentrations (greater than 3,000 ppm) in animal houses. While the current standard for safe ammonia levels is 25 ppm, recent research indicates that maintaining a level of no more than 10 ppm may help prevent health risks in pigs and humans alike.
Dust. Dust in confinement buildings presents many of the same hazards for animals as it does for humans. Evidence indicates that some dusts irritate or inflame lung tissues, lower the animal's resistance to respiratory illness, and contribute to the causes of disease. Dust particles are effective carriers of pathogenic microorganisms, and some smaller particles also adsorb and carry gases such as ammonia deep into the lungs.
Carbon monoxide. Most cases of carbon monoxide poisoning have been linked to improperly vented or malfunctioning space heaters. Deaths in adult pigs have been observed at 4,000 ppm and in chickens at 2,000 ppm. In poorly ventilated buildings, carbon monoxide levels may average 500 ppm. At levels of 200-300 ppm, growth rate in pigs may be reduced by 25 percent.
Carbon dioxide. The effects of carbon dioxide are generally less severe and shorter-lived than those for carbon monoxide. While national standards set a maximum safe level of 5,000 ppm, some scientists recommend maintaining levels below 1,500 ppm both for both humans and swine. Typical levels in swine barns range from 1,400 ppm to 5,000 ppm under normal conditions. In extreme cases, the build-up of carbon dioxide to concentrations of 100,000 ppm (10 percent) can lead to dizziness, anxiety, staggering, and unconsciousness in pigs.
Hazards for Buildings
The environment inside confinement facilities also poses a threat to the physical structure of the building and its component systems. Moisture and corrosion take a toll on the metals in truss connectors, pens, and electrical systems.
Fixtures and wiring practices that work well in people's houses will not stand up to the gases, dusts, and dampness in a swine house. Most modern swine buildings are constructed to meet electrical codes for high-moisture, corrosive environments. In some older buildings, however, fires and stray voltage can result from breakdowns in conduit and wire, creating hazards for humans and livestock alike. Failed electrical systems are responsible for most of the losses caused by fires on farms.
From the Business Manager's View
As a business manager sees it, waste-management practices used by swine producers in North Carolina are effective and relatively inexpensive compared to practices used elsewhere. Even so, these practices represent a large investment in facilities, maintenance, and operation costs:
Houses. Concrete pit and gutters, raised floors, and slats are expensive to construct, and the ventilation fans and their controls are costly to install and operate. Construction costs for a heavily ventilated building with slatted floors may be $110 per space for a finishing hog, while the same space in a solid floored building may cost $65.
Lagoons. Lagoon construction costs are estimated at $1 per cubic yard and may amount to $4.50 per finishing space. Also, the grading and leveling required to situate a building above the lagoon add to construction expense.
Sprayfields. Producers invest substantially in sprayfield preparation and irrigation equipment, as well as in labor and pumping. Irrigation costs range from $135 to $270 per acre annually, or from $1.16 to $2.32 per space for each finishing hog.
With so much investment at stake, the business manager's approach to swine odors is to minimize conflict while maximizing future profits. Managers increase their expenditures for odor reduction if doing so helps the business avoid higher legal expenses, tougher regulations, or other costly problems. However, if the long-term costs of odor reduction will exceed the cost of relocation, the business may move to a site where odor will not be an issue. When a business seeks a new production site, it can generally afford to reject any site where the cost of managing odors will be high.
Practices and Attitudes
As they weigh the costs of public conflict, new regulation, and the hazards of odorous compounds, most livestock producers acknowledge the importance of waste-management practices. This is particularly true for swine producers, most of whom store, treat, and use virtually all of the animal wastes on the farm.
During 1994, social scientists from North Carolina State University surveyed more than a 1,000 livestock and poultry producers in the state about their waste-management practices and attitudes. More than half (55 percent) of the 410 swine producers responding stated that the potential for reducing odor was a "very important" influence on their waste-management decisions. Only one other influence--the potential to control water pollution--was cited as a very important influence by more swine producers (73 percent). Even so, most of the swine producers surveyed also felt that "public concern over animal waste is really more about odor than about water quality."
In general, swine producers seem to accept the idea that some regulation of waste management is necessary. Most (78 percent) disagreed with the statement that "producers should have the right to manage their waste in any way they choose."
At the same time, many of the producers surveyed feel that animal agriculture has received more than its share of public criticism and environmental regulation. Most (74 percent) agreed with the statement that "animal agriculture is being unfairly blamed as a cause of water pollution." Most also felt that environmental laws are becoming so strict that many farmers will have to quit raising livestock.
More than three-fourths of the swine producers surveyed are satisfied with their current waste-management practices and do not plan to change them. And most feel that they have all of the information and assistance they need.
Despite this confidence in their practices and information, many of the swine producers surveyed have not yet adopted some of the "best-management practices" and other measures currently recommended for storing, treating, and applying wastes. Of the swine producers who apply their wastes to land (63 percent), only 49 percent have calibrated their equipment in the last five years. And 40 percent have tested the wastes for nutrients in the last five years.
Perhaps the most significant finding of this study is the striking contrast between the responses of small-scale producers and those of large-scale producers. Of those swine producers having more than 1,000 animals, 75 percent reported having a written waste-management plan (now required for large operations). Only 10 percent of those with fewer than 250 animals had completed such a plan. (Producers with herds less than 250 head are not now required to file waste-management plans.) While 56 percent of the producers with more than 1,000 animals had tested their swine wastes for nutrients, only 18 percent of those with fewer than 250 animals had done so.
Producers with large-scale operations also tended to accept regulation as practical and necessary. Of those with more than 1,000 animals, only 9 percent agreed that "Growers should have the right to manage waste in any way they choose." In comparison, 36 percent of those producers with fewer than 250 animals agreed with the statement.
There are several factors that may account for these differences in attitudes and practices. Larger operations are more likely to have the technical staff and capital necessary to adopt new technologies and implement waste-management plans. Also, most of the largest operations in North Carolina are relatively new, and many have benefitted from recent advances in management practices and building design.
Among all of the livestock and poultry producers surveyed, dairy producers as a group seem to be the most advanced in their waste-management efforts. This may be due to the fact that dairies traditionally have been closely regulated. Because milk itself is produced on the dairy farm, public health agencies and the dairy industry have long recognized the relationship between cleanliness on the farm and the safety and quality of dairy products.
In commercial swine production, no edible product is actually derived until the animals have left the farm. Therefore, cleanliness in swine houses has not generally been assumed to relate directly to the quality of pork as a product. While there is some preliminary evidence that odorous compounds in swine houses may affect the quality of pork, it is not yet clear how significant a factor this might be.
A Role for New Technologies
As we will see in the next chapter, stringent regulations in several European countries have, in some cases, led to waste-management and odor-control systems more advanced and elaborate than those in the U.S. But in Europe, producers generally recoup the cost of those systems in the higher prices paid for pork. In some parts of the world, then, society has been willing to pay more for its food in order to ensure cleaner water and air.
Of course, waste-management issues in Western Europe are very different from those in North Carolina. In the Netherlands, for instance, the average population density is 868 people per square mile. In North Carolina, the average density is 141 people per square mile, with only 50 people per square mile in Sampson and Duplin Counties. And it is not certain that countries like the Netherlands will be able to sustain their current levels of swine production. Under the new General Agreement on Tariffs and Trade (GATT), which is likely to increase trade with Eastern Europe, pork production may decrease sharply in densely populated, highly regulated regions of Europe.
In the U.S., producers already compete in open markets where profit margins are slender and the price for pork is--by international standards--very low. From the business manager's vantage point, adopting a new technology or practice will make sense only if doing so reduces costs or risks, making the business more competitive.
But producers are not the only group with an interest in keeping costs low. Consumers have an interest, as well. And law-makers generally are becoming more and more reluctant to impose regulations that restrict economic growth, increase the cost of living, and increase the cost of government.
For each sector, then--industry, consumers, and government--there is a mutual interest in the development of cost-effective new technologies for reducing odor. And the benefits of these technologies are likely to extend beyond odor reduction alone. Since most agricultural odor problems are also waste-management problems, their solutions are likely to affect not only odor but water quality, energy conservation, and nutrient management as well. In the next chapter, we will examine some of the technologies and research initiatives that seem to hold promise for North Carolina.
The Search for Solutions
research and promising technologies
As the Swine Odor Task Force sought new methods for reducing odors, we concentrated on two places known for their innovation: North Carolina and Western Europe.
North Carolina has for many years been a national leader in research and technology for swine production and waste management. Many of the practices considered standards for the swine industry have been developed here, mainly by business leaders and by scientists and educators at North Carolina State University.
In Western Europe, stringent regulations have accelerated the development of technologies for protecting the environment in a region that is very densely populated, both with people and with animals. In the Netherlands, for instance, 90 percent of acid rain results from ammonia, and some of this ammonia results from animal agriculture.
Primarily because of concerns about acid rain and water quality, legislation in the Netherlands has required a reduction of ammonia emissions to 50 percent of 1980 rates by the year 2000 and by 70 percent by the year 2010. In response, industry and government have, since the 1970s, invested in research and new technologies for protecting air and water quality. As a result, agriculture has reduced not only ammonia but other odorous compounds as well.
To learn from these advances, several representatives of NCSU in 1994 visited three European countries--the Netherlands, Germany, and Denmark. On trips to farms, industries, universities, and research institutions, the group studied the best available technologies and research related to air and water quality, energy production, and odor reduction.
We did not always find agreement, however, about the potential and practicality of the various new technologies we reviewed. For some experts, it is not yet clear, for instance, whether aerobic treatment of wastes should be recommended in preference to the less-costly anaerobic treatment. Nor is it clear when technologies for using swine wastes to produce biogas or other value-added products will become practical and profitable for use on North Carolina farms.
For scientists, disagreement on such questions is a natural and necessary aspect of progress in any rapidly developing technical field. As a group, the task force has chosen to cast a wide net, considering a great number of technologies and management options. In the sections that follow, we will briefly describe some of the most prominent of these, flagging the ideas which seem most relevant for the long-term reduction of odor in North Carolina.
Measurement of Odors
Because of the costs and variables involved in using human panels to measure odor, a number of devices have been tested for their ability to measure odors electronically. In Australia, for instance, scientists are developing an electronic device that senses para-cresol, which is sometimes regarded as an "indicator chemical" in swine odor. In general, however, research in Western Europe supports the general agreement among U.S. scientists that there are no reliable chemical indicators for odors caused by complex biological materials such as manure. In addition, odorous compounds are interactive, not additive, in their effect. That is, the combination of several odorous compounds may create a unique odor and not several odors perceived independently.
Even so, the difficulty of measuring odors has not prevented the use of thresholds and standards in Europe, and the European Economic Community is moving toward a common standardized procedure for the measurement of odor. In Germany, thresholds based on the use of olfactometers have withstood legal challenges. And in the Netherlands, ten certified laboratories apply a standardized procedure for measuring odor--at considerable cost. The Netherlands has also adopted a new "Green Label" code for environmentally friendly housing for animals. To qualify, the facility must not exceed a threshold for ammonia emissions (described above).
While ammonia is neither the only source of odor nor the most offensive, studies in Europe consistently find that measures to reduce ammonia generally do reduce odors from other compounds as well. In land application of manure, for example, reducing ammonia emissions by 100 units was found to reduce odor by 70 units. The biological sources of ammonia--the digestive byproducts of microbes--also yield other odorous compounds. Drying or acidifying animal wastes stops microbial action, preventing the production of odorous compounds. But when microbial action ceases, so does the reduction and transformation of nitrogen, so more nitrogen remains in the wastes.
Measurements at swine facilities. Two recent studies in North Carolina have focused on the measurement and characterization of odors from swine operations. The first of these studies, funded by the National Pork Producers Council, was conducted by scientists from North Carolina State University. The investigators used two commercially available instruments to measure odors at six swine facilities. Four of the facilities housed between 620 and 640 animals in each swine building and used fully slatted floors with under-floor or tunnel ventilation. The other two facilities housed 1,224 animals in each swine building and used partially slatted floors with roof ventilation. At each site, odors were monitored at locations near the ventilation fans, around houses and lagoons, and in nearby fields.
When investigators compared odors from different facilities, several trends emerged. Locations at the ventilating fans used with under-floor and tunnel systems yielded the highest levels of odor. Even so, levels measured around the buildings using these systems were generally lower than levels taken around roof-ventilated buildings. Lagoons produced levels of odor roughly comparable to those around the houses.
Key idea: In a study of six North Carolina swine facilities, odors were generally lower around buildings using under-floor or tunnel ventilation than around buildings with roof ventilation.
The study also compared the two measuring instruments:
1. The Scentometer(TM) Model SCC, manufactured by Barnebey & Sutcliff Corporation, requires the user to inhale air through two nasal inserts (one in each nostril). The user first receives odor-free air and then a sequence of increasingly odorous samples, and a threshold is established when the user first detects the odor. An odor's magnitude is determined by the number of dilutions required to reach the threshold. Like other olfactometers, this instrument relies upon the judgment of users, who vary in their responses. Users exposed to an intense odor for a long time can experience "olfactory fatigue," losing their sensitivity to the odor.
2. The Odor Monitor(TM) by Sensidyne has been used primarily to evaluate food odors and has not been widely tested in agricultural applications. Because the instrument measures odor-causing molecules and does not require a human subject, it avoids the biases caused by judgment and olfactory fatigue. But this strength also represents a limitation: The Odor Monitor is sensitive to substances that people may not detect as odorous.
Both instruments provided rapid measurements in the field. And, in general, odors were assigned about the same rank, regardless of the instrument used to measure them. There were a few exceptions to this agreement, however. Some samples causing high readings on the Odor Monitor were not detected as odorous by subjects using the Scentometer.
Key idea: Despite some limitations, two measuring instruments generally agreed on the ranking of odors at six swine facilities.
Evaluation and characterization of odors. A study by scientists at Duke University Medical Center has been evaluating and characterizing odors from 20 swine operations, each of which has been the subject of complaints about odor. At each location, air samples were collected at distances of 750 and 1,500 feet from the swine operation. The samples were presented to an odor panel, who rated odors by their intensity and characterized each sample using descriptive terms.
While the study is not yet complete, findings from its first phase have been made available for the purpose of general discussion in this report. At each of the sampling sites, odors were intermittent. Levels of odors tended to be highest during early morning and evening when air turbulence was reduced and air movement approached laminar (smooth) flow.
In most sample, odors at 750 feet downwind from the facility were very faint (three to nine times above threshold). On one occasion, however, a constant and invariable wind carried odor directly from a facility's ventilation fans to the sampling site 750 feet away. Without eddying currents to dilute and disperse the odor, levels rose to 27 times higher than threshold.
Levels of odorous compounds detected in this study were extremely low. Investigators had difficulty acquiring samples with enough molecular mass to be analyzed chemically (using a gas chromatograph and mass spectrometer). No hydrogen sulfide was detected above 0.5 ppm, the limit of the detection method. At the minute levels sampled, the odorous compounds are unlikely to be toxic to humans. However, the body can collect the odor-causing molecules in blood and fat, releasing them in the breath. As this study continues, the investigators will attempt to develop better methods for isolating and analyzing very low concentrations of volatile organic compounds.
When it comes to odor, not all swine manures are created equal. The odor-causing potential of fresh manure varies among pigs and their diets. Because nitrogen is a key ingredient of ammonia and many other odorous compounds, it is generally true that the higher the nitrogen content of swine manure the greater its potential odor.
In general, pigs excrete excess nitrogen when they ingest more protein than they can efficiently use. In some diets, amino acids are not in balance with the animal's requirements. In others, the source of protein used in the feed is poorly digested. Improving the conversion of feed can not only reduce odor but also lower feed bills, which represent about 60 percent of a swine operation's production costs.
Research on feed conversion and odor control has progressed in several directions:
1. Amino acids. In Europe, researchers have devoted much effort toward reducing the excretion of nitrogen by pigs. In most studies, this has involved substituting synthetic amino acids for traditional protein sources. Considerable research will be necessary before this approach can be further exploited in North Carolina.
2. Digestibility of protein. Studies in North Carolina and elsewhere have established that protein sources can be improved by better processing or rendering techniques. The use of proteolytic enzymes in processing or as dietary supplements can also increase protein digestibility.
3. Odor absorbers. There are numerous reports about dietary supplements such as calcium bentonite, zeolite, sagebrush, and charcoal--all of which adsorb odor-causing compounds such as ammonia. However, if these compounds are fed to pigs at the levels required for reducing odor, they may also reduce growth or the efficiency of feed conversion.
4. Sarsaponin, enzymes, and microbials. Some of the most promising feed additives are plant extracts, enzymes, and direct-fed microbials, all of which may help control odor and improve growth performance in animals. Research indicates that sarsaponin, a natural extract from the yucca plant, can reduce ammonia and promote beneficial microbial action in pits and lagoons. In some studies, mixing sarsaponin with pig feed has also increased weight gains and improved feed conversion.
It is not yet clear exactly how sarsaponin works. Some studies indicate that the compound inhibits urease or promotes microbial growth. There is also evidence that sarsaponin removes ammonia, which is toxic to many microbes, converting the ammonia nitrogen into microbial protein. Sarsaponin may condition microbial cell membranes and reduce surface tension, increasing the absorption of nutrients across cell membranes and promoting microbial growth. Because sarsaponin passes unabsorbed through the animal, it provides a simple, indirect means of treating litter or the contents of lagoons.
In addition to sarsaponin, several other supplemental enzymes, probiotics (direct-fed microbials), and bacteria may also reduce odors in swine houses. Much more research is necessary, however, to evaluate the potential and practicality of each of these kinds of additives.
Unfortunately, some additives in current use may actually increase the odor of manure. Antibiotics and certain growth promotants, such as arsenic and copper, inhibit microbes not only in the gut of the animal but also in its manure, retarding the microbial digestion of odorous compounds. This would be a concern primarily in liquid-based treatment systems.
Key idea: With further research and development, several kinds of feed additives may help improve feed conversion and reduce odor.
Many products are available for treating or preventing odors in animal facilities, manure storage tanks, and lagoons. Most of these products are found in one of the following categories:
1. Masking agents are mixtures of aromatic oils used to cover up an objectionable odor with a more desirable one.
2. Counteractants are aromatic oils that cancel or neutralize an odor so that the intensity of the mixture is less than that of it constituents.
3. Digestive deodorants contain bacteria or enzymes that eliminate odors through biochemical digestive processes. For example, sarsaponin can be added directly to lagoons, promoting microbial action.
4. Adsorbents are products with a large surface area that may be used to adsorb the odors before they are released to the environment. Sphagnum peat moss, for example, has been found to reduce odor in some lagoons.
5. Chemical deodorants are strong oxidizing agents or germicides. Germicides such as orthodichlorobenzene chlorine, formaldehyde, and paraformaldehyde alter or eliminate bacterial action responsible for odor production. Oxidizing agents such as hydrogen peroxide, potassium permanganate, and ozone chemically oxidize odor-causing compounds.
Each of these groups has its strengths and limitations. Masking agents and counteractants, for instance, can be effective in the short-term storage of wastes. But because these products typically are organic compounds that can be broken down by bacteria, most of them quickly lose their effectiveness in lagoons and tanks.
Recently, aggressive marketing has increased the use of digestive deodorants. These products, which contain enzymes or bacteria or both, are advertised for their abilities to break down solids, reduce the release of ammonia, and conserve nitrogen. No one product affects all of the odor-causing compounds possible in swine manure, however. And unless the environments of lagoons and other waste-treatment systems are favorable, supplemental bacteria may die off or fail to reach sufficient numbers to control odor. Of the many products tested in the Netherlands and in Germany for their ability to reduce odors from manure slurries, none has proven reliably effective.
Some additives reduce odor by altering the volatility of odorous compounds. Lime, for example, inactivates compounds such as hydrogen sulfide but also increases the amount of ammonia released from manure. Because of an emphasis on reducing ammonia, research in Europe has focused on acidifying agents. Studies indicate that applications of lactic acid bacteria can maintain the ph of manure at 6.4, reducing ammonia emissions by as much as 80 percent during storage and application. Because this process also retains nitrogen in the waste, there is much more nitrogen applied to land than is the case with lagoon-based systems.
Key idea: While some additives are occasionally effective, it is unlikely that any one product or procedure will eliminate swine odors. More research is needed to establish the usefulness and reliability of products.
Despite the dozens of products sold for reducing swine odors, each with testimonials and claims about its effectiveness, no standard method has been established for evaluating these products in the U.S. Even when products have been evaluated, testing conditions and results have been so variable as to yield very little reliable information.
During 1994, several members of the task force collaborated with scientists from Iowa State University, Oregon State University, three European institutions and other research organizations to develop a protocol and models for testing odor-control products. The group recommended a rigorously controlled approach including the following measures:
1. Product evaluations should first be conducted and replicated in laboratories using Good Laboratory Practice (GLP) standards to avoid the variability associated with field testing.
2. Odor should be measured with olfactometers and human panels, and should be quantified using methods of the American Society for Testing and Materials (ASTM).
3. Vendors having odor-control products tested should be required to disclose the content and composition of the product to the investigating laboratory.
4. Results should be published and made available to the swine industry.
The scientists also agreed upon a protocol, specifying testing procedures, materials, and standards at three levels: bench-scale evaluation in the laboratory, model-scale evaluation in the laboratory, and pilot-scale evaluation in the field. In addition, the team suggested administrative procedures for managing a testing program. At NCSU researchers are using these testing procedures to evaluate various products for controlling swine odors.
Key idea: Collaborating scientists have recommended a protocol for evaluating a product's ability to reduce odor.
Research and experience in Europe confirm what has become well established in North Carolina: Each of the major carriers of odor--gases, dusts, and vapors--can be controlled, but only with the right ventilation.
During winter, when buildings are closed and heated, producers sometimes hesitate to run the ventilation fans, knowing that heat will escape as the air is exhausted. But specially in winter, ventilation should be constant. A sow and litter produce about one pound of water per hour--or about three gallons a day--in the form of water vapor. Good ventilation helps to prevent condensation, dampness, mold, and the corresponding risks of disease or damage to buildings. It also prevents the buildup of noxious gases formed by the decomposition of stored manure and, in general, improves the environment for workers and pigs.
A building's design and ventilation system greatly affect the movement of particles. For example, a building using sidewall ventilation can move large volumes of air, diluting the concentration of particles inside the building as well as in the air exhausted from the building. Ventilation systems that move particles into underfloor pits tend to trap them in the liquids, where they are removed to the lagoon for treatment. (The North Carolina Cooperative Extension Service provides detailed specifications and design criteria for ventilation systems in swine buildings.)
In the European countries visited, climate and environmental regulations dictate a building design and ventilation system somewhat different from those in North Carolina. To reduce energy demands, one European system draws air through ducts buried underground. In this system, the ambient temperature of the earth warms the air in the winter and cools it in the summer. (A similar system tested in the milder climate of North Carolina did not perform well.)
In the North Carolina underslat ventilation system, air enters the building through slots and baffles that are continuous with the eaves (1), mixes with warm air before reaching the pigs, moves through the slatted floor into flush channels or manure pits (2), and is drawn through uniformly spaced openings into the plenum, from which it is exhausted. (Source: "Ventilation of Swine Buildings Using the North Carolina Underslat Ventilation System," L. Bynum Driggers. North Carolina Cooperative Extension Service, AG-132.)
With its intensive swine-production systems, North Carolina has become a net importer of nutrients. Producers bring in large amounts of grain, mostly from the Midwest, and feed it to their pigs. Not all of these nutrients leave North Carolina when the pork goest to market. Large quantities of nutrients remain in the urine and manure. Therefore, the state must absorb more nutrients that it exports, becoming a "nutrient sink." In some densely populated regions of Europe, a long history of importing livestock feed has posed severe threats to water quality by overloading the soil-plant system with more nutrients than it can use.
In previous chapters, we have described some of the waste-management systems common in North Carolina's swine industry. In general, these systems use water to flush wastes from buildings for storage in anaerobic lagoons. Most of the modern production facilities in the state typically combine pit-recharge disposal of manure with the use of under-floor ventilation--a system that produces relatively little odor when it is operated according to established guidelines. In most cases, facilities with severe odor problems are improperly managed or designed, or they include old buildings with solid floors and inadequate ventilation. Even so, the task force found a number of innovations that could, with further development, have potential for reducing odor at some locations in North Carolina.
Waste handling in the houses. Because of the emphasis on protecting water quality and preventing acid rain, research and development in Europe has focused on waste-handling systems that suppress the production and release of ammonia. In general, this has meant taking steps to promote cleanliness, to separate urine from manure, and to reduce the surface area of manure exposed to air. European systems also tend to circulate less water than do systems in the U.S. Because European producers generally must pay to have manure hauled away for treatment or disposal, reducing the volume of manure helps lower the costs.
In the Netherlands, several new designs have been developed for separating urine from manure. One includes a sloping floor with a small gutter for urine. Surfaces are coated with TeflonTM and can easily be scraped six times a day. This system was found to reduce ammonia emissions by about 60 percent over conventional Dutch systems (8.3 kg of ammonia per sow space per year). Another experimental system dries manure in place by moving it slowly over blowers using a perforated belt.
In response to regulation, the swine industry has developed several new designs for swine houses in the Netherlands. One of these is the HepaQ Environmental Pig HouseTM, created by Hendrix Feeds and the Plaques engineering firm.
In this design, slurry is flushed out of the manure pit several times a day to limit odors and reduce the need for ventilation. In the slurry tank, viscous manure settles to the bottom. From there, it is transferred into storage for processing at treatment plants or application to land. Liquids from the slurry tank are treated by aeration then recycled for use in flushing. Excess liquid is evaporated using ventilation fans and outside air.
The companies estimate reductions of 40 to 50 percent in the volume of manure, and 60 to 70 percent in the emission of ammonia, as compared to conventional Dutch systems.
Waste treatment. For several reasons, lagoons are rarely used for treating swine wastes in Europe. The relatively low amount of water produced in European systems makes lagoon treatment somewhat impractical and inefficient. In the Netherlands and Denmark, the water table is too high to accommodate manure-treatment lagoons. And, in a cold climate like Denmark's, lagoons would have to be very large to provide effective treatment. Also, Europe's environmental regulations have increased the costs of construction and operation. In Germany, for instance, regulations require that lagoons be lined, covered, and equipped with underground pipes for the detection of leaks.
But just as significantly, European producers tend to view liquid and solid wastes as separate resources that yield separate products. This approach has led to a number of technologies for treatment that are uncommon in the U.S.:
INSET: At North Carolina State University, research is under way to develop a system for composting two materials that are overabundant in eastern North Carolina: swine manure and peanut shells. Because the manure is high in nitrogen and the shells are high in carbohydrate, composting them together is expected to provide a consistent, well-balanced material of value either as a soil amendment, fertilizer, or other product. This work is based partly on long-term studies, conducted at NCSU, into the separation of liquids from solids in settling basins.
Separating liquids from manure not only simplifies treatment but also enables the development of useful products. In one European system, for instance, a two-stage separator provides a solid (consisting of 65 percent dry matter), which is composted for use as a potting medium in nurseries. The liquid fraction is used as a fertilizer in hydroponic greenhouses. In Germany, solids are often composted and marketed as fertilizers and soil amendments. This practice has produced so much compost that the supply is exceeding demand.
But in Europe, not all swine wastes are treated on the farm. At some locations, wastes are trucked at producers' expense to remote farms for direct land application. At others, agricultural wastes are trucked to central plants for treatment along with municipal or industrial sludges. Because these plants are under pressure to prevent odor and reduce the volume of wastes applied to land, several technologies have emerged over the last two decades.
In Denmark, for instance, one firm is using mechanical vapor compression to evaporate and purify water from industrial and agricultural wastewater. The system, which can separate swine wastes into dischargeable water and a concentrated, nutrient-rich slurry, is being tested for on-farm use. The company involved estimates that three forty-foot modular plants plugged into the slurry pipe of a swine facility could process 20 to 30 tons of waste per day.
Of course, each of the technologies discussed in this section has some limitations, and some may not prove to be practical for North Carolina. Also, while these technologies offer some advantages for odor control, they do not in themselves reduce the net amount of nutrients that must be managed in the system.
Key idea: Several new technologies for waste treatment reduce the volume of liquids and yield useful products.
Applying Wastes to Land
As we have discussed in previous chapters, the application of waste to land is one of several potential sources of odor on swine farms. Generally, odors are most intense during the first few hours after spreading and decrease exponentially with time, with small daily fluctuations.
A number of "best-management practices" have been recommended for the application of wastes to land in North Carolina. These practices address equipment and methods of application that can reduce odor, protect water quality, and ensure that crops can efficiently use the nutrients available in the manure. The North Carolina Cooperative Extension Service provides detailed guidelines for calculating the amount of swine manure required for use as fertilizer, and tables are available for estimating the number of acres required for various kinds of swine operations and crops.
Beyond these established recommendations, there are several additional practices that may help reduce odors from manure applied to land. Studies in Europe and Australia have found reductions in odor when solids are removed and slurries are treated aerobically (see inset, Aerobic Treatment, in Brief). But anaerobic treatment also has been found to reduce odors, if the digestion has been complete enough to break down volatile fatty acids and other odorous compounds.
Whatever the method of treatment, odors are reduced if manure slurries or lagoon sludges are injected or incorporated into the soil immediately after application. Because of the cost of this step, which requires a considerable investment in time, fuel, and equipment, most swine producers in North Carolina do not inject or incorporate manures.
Each of the European countries visited by members of the task force regulates the timing of manure-slurry applications, which typically are limited to spring and early summer when crops re growing rapidly. Several countries also regulate the locations, methods, and rates of application. In the Netherlands, the scarcity of land has led to high disposal costs and strict regulations. Producers often move their slurries great distances for treatment or application to land, paying about $30 per pig per year for disposal. Some land owners even receive payment for having manure applied to their land.
Regulations in the Netherlands require that manure be incorporated into the soil within 24 hours after spreading. During that period, equipment must be constantly at work on the site, spreading slurry or incorporating the manure. Police and other inspectors patrol land-application sites and can issue a ticket or fine for each violation. In addition, swine producers must analyze the amounts of phosphorus and nitrogen produced in animal wastes and balance them with the estimated needs of the crop on which they are applied. If a producer does not keep track of this balance using a bookkeeping system, authorities can level fines based on worst-case assumptions about nutrient loads and the treatment capacity of the land.
The task force does not recommend such stringent regulation for North Carolina, where rural land is far more abundant. But at locations where odor is a serious issue, or where run-off reaches water supplies, producers may be advised to manage nutrient balances carefully (a step required by new waste-management regulations) and inject or incorporate the manure slurries or sludges applied to land. Incorporating liquids, on the other hand, is likely to be very costly and impractical, and might actually promote soil erosion and nutrient leaching into water supplies.
INSET: Aerobic treatment uses air. Anaerobic treatment does not. Most lagoons, manure pits, and other facilities for handling swine wastes are anaerobic, because their submerged materials are not exposed to air.
Like many other natural materials, swine manure can be oxidized by bacteria that use oxygen. These bacteria efficiently transform the manure into a chemically stable material, reducing both pathogens and odor. Some of these aerobic bacteria "digest" or oxidize carbohydrates to carbon dioxide and water. Others feed on organic substances and convert nitrogen compounds to ammonium. Still others oxidize ammonium salts to nitrites then nitrates in a process called "nitrification."
For the purposes of odor control, the main advantage of aerobic treatment of wastes is that it does not produce the volatile fatty acids and various other compounds associated with very offensive odors. The main disadvantage of aerobic treatment is that it generally requires power to aerate the materials.
A number of researchers have presented evidence that treating swine waste aerobically can lessen its odor. Aeration promotes the growth of bacteria that can rapidly degrade phenol, p-cresol, volatile fatty acids, and other compounds. If the solids are first removed, slurries treated aerobically become more stable and produce less odor when they are subsequently stored and applied to land.
In North Carolina, the cost of energy required for mechanical aeration, coupled with the extra step of separating solids from liquids before treatment, has created the perception that aerobic treatment systems are not yet practical for swine production. If technologies develop and pressures for odor reduction increase, this view may change.
Key Idea: In addition to best-management practices, injecting or incorporating manure may help control odors and protect water quality in some locations.
Fermentation of Dead Animals
One of the most promising technologies for disposing of dead animals is anaerobic fermentation, a natural, biological process similar to the production of corn or grass silage. Properly managed, anaerobic fermentation can preserve carcasses on the farm for recycling into a feedstuff. The two versions of this process--one of which uses lactic acid and the other yeast--share the same basic requirements. Carcasses are ground into particles of one inch or less, and these are mixed with a fermentable carbohydrate and an acid-forming bacteria in a non-corrosive container vented to release carbon dioxide.
Under the right conditions, bacteria rapidly acidify the tissue until it is stable. The result of this process is a semi-liquid "silage" that can be stored for a prolonged period under a wide range of temperatures. This product has a sweet-sour smell and good nutritional value if it is converted for use as an ingredient in feed. While this process is not yet widely used in the U.S., related technologies have been applied in Europe, where a process has been developed for fermenting and pasteurizing the offal and sludges from slaughtering facilities. In North Carolina, on-farm fermentation will require careful management and daily maintenance.
Key idea: Anaerobic fermentation can stabilize carcasses for conversion and use in feeds, avoiding many of the environmental problems associated with burial, storage, and incineration.
Of all the technologies emerging for managing odor and wastes in swine production, perhaps the most mysterious is biogas generation. Logically, it should work. The natural microbial digestion of manure produces methane, a gas frequently used for firing boilers, generators, heaters, and other mechanical equipment. Simple systems for capturing methane under lagoon covers have been operated economically on dairy farms in North Carolina and elsewhere, reducing energy costs and odor. And scientists at North Carolina State University have demonstrated that a thermophilic digester can efficiently treat poultry manure and provide biogas for use on the farm. Several experts have reasonably assumed that swine producers might someday begin harvesting biogas as well.
Unfortunately, an economical system for producing biogas from swine manure has so far proved elusive. A number of problems have been reported, including the overprotection of ammonia, and methane generation has generally been unreliable, especially in simple systems using covered lagoons. Also, biogas production does not significantly reduce the volume of wastes to be handled.
Even so, a number of scientists feel that these problems can and will be solved, eventually making the technology an attractive option for swine producers. Because of relatively low prices for petroleum, demand for alternative energy sources has dwindled since the 1970s, making biogas less cost-effective and reducing the impetus to develop the technology.
In Denmark, the oil crisis of the 1970s led to a policy toward self-sufficiency in energy production, including the development of biogas plants for treating municipal sludges and animal manures. These plants were generally profitable until energy prices dropped, and they now operate with subsidies. For the most part, biogas plants in Denmark do not use thermophilic digestion with swine wastes because excess ammonia has in some cases shut the plant down. Following anaerobic treatment, the sludge, which has little odor, is returned to farmers for application on their fields, and there have been very few complaints from neighbors.
Because methane could, in theory, offset some of the costs of improved waste-treatment systems, the swine-odors issue has renewed interest in biogas production. At North Carolina State University, researchers have begun testing a system for thermophilic digestion using very advanced methods recently developed by poultry scientists. The project will treat swine manure at various concentrations, measuring odor and biogas production. Researchers will also evaluate the technology for its practical application.
Key idea: Despite the uneven performance of biogas systems tried in some swine operations, newer technologies may eventually offer producers an odor-management option that pays for itself in energy production.
A number of technologies for reducing odor have been developed for industries using or producing odorous compounds. These include
Because all of these systems incur significant costs in construction, operation, and maintenance, they generally have not been considered practical in swine production. As incentives for controlling odor increase, however, some of these technologies are being tested for use in agriculture.
Biological filters. Currently, the least costly technology for removing odors from large volumes of air is the biological filter. In biofiltration, odorous air passes through a filter containing microorganisms that break down volatile compounds into carbon dioxide, water, mineral salts, and other harmless products. The filtering medium may be peat, compost, soil, or some other low-cost, biologically active material. Biofiltration can remove 90 percent or more of volatile organic compounds, creates no secondary pollution, and is efficient in treating low concentrations of odorants (less than 20 ppm).
In Europe, biofiltration in agriculture has been limited primarily to large, centralized treatment plants. One rendering operation in the Netherlands began 15 years ago using five biological filters to reduce odor. These filters are air tunnels in the center of enormous concrete bunkers. Openings in the sides of the tunnels allow air to be forced through filters of hay and turf covered with tree bark. While these systems were very expensive to construct, each processes vast amounts of air, removing 95 percent of the odors released from the plant.
European scientists have tested various biofilters for odor control in swine operations, but most of these systems are expensive and have been susceptible to dust and clogging. Recently, however, a new, inexpensive biofiltration system has been developed in the Netherlands. In early tests, the system's bacterial monoculture has demonstrated an ability to scrub odor from large volumes of air.
A similar system is being tested at North Carolina State University, where researchers have begun evaluating a pilot-scale biofilter for use in treating the air exhausted from swine buildings. In the study, odorous air will pass through a filter of peat inoculated with one of several bacteria. Using gas chromatography and an odor-monitoring device, researchers will evaluate the biofilter's ability to reduce the levels of odorous compounds.
Key idea: With further testing and development, low-cost biological filters may become practical technologies for controlling swine odors.
Catalytic conversion. For the last several decades, regulatory pressures have promoted the development of compact, relatively low-cost devices for reducing air pollution. Today, catalytic converters are common in cars, woodstoves, and other products that burn fuel and therefore yield enough excess heat to covert the contaminants. Until recently, this technology was not considered practical for room-temperature installations on swine farms, where the energy costs would be high.
At North Carolina State University, researchers developing a catalytic converter for use on spacecraft have begun adapting the technology for swine operations. Unlike most catalytic converters, this version would use ultraviolet light instead of heat to neutralize contaminants.
As they adapt this technology for use on swine farms, researchers will attempt to incorporate low-cost components such as commercial fluorescent bulbs, and will test the rates at which various odorous compounds degrade. Because the compounds that cause swine odors occur in relatively low concentrations, it may be possible to treat them using a compact, economical converter.
Key idea: Researchers in North Carolina are developing a catalytic converter that would remove swine odors at room temperature using ultraviolet light.
A Palette of Options
This chapter has focused primarily on research and new technologies for waste management, odor measurement, and odor control. As the task force investigated each of these topics, we attempted to assemble a wide range of options with potential for application in North Carolina. In the process, we also sorted the options into two broad categories: those we could recommend for adoption today, and those that will need further study. In the next chapter, we will break these options out, one by one, along with some recommendations.
Before we do so, it is important to note that our focus in Chapter 4 has primarily been on the technologies themselves. We have not thoroughly explored the possible methods for developing or applying these technologies. By its nature, odor is an elusive and complex phenomenon, and any steps we take toward odor reduction will no doubt be complicated by a number of variables. In some cases, predictive models, both mathematical and physical, may help us account for this complexity and simulate the performance of various technologies before they reach the field.
But it is also necessary for us to recognize that no technical innovation occurs in a social or economic vacuum. As we consider new options for managing odor, it will be important to include research and analysis by economists, social scientists, and others who can assess the potential impact of each innovation on the lives and livelihoods of North Carolinians.
Practical Optionsfor reducing swine odors
We can now recommend a number of practical options for reducing swine odors. In this chapter, we present options currently available for new and existing operations, as well as those options which may be available with further research and new technologies. Finally, we consider several approaches to policy.
for new and existing operations
Most of the recommendations that follow are practical for virtually every commercial-scale swine operation in North Carolina. Indeed, producers already have adopted some of these measures, or will do so under waste-management plans now required in North Carolina. New facilities can be designed, sited, and managed in accordance with principles outlined in this section. Older production facilities can be kept clean and can be retrofitted with some of the improvements listed in this chapter. However, it is safe to assume that most of these changes will occur at some cost--in money, time, or convenience.
Adequate controls and attention to detail in the management of swine operations will reduce odors by preventing the buildup and decay of urine, manure, and dust and by ensuring the efficient operation of waste-handling systems.
Each component of the system for removing, collecting, storing, and treating manures and urine is a source of odor. The primary cause of these odors is the release of gases during the agitation and mixing of liquids and sludges. Remedies include:
Some lagoons are undersized or poorly designed. Providing adequate lagoons reduces odor and helps protect water quality. Available options are:
Frequently, the contents of lagoons are applied to pastures or cropland. Odors may be released during pumping, transport, and application. Available options, in approximate order of increasing cost, include:
Disposal of Dead Pigs
Dead pigs should be collected and disposed of promptly, preferably by a commercial rendering service. If carcasses are disposed of on-site, one of the following methods should be used:
Site selection and conditions
with new knowledge and technologies
While the steps outlined above would help reduce odors at many locations new technologies are also needed. Each of the new technologies described in Chapter 4 holds promise. We recommend an accelerated, comprehensive program of research and development to ensure that these options become available for practical use as soon as possible.
Some of this work has already begun at through North Carolina State University. The table on page 76 lists current and recent research projects. NCSU's new Animal and Poultry Waste Management Center, a cooperative endeavor of business, government, and the university, will include state-of-the art technologies for treating and recycling wastes, for converting them into value-added products, and for reducing odors. Representation on the Swine Odors Task Force has enabled the center to gain a head start on many of the priority needs described below.
Odor measurement and characterization
Several technologies for measuring certain constituents of odor show promise. However, more research and development is needed to quantify the components of odor and to correlate these with the subjective responses of human "odor panels." Careful measurements and correlations will serve as the bases for thresholds and guidelines in odor control.
Additives and odor reducers
While additives, deodorants, and masking agents are gaining popularity, research is needed to evaluate the effectiveness, safety, and appropriate use of the many feed additives and odor-control products available to producers.
Improved ventilation and odor removal
Several emerging technologies show promise for reducing dust or for treating the air exhausted from swine houses.
Improved houses and waste-handling systems
Many of the swine facilities in current use were designed before cleanliness and waste treatment efficiency became critical issues. Recent public pressure to reduce odor and protect water quality creates incentives for engineered structures that improve performance and allow for easy maintenance and cleaning. Some of the technologies developed in Europe may prove useful in North Carolina, once they have been adapted for local conditions.
Energy recovery and value-added products
A wide range of options show promise for recovery of nutrients and energy in waste-management systems, and for converting wastes into useful products. These include:
Composting also holds promise for the disposal of dead pigs. Composting of swine carcasses is not now permitted in North Carolina, but recent research at NCSU indicates that a well-managed composting system might help reduce odor emissions and protect water quality. Like anaerobic fermentation, composting offers the opportunity to recover nutrients and use them in various products.
While the principles of composting are well established, further research and development are needed to establish practical, economical composting methods for swine operations.
Simulation and modeling
Advanced methods for predicting the performance of complex systems show promise in several areas. For example:
Some model already have been applied to predict the distribution of carbon dioxide, dust, and odor distribution in livestock buildings. Rapid improvements in computer technology and the volume of data being obtained from real buildings will increase the usefulness of numerical modeling and simulations.
Policy options for reducing swine odors range from programs encouraging voluntary compliance to statewide regulation. Many of the measures recommended above can be adopted at relatively low cost, and some may even yield gains in production efficiency and profitability. For improvements of this type, a statewide program combining public information, education, and voluntary compliance could yield significant benefits. In such a program, the North Carolina Cooperative Extension Service could work closely with state and federal agencies, especially those related to air quality or soil and water resources. Typically, animal production systems that conserve soils and protect water quality also tend to reduce odor. A comprehensive, inter-agency approach could help ensure the design and adoption of appropriate new technologies.
A good example of voluntary action is in Harnett County, where a committee representing diverse groups of citizens established guidelines for new swine facilities and launched a campaign for improving waste-management practices. The program has attained a high level of voluntary compliance among swine operations.
It is unlikely, however, that North Carolina will solve its swine-odor problems without cost or inconvenience. For measures that require significant investment or changes in management practices, a program of incentives similar to those in the Agricultural Cost-Share Program would increase voluntary adoption. Such a program would also increase the effectiveness of educational efforts conducted by Extension and others.
If an incentives-based approach is chosen, there are several options worth investigating:
1. Certification. The "Green Label" program used in Europe has successfully reduced ammonia emissions by certifying producers who meet a set of measurable criteria. Benefits in certification programs typically include relief from regulatory intervention for an extended period of time, tax breaks, investment credits, or other financial incentives. Certification might also offer a marketing advantage if products were packaged with a label attesting to the producer's environmentally appropriate methods of production.
2. Cost sharing. Using a program of grants or other financial assistance, government and industry could share the cost of upgrading facilities to reduce odor.
3. Site-by-site problem solving. Because odor problems tend to be site-specific, no single set of odor-reduction measures will apply to every facility. With adequate support, interdisciplinary teams of scientists could visit locations where swine odors are a problem. These teams could make site-specific recommendations for reducing odor and resolving conflict.
There are many different options for regulatory measures that might address the swine-odors problem. Some of these measures might also apply to water quality and other environmental concerns. For example, the state's new ".0200" regulations, which require producers to file waste-management plans, will probably help reduce odor at many sites. In general, several other approaches might be considered:
1. Chemical-specific regulations. This type of regulation would set targets or limits for one or more specific chemicals that could be quantitatively measured and monitored. In Europe, ammonia is the chemical on which standards are based, primarily because of an emphasis on acid rain and water quality, not odor.
2. Perceived-odor thresholds. Regulations based on the human perception of odor could include thresholds established by odor panels using olfactometers or other such instruments.
3. "Bad-actor" laws. Some environmental regulations are complaint-driven. Typically, a potential violator is identified by complaints. When the regulatory agency has confirmed that the "bad actor" is in violation of standards, a process is prescribed for correcting the problems. In the case of swine odors, a team of specialists could be called upon to help violators resolve odor problems and achieve compliance.
State and local governments vary widely in their approach to regulation, and few have attempted to write regulations specific to odor. In North Carolina, new operations with 250 or more swine must develop and submit a waste-management plan based on specifications provided by the Natural Resources Conservation Service (NRCS) and adopted by the North Carolina Soil and Water Conservation Commission. The commission designates technical specialists who may certify the plans. These regulations took effect in January, 1993 with a phase-in for existing systems. Existing operations with 250 or more swine must have registered by December 31, 1993, and must be certified by December 31, 1997.
In neighboring states, most regulations have focused on nutrients and water quality, and many are based upon standards set by the NRCS. The following examples are intended as illustrations only, not as recommendations for policy:
Whatever the policies North Carolina chooses, success will depend in part on the involvement of citizens as well as producers in the selection and formulation of each incentive program or regulatory measure. We recommend public participation early and often in the decision-making process.
Standards and Criteria
Whether voluntary or regulated, measures to reduce odors should be based upon clear, objective standards. These standards might be prescriptive, performative, or a combination of the two. Prescriptive standards might require some of the specific improvements to equipment, facilities, and procedures described in this section. Performative standards might require that operators prevent odors from exceeding certain thresholds.
Performative standards based on odor thresholds must be carefully researched, tested, and designed, because measuring odor is complex. Odors vary, people react to them differently, and no device for measuring odors can exactly simulate a human's olfactory sense. The methods and technologies for odor measurement and analysis can and should be improved. We need further research into the physical and chemical properties of odor, as well as human response to odors.
In the meanwhile, several devices now available provide accurate, reliable measurements of several airborne compounds commonly associated with nuisance odors. Therefore the technology does exist to establish reasonable, objective thresholds for some odorous compounds.
For each of the currently available management options described in this chapter, performance criteria should be developed and data collected so that management improvements can be recommended. An interdisciplinary team should establish these criteria in cooperation with industry, local communities, and the appropriate state agencies.
The Need for New Directions
In the final two chapters of our report, we have covered several emerging technologies with promise for reducing odor. We have also covered quite a few specific measures for improving swine-production systems as they are designed today. But we have not yet talked about some of the more fundamental changes that might be necessary to ensure a productive future for the swine industry in North Carolina.
In our view, the university and industry should strengthen their partnership and commit themselves to a long-range plan for improving the design and operation of swine facilities in North Carolina. In broad strokes, that plan would probably include steps for moving in several new directions:
1. Separate the urine from manure. Experience in Europe has clearly demonstrated the benefits of separating urine from manure. Not only does this step reduce the volume of water to be disposed of and help simplify treatment and odor reduction, it also provides better raw materials for value-added products.
2. Continue to improve waste-treatment systems. While lagoons offer several advantages for storing and treating wastes, they also present a few potential problems. Lagoons can release significant amounts of ammonia into the atmosphere. As the number of lagoons increases in North Carolina, atmospheric ammonia may tend to acidify rainfall in some locations. In addition, there is evidence that some lagoons leak. NCSU is investigating the extent to which seepage from lagoons might be affecting groundwater resources. We need more information about the ability of various kinds of lagoons to remain sealed and protect water quality. We also need new technologies for improving the performance of lagoons. For some locations, it may be necessary to consider the use of alternative storage and treatment systems, especially those which separate liquids from solids.
3. Phase in the incorporation of sludges and slurries. The prompt incorporation of land-applied sludges and slurries could reduce odor and involve more of the soil in treatment.
4. Continue to improve building design. Not all swine buildings include features now recommended by NCSU. Industry and the university should collaborate to apply research-based information and advanced modeling techniques to improve the design of waste-management systems, floors, walls, and feeding and ventilation systems.
The Multiple Benefits of Better Management
This report has focused primarily on the problem of swine odors and how to reduce them. But as North Carolina weighs the costs and benefits of such an effort, we should recognize that most of the improvements recommended here will yield benefits in addition to odor reduction. For instance, most practices that reduce odors inside swine houses also reduce the risk of illness among workers and pigs. More efficient feeding improves the productivity of animals. And practices that improve the handling, storage, and treatment of manures also tend to reduce the risk of contamination to streams and groundwater supplies.
Clearly, the problem of swine odors cannot be viewed in isolation. Nor should the issues be reduced to a them-or-us conflict between swine producers and their neighbors. Our hope is that the findings of this report will help improve communication among all of the parties involved. In many locations, the best remedy for swine odors will be a clean, efficient, profitable operation. And that is exactly the sort of operation most producers strive to achieve.
With its strong universities and agencies, North Carolina is well positioned to provide the public information, education, research, technical development, and appropriate public policies necessary to resolve conflicts and promote a cleaner, more comfortable environment for swine producers and their neighbors.
Swine Odor Task Force
March 1, 1995
Dr. Johnny C. Wynne, Director,
North Carolina Agricultural Research Service,
North Carolina State University
Dr. Roger G. Crickenberger, Associate State Leader,
Agriculture and Natural Resources,
North Carolina Cooperative Extension Service
Dr. David B. Beasley, Head, Biological and Agricultural Engineering,
North Carolina State University
Task Force Members
Mr. Allain C. Andry, Agricultural and Resource Economics
Dr. James C. Barker, Biological and Agricultural Engineering
Dr. Robert W. Bottcher, Biological and Agricultural Engineering
Dr. Jon A. Brandt, Head, Agricultural and Resource Economics
Dr. Darwin C. Braund, Associate Department Head, Animal Science
Dr. Thomas A. Carter, Poultry Science
Dr. William B. Clifford, Head, Sociology and Anthropology
Dr. Peter R. Ferket, Poultry Science
Dr. Jeffrey A. Hansen, Animal Science
Dr. Raymond W. Harvey, Animal Science
Dr. Thomas J. Hoban, Sociology and Anthropology
Dr. Evan E. Jones, Animal Science and Biochemistry
Dr. Rick Langley, Occupational and Environmental Medicine, Duke University
Dr. Benjamin T. McDaniel, Animal Science
Dr. William E. "Morgan" Morrow, Animal Science
Dr. Jerome J. Perry, Microbiology
Dr. Matthew Poore, Animal Science
Dr. L. M. Safley Jr., Biological and Agricultural Engineering
Dr. Susan S. Schiffman, Medical Psychology, Duke University
Dr. Charles M. Stanislaw, Animal Science
Dr. Tomislav Vukina, Agricultural and Resource Economics
Dr. Philip W. Westerman, Biological and Agricultural Engineering
Dr. John C. Wilk, Animal Science
Dr. C. M. (Mike) Williams, Animal and Poultry Waste-Management Center
Dr. Kelly D. Zering, Agricultural and Resource Economics
Dr. David H. Moreau, Water Resources Research Institute
Mr. Bill Holman, Sierra Club
Mr. Tom Ellis, North Carolina Department of Agriculture
Mr. William B. Jenkins, North Carolina Farm Bureau Federation
Mr. Robert H. Caldwell, North Carolina State Grange
Mr. and Mrs. Craig King, Producers
Mr. David Harding, North Carolina Department of Environment, Health, and Natural Resources
Mr. Jeff Turner, Mayor of Pink Hill, North Carolina
Initiation Completion Title Investigators Date Date Funding
Swine Productivity Improvement of Swine See, M. T. 10/1/94 9/30/97 Hatch through Quantitative Genetic Evaluation Nutrition and Management Coffey, M. T. 10/1/88 9/30/98 Hatch Swine Genetic Regulation of Robison, O. W. 12/1/90 9/30/95 Hatch Pork Production Performance Testing of Jones, J. R. 10/1/90 9/30/95 State Boars Neural Regulation of Flowers, W. L. 10/1/89 9/30/94 State Follicular Growth in Swine The Actions of Calcium on Alston Mills, B. 10/1/91 9/30/96 Hatch Mammary Gland Development and Differentiation Waste Management Research Administration Transformation and Loss of Harvey, R. W. 1/1/93 9/30/95 State Nitrogen in Grazed and Ungrazed Fields Biological and Agricultural Humenik, F. J. 1/1/93 9/30/95 State Engineering Genetic Studies of a Bac- Shih, J. C. 1/1/93 9/30/95 State terial Keratinase for the Bio-Conversion of Proteinaceous Wastes to Nutrient Resources Livestock Waste Management Hoban, T. J. 1/1/93 9/30/95 State in North Carolina: Barriers and Opportunities Safe and Efficient use of Mikkelsen, R.L. 1/1/93 9/30/95 State Nutrients from Land-applied wastes Swine Odors Task Force Swine Odor Task Force Wynne, J. C. 10/1/93 9/30/95 State Understanding Odor Molecular Aspects of Anholt, R. R. 1/1/94 9/30/95 State Olfaction Cleaner Air and Odor Control Biofilters for Removing Westerman, P. W., 9/1/94 mid-1996 State Odorous Compounds in Exhaust et al. Air from Swine Buildings Utilizing Byproducts to Bottcher, R. W. 9/1/94 mid-1996 State Clean Air in Swine Buildings Jones, J. R. Development of a Consensus Williams, C. M., 9/1/94 mid-1996 State Swine Odor Control Product et al. Evaluation Protocol Economics of Swine Production Effects of Production and Holt, M. T. 8/1/94 9/30/95 State Price Risk on Markets for Southern Agricultural Commodities Financial Performance and Perrin, R. K. 10/1/89 9/30/94 Hatch Productivity of North Carolina Agriculture Improved Systems and Facilities Environmental Control Systems Bottcher, R. W. 10/1/94 9/30/95 State for Poultry and Livestock Waste Management and Water Quality Selection of Plants for Stucky, J. M. 1/1/94 9/30/98 State Constructed Wetlands for Wastewater Treatment Management of Animal Waste Safley, L. M., 10/1/90 9/30/95 Hatch in Support of Sustainable Westerman, P. W. Agriculture and Water Quality Genesis and Hydrologic Kleiss, H. J. 10/1/90 9/30/94 Hatch Characteristics of Soils on the Piedmont Coastal Plain Fall Line [subsurface movement of waste] Groundwater Contamination Huffman, R. L. 10/1/90 9/30/95 Hatch Potentials of Agricultural Practices Environmentally Compatible Bilderback, T.E. 10/1/91 9/30/96 Hatch Nursery Crop Production Practices [wastewater runoff and water quality] Functional Development of Broome, S. W., 10/1/91 9/30/96 Hatch Constructed Wetlands and Seneca, E. D. Coastal Dunes Watershed Management Jennings, G. D. 10/1/94 9/30/99 Hatch Strategies to Protect Water Quality Interactive Effects of Water Skaggs, R. W., 9/15/94 9/30/96 Grant Table Management and Ferti- Lilly, J. P. lization on Water Quality Cumulative Impacts of Land Skaggs, R. W., 9/1/94 8/31/97 Grant Use and BMPs on Water Quality Lilly, J. P. in Coastal Watersheds Molecular Phylogenetic Survey Brown, T. T. 9/1/94 mid-1996 State of Mehanogens in Waste- Treatment Systems Predicting Nutrient Release Mikkelsen, R.L., 9/1/94 mid-1996 State from Food and Animal Waste Wollum, A. G. Products Land-Applied Waste for Forage and Crops Pratical Forage Systems for Mueller, J. P., 10/1/91 9/30/95 State Ruminant Livestock in North Green, J. P. Carolina [using swine lagoon liquid] Nitrogen Waste Byproducts in Harvey, R. W. 10/1/91 9/30/96 Hatch Beef Cattle Feeding Improving Nutrient Efficiency Mikkelsen, R. L. 10/1/92 9/30/97 Hatch for Crop Production in North Carolina Developing an Enzymatic Assay Mikkelsen, R. L. 9/15/92 9/30/93 CSRS for Predicting Nitrogen Release from Organic Residues Pest Management Poultry and Livestock Inte- Axtell, R. C. 10/1/93 9/30/98 Hatch grated Pest Management Management Systems for Axtell, R. C. 10/1/88 9/30/93 Hatch Arthropods Affecting Poultry, Livestock, and Humans Development of Entomo- Brooks, W. M. 10/1/90 9/30/95 Hatch pathogens as Microbial Control Agents Against Insect Pests Products from Animal Waste Conversion of Agricultural Williams, C. M., 9/1/94 8/31/96 Grant Waste to Value-Added Wynne, J. C. Utilizable Products A System for the Development Jones, J. R., 9/1/94 mid-1996 State of Value-Added Products from et al. Swine Manure and Peanut Shells Recovery of Solids from Westerman, P.W., 9/1/94 mid-1996 State Flushed Swine Manure for et al. Utilization Genetically Engineered Micro- Jones, J. R. 9/1/94 mid-1996 State organisms for Utilization of Ammonia and other Nitrogenous Compounds from Animal Manure Optimizing the use of Live- Williams, C. M., 9/1/94 mid-1996 State stock and Poultry Manures as et al. a Co-Substrate and Source of Inorganic Nutrients for the Biodegradation of Hazardous Compounds Composting: Turning Swine Morrow, W. E., 9/1/94 mid-1996 State Carcasses into Humus et al. Optimizing the Proteolytic Miller, E. S., 9/1/94 mid-1996 State Degradation of Animal By- Shih, J. C. H. Products Safety and Health Safety and Health of Suggs, C. W., 10/1/87 9/30/93 Hatch Agricultural Workers Abrams, C. F., Stikeleater, L. F.