W.E. Morgan Morrow
Department of Animal Science
North Carolina State University
Raleigh, NC 27695

As the swine industry in North Carolina undergoes rapid expansion not only is the density of swine in the state increasing but also the amount of waste produced. For 1993:

Not only does disposal of this waste present a problem but increasingly the public is concerned about the odor that can result from storing and disposing of the waste.

Understanding and dealing with the public's concerns about odor while maintaining growth of the hog industry has presented many challenges. To minimize offensive odors, our industry has not had the information necessary to determine the best sites for a hog unit, or decide on the best waste handling and manure disposal system. It is unrealistic, and probably unnecessary, to expect the swine industry to completely eliminate odors from its sites. The challenge is to develop the science, techniques, management, and public education necessary so that all parties can coexist. The problem and its solution are complex because so many factors are involved.

Odor Chemistry

In this high-technology era it is a paradox that we still do not have an accurate method for measuring odors. The need is obvious. If you can't measure it then how can you do anything about it. The answer lies in understanding the difference between the chemicals you smell and how you perceive and react to those chemicals. Very often people think that swine odor is caused by ammonia and hydrogen sulfide and all the scientists have to do is measure the concentration of those chemicals. Unfortunately, odor is a very complex mixture of gases, chemicals, dust, biological debris, and living organisms. In fact, about 600 chemicals are known to be involved in swine odor. It is technically relatively easy to measure the concentration of chemicals in an odor, the difficulty comes in how people perceive that odor.

People Chemistry

When different people smell an odor not only may they not believe it smells the same but they also may have very different reactions to the odor. The human nose is a very sensitive sensory system and every nose is unique. The olfactory systems can be biased by thought processes or by long-term or highly concentrated odors. For example, if you live by a hog farm, chances are that you will gradually become desensitized and eventually not smell the hogs at all unless the odor is very strong. Consequently, the correlation between human noses and analytical monitoring systems is poor.

Current Analytical Techniques

Ammonia and hydrogen sulfide are measured and used as indicators for the other chemicals in swine odor.

Scentometer. This hand-held instrument dilutes the air with odor-free air. It is not satisfactory in a area with a lot of odor but is used at the property line.

Olfactometer. This is similar to a scentometer in that the machine mixes in fresh air. The collected samples are then submitted to an odor panel, 4-8 people, and threshold limits are established.

Cotton fabric swatches. Cotton swatches are hung in the odor stream, collected, then submitted to an odor panel.

Sources of Odor

Odors result from the anaerobic decomposition of swine waste which are then carried by airborne dust, other particles, and as a gas to the environment.

Different researchers have attributed either the barns or the lagoon as the primary source of odor on hog farms. In reality, it probably varies by farm and depends more on how each location is built and managed. A properly managed pit-recharge barn is less likely to be a problem than a poorly managed barn with a deep pit. Similarly, a well designed and operated lagoon will have few complaints compared to one that is improperly sized, has poorly placed the input lines, and the manager sprays the effluent on windy days when the neighbors are at home.

Odors dispersed when managers spread or spray manure on pastures generates the most complaints from the public. Injecting slurry into the soil is the most effective method for reducing odors.

The Law

Although North Carolina has a Right-to-Farm law it does not, no should it, protect farmers when their activities prevent their neighbors from enjoying "reasonable" use of their land. What is "reasonable" is decided by the courts when a nuisance lawsuit is bought against the farmer. The courts decide whether a use is "reasonable by examining the nature of activities in the surrounding area and weighing the relative social value of the competing uses, the degree of harm, and the burden on each side to minimize the harm. A completely lawful use of a property can be a nuisance if it is not located in an appropriate area or if the operation in not properly conducted or maintained.

Opportunities for Controlling Odors

Categories for controlling odor include:

Dietary Additives

This collection of chemicals that include charcoal, calcium bentonite, and zeolite work by adsorbing noxious chemicals such as ammonia. Including them in a ration is limited by their bulk and cost. A recent alternative is sarsaponin, a plant steroid, extracted from the plant Yucca shidegera. Researchers have demonstrated a 5% increase in average daily gain and 2% increase in feed/gain for finishing hogs fed sarsaponin. In addition, sarsaponin can also reduce the level of ammonia in hog confinement buildings. Adding 120g/ton De-Odorase, a combination of sarsaponin and a bacterial enzyme, to pig feed has been demonstrated to reduce atmospheric ammonia from 40 to 12.5 ppm after 4 weeks and to 6.25ppm after 6 weeks. Sarsaponin probably works by either inhibiting the enzyme urease that produces ammonia or by stimulating the growth of positive microorganisms. As an bonus, sarsaponin is not absorbed by the pig and continues its work in the lagoon.

Adding Chemicals to the Waste

For years researchers and salesmen have searched for the perfect additive that will prevent odors in stored waste.

In general, masking agents and reactants are most effective but are very short lived and may only be useful for short term storage of waste.

Research Opportunities

Research is continuing at NCSU on some novel methods for reducing odors. Dr. David Ollis in Chemical engineering is testing an ultra-violet light activated, low-temperature catalyst that can oxidize odorous chemicals in the exhaust air stream from swine buildings. The system will probably work but it may be too expensive to implement.

A technology that may be economically adapted to many swine buildings is the use of biological filters to microbially oxidize odorous compounds. Research is underway at NCSU by Dr. Phil Westerman and others in the Department of Biological and Agricultural Engineering to evaluate a pilot-scale peat biofilter to treat exhaust air from a swine building (finishing floor with pits) at typical ventilation rates for North Carolina swine houses. Initial treatments are various inoculants for the biofilter:

Each treatment will have two replications each. After the initial inoculant evaluation, the best inoculant treatment will be used for evaluating two or three different residue times (air flow rates). Removal of odorous compounds would be evaluated by:

Direction for Future Research

Utilize physical and mathematical modeling to determine optimal design of buildings and spacing to disperse and reduce odor problems

Develop new ventilation strategies and technologies to reduce dust production and movement inside and outside production buildings

Develop "friendly" strategies for siting and building production facilities based on consensus and with attention to both odor and water quality concerns

Continue developing technologies to neutralize odors that do develop

Take-Home Message

The odor issue is a very complex one. Much is already known about odor but we need to know a lot more to enable us to better manage the situation. Farm managers already can do a lot to minimize the bad effects of swine odor. These range from the very simple and cheap management decision to not operate spray guns unless conditions optimal to the very complex and expensive option of installing an anaerobic methane gas generator. Research continues across the USA to minimize the effect of swine odors.