The following odor discussion is assembled from several non copyrighted
publications available on the World Wide Web. Two postings in particular were
used because of the way the authors assembled their material. These postings
were from Dr. Yuanhui Zhang, University of Illinois, and Dr. Jay Harmon, Iowa
State University.
Contact: Environmental Engineer, National Water Management Center (501)
210-8900.
A person’s perceptions are based on experiences that they have had throughout
their life. For some, this experience includes agricultural production that
makes them realize that some odors naturally occur with livestock production,
and therefore some level of odor is acceptable to them. Other people may not
have been exposed to such situations and may perceive any livestock odors as
being much more offensive. To these people livestock odor is a nuisance. In many
cases odors can not be eliminated, only minimized through proper management and
good neighbor relations.
Livestock production generates numerous odors. Those odors vary greatly, and
the offensiveness of each odor is dependent upon the person smelling the odor.
Some odors are generated by the animals and the dander from their bodies; some
odors are from the animals’ feed; and some odors, usually the strongest, are
from the livestock manure and decomposition of that manure. So when do odors go
from being acceptable to unacceptable? Much of that determination depends on
when the odor is considered to be a nuisance. How frequent an odor occurs and
the intensity of the odor often are factors considered in whether or not an odor
is a nuisance. Since the tolerance of these factors differs for individual
people, there is no clear cut answer for what does constitute a nuisance. Many
times other things affect how people respond to detected odors, such as the size
or ownership of a livestock unit. Some people are not happy with the
construction of larger livestock units in their neighborhood, so they have an
immediate bias on how much of an odor problem is generated by such an operation.
Larger operations do have the potential for more odor because of more animals,
however it may actually be the dislike of the production unit that causes more
of a problem than the actual odor produced by the unit.
The odors released from livestock production may affect numerous people, and
more importantly may impact each person differently. In addition to the
livestock producers and their families, others exposed to odors include
neighbors, people that pass by on roadways and anyone who uses nearby public
areas. The number of people affected by any one livestock operation can vary
greatly due to the proximity of housing developments or location along major
roadways or recreational areas. The more people affected, the greater the chance
that some will find the odors offensive. People all have personal differences on
how sensitive they are to odors and on what is considered acceptable. These
differences in acceptability are very subjective, and are often based on
attitudes or previous experiences. A person’s memory of an unpleasant prior
experience often influences their attitude toward an enterprise. Objections also
arise from people feeling they have no power over their own situation and are
forced to be exposed to odors.
Dr. Ron Miner of Oregon State University has spoken and written extensively
about the psychology of odors, and a brief quote from a paper of his is included
here.
"The psychological response to odors is more complex and less well understood
than the physiology which has been extensively explored during the past thirty
years. Evidence suggests that each of us learns to like or dislike certain
odors. Children like almost all smells. It is only as we mature and begin to
talk about the odors that we develop a sense of likes and dislikes. Food tastes
are very much related to the odors from those foods. Subtle spicing would be
ineffective except for the multitude of differences we can detect.
Only recently have scientists begun to relate these complex psychological
reactions to the ways in which people respond to specific odor sources such as
those associated with pork production. Clearly, individuals react differently to
the smell of any particular odor source. There are experiences of people who
react to swine lagoon odors with an emotional intensity that others would find
entirely unreasonable. Recent observations suggest these are honest and accurate
reactions. Whether these responses are so intense because they have an objection
to the odor source based on other factors is unclear at this point. It has been
observed, however, that there are fewer objections within a community to those
odors that are a traditional part of the community, or are produced by an
agricultural operation of an appreciated and esteemed member of the community,
than to an odor generated by an outside agent’s operation that may alter the
traditional social structure. Thus, a large high tech swine confinement system
relocating to an area of traditional style pork production can expect to have
the local residents find the odor more objectionable than an odor of similar
intensity from a more conventional system of pork production." (Miner, 1995)
There continues to be numerous research efforts to develop a tool to "model"
the production of odor and it’s detectibility away from the odor producing site.
Some of the tools are in wide use across the country. Baumgartner Environics,
Inc., for example, employs proprietary modeling software to estimate the
emission of odorous gasses from the surface of an outdoor manure storage
facility, to predict odorous gas transport off site and, finally, to map the
concentration of a gas at a given distance downwind against the odor threshold
of a human population for that gas. This information is then used to evaluate
which method of odor control will best provide needed odor control. (Baumgartner,
2000).
Causes of odor and remedial measures
There are three primary sources of odor: livestock facilities and the animals
contained within, manure storage structures, and application of livestock manure
to agricultural land. The odor itself is a combination of many different
compounds and gases. Many of the compounds that combine to produce odors are
the result of anaerobic bacterial decomposition of manure during storage.
Decomposition rate is affected by temperature, pH and moisture. Warm, moist
conditions favor bacterial action, and therefore increase decomposition and odor
generation. Some odorous compounds produced are: sulfides, organic acids,
carbonyls, indoles, skatoles, and phenols. A number of factors, including which
compounds are present and in what combinations, affect the odor emitted and the
intensity of that odor.
Odor from buildings and lots
There are primarily three gases produced by manure decomposition that are
major components. Those gases are hydrogen sulfide, amines and methyl mercaptans.
All of these are present in the atmosphere in dilute concentrations but may be
present in higher concentrations near livestock buildings. Hydrogen sulfide
(H2S) has a rotten egg smell at low concentrations. At greater concentrations,
which may occur in a deep pit building during manure agitation, the gas cannot
be smelled due to paralysis of the olfactory senses, and can actually cause
death due to respiratory arrest. H2S is heavier than air so it accumulates in
pits and other low lying, unventilated areas. Hydrogen sulfide concentrations
should not be high enough to cause concern as you move away from the manure
storage structure.
Dust is also a component of odor and may be the most detrimental because it
can be transported long distances along air currents. Dust particles act as a
transport mechanism for odor. Gases and compounds disperse but dust will carry
compounds farther. Dust particles may also deposit next to olfactory cells where
the odor can continue to affect a person. The dust can come from many sources,
including dried manure, feed and animal hair or skin.
Siting livestock buildings
A good philosophy when siting livestock buildings is to always prevent odor
problems rather than cover them up. Selecting appropriate building sites can
go a long way toward minimizing odor problems. Some people may consider this to
only be important when purchasing land or building a farmstead from scratch. But
in reality, it is important to evaluate a building site before investing much in
improvements or expansion. Such an investment in a site that may have potential
odor problems probably would not be wise.
Topography
Topography around a building site is very important since it affects air
movement. Relatively flat sites that have good air movement and mixing are
good places to build livestock facilities. It is best to avoid hilltops
above residences in a valley, as odors may travel down hills. On calm nights
cool air drains from higher to lower elevations. Any odors from livestock
facilities will travel with the cooler air, thus creating potential odor
problems. If there are no residences at lower elevations, hilltops are a good
location for livestock buildings, especially naturally ventilated ones.
Wind
Wind direction has a major impact on how odors travel. Check the direction of
prevailing winds and compare them with the direction toward neighboring
residences, public use areas, highways, population centers and also any areas to
be developed in the future. If the summer prevailing wind is toward any such
places, it would probably be best to choose another site. In Iowa, for
example, winds typically come from the northwest in winter and south to
southwest in summer. Therefore, preferred locations for facilities are straight
north or straight east of housing to minimize potential problems.
Distance
In addition to wind direction, distance is important. Odor intensity
decreases as distance from the source increases. Distance allows fresh air to
mix with the odors, resulting in decreased odor intensity. Separation distances
are based on the odor source type and the size of the operation. Required
distances typically range from 750 to 2,500 feet. There are numerous
mathematical models available in the international community for predicting odor
intensity at various distances which complement efforts such as
Baumgartner mentioned
above.
Building orientation
Building orientation also has an impact on the odor emitted. Buildings or
outdoor manure storages that are exposed broad side to neighbors are more likely
to cause odor problems a greater percentage of the time due to the fact that
there is a much larger building surface area exposed toward the direction of the
neighbors. Therefore, it is advisable to orient buildings with the narrow
side toward neighbors. An exception to this is naturally ventilated
buildings, in which the wind direction needed for proper ventilation is of more
concern than exposure to neighbors. However, if neighbors or a public use area
is not far away, it may be best to consider relocation of a naturally ventilated
building. If potential odor problems are a concern, it may be better to
construct a mechanically ventilated building and orient it to reduce exposure or
find a different site.
Appearance
The importance a person’s perception has on their judgment has already been
discussed. This is also true with regard to the appearance of livestock
facilities. Well-maintained production units usually are not perceived to
smell as bad as units that look run-down. Nice landscaping and a regularly
mowed lawn will also encourage workers to do a better job of cleaning up spilled
feed and disposing of livestock carcasses. A production site that is overgrown
with weeds and has junk accumulated throughout the site certainly wouldn’t
encourage workers to keep everything tidy. Properly planted and maintained
windbreaks can serve a number of functions. Windbreaks that shield the
production site from the view of passers-by may decrease the chance of odor
complaints. When people cannot see the source of an odor, they are less likely
to notice an odor or complain about it. Windbreaks also cause air to be lifted
up, which causes more mixing of fresh air with the odorous air, thus diluting
the odor effect. However, wind breaks need to be used with caution around
naturally ventilated buildings because they can reduce the air flow through
buildings and create ventilation problems. More about vegetated barriers or
shelterbelts below.
Impacts of dust
Much of the problem odors generated by livestock buildings and lots can be
attributed to dust production and release. Excessive dust particles are an air
pollution problem and can transport odors some distance. Animal odors adhere to
dust particles and can easily be carried long distances on dust, from which the
odors are then released over time. Reducing dust in an animal confinement
building can substantially cut odor levels downwind. Dust from animal facilities
is very different from other types of dust such as field dust. The dust:
- is biologically active – it contains a variety of organic compounds,
bacteria, fungi, endotoxins and dust mites, making the dust potentially
detrimental to the health and comfort of animals and workers.
- is highly concentrated – it is typically ten or even one hundred times
more concentrated than in buildings such as an office. This feature makes
conventional air cleaning technologies such as filtration uneconomical because
they require frequent cleaning or replacement of a filter element. spans a
wide spectrum of particle sizes and shapes – dust particles from a swine
building, for example, are composed of dander, hair, feed dust and fecal
materials, and range in size from less than one micron (one millionth of a
meter) to a hundred microns in diameter. (Particles smaller than about 30
microns are generally not visible to the unaided eye.)
Defining the characteristics of animal building dust is very important to the
applied odor-control research. Quantifying the odor carried on different sizes
of dust particles will allow technologists to optimize their strategies for
removing the dust and odor. The size of a dust particle affects its behavior in
the air and in the human respiratory system. The respirable particles (smaller
than 10 microns in diameter, similar to tobacco smoke) are responsible for the
health and odor problems because, for one thing, particles that size can travel
deep into the lungs. Large particles (larger than 10 microns) usually bypass the
nose or are trapped in the respiratory tract and are naturally kept out of the
lungs. Particles of all sizes may contribute to odor transport from the animal
building.
There are a number of methods to reduce the dust generated and released into
the air. One control option is to clean the building frequently and remove dust
that has accumulated on gates, feeders and walls. This decreases the amount of
dust that can be stirred up and released into the air. Dust released from feed
can be reduced by using feed drops that extend down into the feeders and lids to
close the feeders. Adding a small amount of fat to the feed or pelleting the
feed are other methods of reducing feed dust. Air stirring fans can dramatically
increase airborne dust concentrations.
Proper humidity levels (50 to 70 percent) will reduce dust build up and
proper ventilation will help livestock develop good dunging patterns, which in
conjunction with good flooring, allows manure to drop through the flooring
quickly. Diluted manure is less likely to volatilize gases. Outside livestock
lots should be well-drained and kept as dry as possible. If water is not given a
chance to accumulate, less bacterial decomposition will occur; and therefore,
less odor is produced. Accumulated manure should be scraped and hauled as
frequently as possible.
Biofilters
Filters can be used to reduce the dust particles in the air. Biological
filters, or "biofilters" are used to cleanse the air of odor and dust. These
filters consist of biological matter, such as peat moss or wet wood blocks
which, when kept moist, fosters bacterial growth. The odorous air is passed
through this filter where microorganisms break down the odorous compounds to
simple substances like carbon dioxide and water. Biofilters generally are used
to cleanse the air exiting the building through exhaust fans. Biofilters have
only been efficient at treating low concentrations of odorants from building
fans. Most biofilters require fans that are capable of providing a good flow of
air at a high static pressure. As the filter bed ages, the peat or other filter
material will become more compact and will need to be stirred. It is a difficult
task to design a system in which the biofilter is "transparent" to the
building’s operation.
Another variation of the biofilter is a biomass filtration system. This
system draws air through crop residue, such as baled straw or hay to remove some
of the dust, thereby removing some of the odor. This is a new approach that has
only begun to be tested but is showing promise.
Industrial odor control has long utilized more exotic techniques such as
scrubbers and catalytic converters. While today’s scrubber technology is well
developed and versatile for industrial uses, the commercial units are generally
not cost effective for odor and dust control in livestock production facilities.
However, there may be some possible uses for a more simple, direct approach to
scrubbing exhaust air from a fan. A big challenge is to design a scrubber system
that utilizes recycled process water and is affordable. If the water used to
clean the air in a wet scrubber can be treated and recycled, it would help the
acceptance of this technology. The cost of using fresh water and the storage of
the process water may be prohibitive.
Catalytic converters are commonly used on internal combustion engines to
reduce odors and toxic emissions, but like scrubbers, are not typically cost
effective for livestock production facilities. Work at several locations,
including the University of Illinois are looking at options such as a catalytic
air cleaner to place in the ventilation system of an existing animal production
facility to reduce odors, and the use of catalytic "odor-eaters" that could be
placed inside animal confinement facilities to absorb odor-causing compounds.
Odor from manure storage
A second source of odor from livestock production is manure storage.
Bacterial action causes manure decomposition, which generates odors. These odors
are then released to the atmosphere if nothing is done to contain them. A number
of factors impact the bacterial action that breaks down manure. Moisture is
needed for bacteria to function; so dry manure (under 40 % moisture) is usually
less odorous than liquid manure. Temperature also has an impact on manure odors.
Higher temperatures speed microbial action, resulting in faster decomposition of
the manure. Also important is the type of bacteria present that is primarily
dependent on the presence or absence of oxygen in the manure. Aerobic bacteria
live when oxygen is present. Water and carbon dioxide are the products of manure
degradation by aerobic bacteria. Anaerobic bacteria work in the absence of
oxygen, which is the status of most manure storage structures. The products of
anaerobic bacteria degradation of manure are much more odiferous than the
products from aerobic bacteria.
Manure in buildings
Deep manure storage pits under livestock buildings are another source of
odors. These odors are primarily generated by bacterial decomposition of
accumulated manure. There are two basic methods of reducing odors in buildings
from such storage pits. The first is a good pit ventilation system that removes
the gases and odors generated from manure in the pit. Such a ventilation system
can also pull dust particles from the building down into the pit where those
particles may become trapped in the pit liquids. This method may reduce odor
within the building but may cause odor problems in surrounding areas. The second
method is to use shallow pits that are cleaned at least every 2 to 3 weeks. This
removes the manure from the building so that when degradation occurs, the odors
and gases generated are released into the atmosphere rather than accumulated
within the building. After the manure is removed, 2 to 3 inches of water should
be added back into the pit to decrease ammonia production
Size
Size obviously has an impact on odor. Larger operations generate more manure,
which may generate more odor. This has been a concern about larger livestock
production units that have been built. However, there are management techniques
that may help reduce some of the odor generated. One technique is to remove
manure as frequently as possible, thus decreasing the opportunity for
decomposition. Fresh manure is less offensive than decomposing manure; so
decreasing storage time of the manure lessens odors. Frequent removal also
usually removes more solids, the portion of manure generally responsible for
odor production. However, it is a problem to have land available for continuous
spreading of manure. If such land is available, this technique is a good option.
But in areas where crops are growing on the land for a considerable part of the
year, frequent spreading is not possible.
Lagoons
Lagoons are much different than "true" storage facilities. In addition to
storage, treatment also takes place in a lagoon. Lagoons are much larger than
traditional storage structures because the manure must be diluted with 6 to 10
times as much water as manure added. This dilution is necessary for proper
bacterial decomposition of the manure. Odor intensity from lagoons is usually
less than from typical slurry storage facilities, and aerobic lagoons have much
less odor than anaerobic lagoons. Although lagoons are not free of odor, odor is
seldom a problem if the lagoon is managed properly. An exception is late spring
and early summer, when warmer weather causes increased decomposition. During the
cooler weather of fall and winter, bacterial activity decreases and less manure
solids are broken down. Since the amount of manure added to the lagoon generally
remains the same throughout the year, the amount of undigested manure
accumulates during the cooler weather. When the weather warms and bacterial
activity increases, there is a large amount of manure solids to be broken down.
The rapid breakdown of this large amount of accumulated manure generates more
intense odors than normal, which can be offensive.
Management effects
Mismanagement of lagoons can cause increased odors throughout the year. In
addition to having enough dilution water, it is also important to release
consistent amounts of manure frequently into the lagoon. This allows the
bacterial population to stabilize and break down the manure as it is added.
Adding too much manure at one time, or at infrequent intervals, causes a
situation called "shock loading" which is similar to the spring warm-up, when
too much manure is available for decomposition at one time. This procedure
really starts with proper sizing of the lagoon. If the lagoon is too small, a
similar effect is seen as adding too much manure at one time or not having
enough dilution water. The lagoon must be large enough for adequate dilution of
the manure added to have proper decomposition without excessive odor production.
Operations that add production facilities that release manure into a previously
constructed lagoon may be asking for trouble if the lagoon is not large enough
to properly break down the additional manure. An important aspect of proper
lagoon start-up is that adequate water be in the lagoon before any manure is
added. The lagoon should have 1/3 to 1/2 of the minimum design level to ensure
adequate manure dilution to properly start the manure degradation process.
Lagoons should also be started during warm weather when bacteria are more
active.
The solids' component of livestock manure is of primary interest in lagoon
function because the solids' component contains the organic matter that is
broken down by bacteria. Therefore, the solids are ultimately the source of
odors. If the amount of solids released into a lagoon is reduced, odor
production should also lessen. One method of reducing the solids in a lagoon is
to separate the solids from liquids before the liquids are released into the
lagoon. There are a number of processes by which this can be done, including
mechanical processes or simply gravity in a settling basin or tank. Separation
works well for bovine manure but is more difficult with swine. Some chemicals
may work well in separating solids from liquid in swine manure.
Possible solutions
Odors from storage structures can become a problem when wind blows across the
liquid surface and odors are allowed to escape from the storage structure. This
is especially a concern with lagoons, which have large surface areas exposed to
the atmosphere, thus allowing plenty of opportunity for odor release. One method
of reducing the odor escape is to cover the storage structure. This is easier
done with some structures than others. Concrete structures may actually be
capped, so the structure is totally enclosed. Other structures may be covered
with materials such as large tarps. Another product is an oil based film that
spreads over the entire surface. The key to success of this process is to
decrease the interaction of the liquid surface with the atmosphere. To be
effective the cover must maintain coverage of the liquid surface in order to
decrease the chance of the atmosphere picking up odors and spreading them.
Another technology for managing odor is the use of synthetic lagoon covers
which has the added potential to capture gases produced during the treatment
process. 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 swine farms in California and elsewhere, reducing
energy costs and odor. Unfortunately, an economical system for producing biogas
from livestock manure has so far proved elusive except for larger operations. A
number of problems have been reported, including the overprotection of ammonia,
and methane generation has generally been unreliable, in simple systems using
covered lagoons. Because of the relatively low prices for petroleum, demand for
alternative energy sources has dwindled since the 1970s, making biogas less
cost-effective.
A similar concept is a floating biological cover. A simple example of such a
cover is the crust that forms on the surface of dairy manure in storage. Such a
crust was found to decrease the odors emitted from the storage structure. Covers
similar to the dairy crust are made of biological materials that will decompose
over time and can be mixed with the manure and applied to land. One example of
such a material is a layer of straw. The bio-cover reduces interaction between
the liquid surface and the atmosphere. One problem with floating bio-covers is
that they will sink after a while and therefore must be replaced. One possible
solution that has been suggested is to add mineral oil to the biological
material as it is blown out on the surface.
Aerobic treatment
One treatment method that does reduce odor if conducted appropriately is
aerobic treatment. This process involves adding enough oxygen to the manure so
that the aerobic bacteria can live and break down the manure. As stated
previously, the products of aerobic digestion are generally carbon dioxide and
water, two compounds without much odor. One major concern with this method is
the need to be sure adequate oxygen is added. There are several procedures
available or being developed to accomplish this. One method is to install a
surface aerator that incorporates air into the manure, either with windmills or
electric motor driven aerators. A second method is to release oxygen into the
manure. There are a number of ways being developed to do this, including
bubbling oxygen below the manure surface. A second major concern with aerobic
treatment is the cost required to apply the treatment. The process does work if
conducted properly, but it is an expensive alternative. Another speculation is
to combine both surface aeration and bacterial additives to control odor.
Additives
There are a number of products that have been proposed as solutions for
reducing odors from manure storage structures. There has been little research to
support the odor reduction claims of these products, with most information being
testimonials from individuals. Some products are designed to cover up or offset
the odors that have been released into the atmosphere. Masking agents are one
class of products that have an odor that is stronger than the odor from manure.
The object is to cover the manure odor with a stronger, hopefully less
offensive, odor. Another class of products is counteractants, which work by
offsetting manure odor with another odor so that the two odors basically cancel
out one another, thereby reducing odor intensity. One difficulty experienced
with counteractants is knowing what odor to offset. With the great variation of
odors possible, it is difficult to know which odor to prepare for and thus what
product to use. Because of this, success has been variable and somewhat limited.
A third class of additives is deodorants. These products are to eliminate odor
from manure, either by preventing the escape of specific gases or by killing the
organisms that cause the odor. Enzymatic products are a fourth class of
additives. These products are supposed to alter the biological pathways involved
in manure decomposition. As with many of the other classes of additives,
success has been erratic and there is limited data. Much work is currently
being conducted at a number of universities to evaluate many different products
and the effectiveness of each at reducing odors, and under which conditions the
products work best. As a general rule, additives work best when used in
conjunction with other odor reducing techniques.
There have been several attempts to reduce manure handling odors by altering
the ration being fed or by the addition of specific odor reducing material, such
as sagebrush, mint oil and a sarsaponin extract of the yucca plant. Although the
data from these materials are not conclusive, they suggest that it is possible
to alter the odor of fresh manure; however, that change does not persist once
the manure undergoes anaerobic storage. A related approach to manure odor
control is to alter the feeding regime to achieve enhanced nutrient utilization.
This approach has a logical attractiveness in that if the amount of manure could
be reduced, there would be a reduced potential for the formation of odorous
compounds . The use of synthetic amino acids is being investigated and has been
reported to result in reduced nitrogen in the feces and urine. At this point,
the research is still in a preliminary stage and does not offer a clear
possibility to the pork producer as a technique to reduce his exposure to
potential odor problems. (Miner, 1995)
Karl Shaffer, a researcher at North Carolina State University, has reported
that modifying feed composition can help control livestock odor. He reports
by reducing the crude protein content of feed by 2-4 percent and adding
synthetic amino acids to balance the ration, nitrogen utilization is enhanced
and nitrogen excretion is reduced up to 40-50 percent. Dr. Shaffer indicates
the downside of this technology is the high cost of amino acids added to the
feed. (Farm Bureau, 1998)
Odor from land application
Many nuisance complaints due to odor occur just after manure has been applied
to agricultural land. Such spreading creates a large surface area of applied
manure to interact with the atmosphere. Fortunately, there are a number of
management practices that will reduce odor intensity and duration if conducted
timely and properly.
Use of tillage equipment to incorporate manure that has been surface applied
is one way to reduce the interaction of manure with the atmosphere, and thus
reduce odor. The sooner manure can be incorporated after spreading, the less
time there is for odor release. A similar technique possible with liquid manure
is to inject the manure below the soil surface with a knife or sweep assembly,
or incorporate it with a series of disks as the manure is applied on the soil
surface. This will be effective in reducing odor but may not be acceptable in a
conservation tillage program. When surface applying by irrigation or
broadcasting from a spreader, use of a low trajectory spread pattern decreases
mixing with the atmosphere and thus reduces odor release. Irrigation of stored
manure may cause more odor release than any other application technique.
Irrigation of liquid from the second stage of a lagoon is a more acceptable
alternative.
Another odor control method is to carefully select the time when manure will
be land applied. The basic consideration as discussed below is to be a good
neighbor. Careful timing can decrease the opportunity for neighbors to
experience the odor released. Avoid spreading just prior to weekends or holidays
when people are involved in outdoor activities. Give special consideration to
events planned at recreation areas near the land receiving the manure. Also pay
attention to the wind direction and avoid spreading on days the wind is blowing
toward neighbors or recreational areas. Time of day also has an effect. Morning
spreading is preferred because as the air warms it rises, promoting manure
drying and lifting the odor upwards for mixing and dilution in the atmosphere.
Avoid high humidity days or just before a rain because the humidity causes odors
to linger. If possible, it is best to conduct all land application of manure
within a short time period rather than to extend the task. This will decrease
the duration of odors.
Neighbor relations
Personal interaction with neighbors has very little to do with odor control,
but may be the most important part of avoiding complaints. Producers who
have a cooperative public attitude receive few odor complaints. Open
communication is important; hiding something generally arouses suspicion. Always
be courteous when dealing with neighbors, even if their requests are
unrealistic. Alert neighbors to plans for spreading manure and discuss any plans
they have for outside activities. One farmer uses post cards to notify neighbors
of proposed spreading. If they are planning an activity they are asked to call
the farmer. This gives the neighbors a feeling that they have some control over
the situation and it is not imposed without their consent. Another suggestion
has been to even offer a motel room to neighbors during times when odors will be
intense. The offer itself may be the difference between happy or unhappy
neighbors. All spreading activities should be documented so a record is
available in case a problem should develop. Determine the cause of any complaint
and work to correct it. Good public relations go a long way toward improving
acceptance of odors generated by livestock production.
Vegetated barriers (shelterbelts) for odor reduction
Shelterbelts have the potential to be an effective and inexpensive odor
control device particularly when used in combination with other control methods
as already discussed. The following discussion adapted from Tyndall (1994) will
briefly discuss the potential impact of vegetative barriers.
The potential of shelterbelts is really defined by the characteristics of
livestock odors. These characteristics are:
- Odor source at or very near ground level;
- Limited plume rise, due to certain weather conditions (i.e. temperature
inversions);
- Plume shows spatial and temporal variability;
- Plume may be of large aerial extent;
- Close proximity to critical receptors of odor (i.e. people).
There is compelling evidence that shelterbelts will work very well within an
agricultural landscape to provide odor control by affecting these
characteristics. Because the odor source is near the ground and the tendency of
the plume is to travel along the ground, vegetation of even modest heights (i.e.
20-30 ft) may be ideal for plume interception and disruption.
Shelterbelts can easily be designed as to fit the production situation and
expected/ experienced odor plume shapes. Also, depending on the shelterbelt
design and species used, they can deal with the temporal characteristics and
provide year round plume/aerosol interception.
There are be four primary ways that vegetated barriers can reduce livestock
odors; dilution of gas concentrations of odor into the lower atmosphere,
encouraging dust and other aerosol deposition by reducing wind speeds, physical
interception of dust and other aerosols, and by way of acting as a sink for the
chemical constituents of odor. Each of these will be discussed briefly below.
Dilution of gas concentrations of odor into the lower atmosphere
Shelterbelts create turbulence at the surface of the terrain that intercept
and disrupt odor plumes traveling in laminar flow helping to push the plume into
the lower atmosphere facilitating dilution. In addition, lowering wind speeds
over storage lagoons can reduce convection of odorous compounds from the surface
and allow for slower release of the odor plume which also facilitates dilution.
Encouraging dust and other aerosol deposition by reducing wind speeds
Pesticide drift mitigation research suggests that due to reduced wind speeds
drift pesticide will drop from the air stream. In broadleaf species, downwind
drift reductions of 70% (no leaves present) to 90% (with leaves present) have
been recorded. Numerical simulation of the effects of tall barriers around
manure lagoons predicted reductions in downwind malodorous lagoon emissions of
26% to 92%. Wind tunnel modeling of a three-row shelterbelt system has
quantified reductions of 35% to 56% in the downwind mass transport of odorous
particulates (dust and aerosols).
Physical interception of dust and other aerosols and the vegetation as a sink
Researchers suggest that the forest cleans the air of microparticles of all
sizes by combing out twentyfold better than barren land. Leaves with complex
shapes and large circumference to area ratios collect particles most
efficiently, indicating that conifers may be more effective particle traps than
deciduous species as well as having an "in leaf" temporal advantage. Volatile
Organic Compounds (VOC’s) have a distinct affinity to the lipophilic membrane
(the cuticle) that covers plant leaves and needles. Researchers have quantified
measurable quantities of anthropocentric VOC’s that have accumulated at the
surface of plants (adsorption) and within the plants tissues (absorption).
Micro-organisms dominate the surface of plants. These organisms also adsorb and
absorb VOC’s and provide additional surface area for pollution collection. As
well as acting as a sink, these organisms also have the ability to metabolize
and breakdown VOC’s.
Conclusion
Livestock production does produce odors, and there is no way to eliminate
those odors entirely. The severity of those odors is dependent on the frequency
and duration of occurrence and the intensity of the odor, in addition to the
perception of the people experiencing the odor. Everyone’s perception is
different, as what may be a nuisance to one person may be pleasant to another.
Fortunately, there are a number of management practices that can be implemented
to reduce odor problems. The most important of these is general cleanliness of
animals and buildings. Frequent manure removal also decreases odors, as some
odors are generated while manure decomposes. Proper site selection for
production facilities is also important, with distance from neighbors one of the
most important factors. Increased distance from neighbors may be the easiest and
most appropriate method to minimize odor complaints. Many products are being
developed and promoted to reduce odors released from production facilities and
manure storage units. However there has been little research to support the use
of such products. Careful selection of when to apply manure to agricultural land
and use of practices such as injection or incorporation of manure goes a long
way toward reducing odor complaints. Open communication and cooperation with
neighbors develops good relationships, decreasing complaints and promoting
acceptance of livestock production.
References
Harmon, Jay D., "Odor Assessment and Control," Environmental Issues in
Livestock Production Home Study Course Agriculture and Biosystems Engineering,
and Gene Tinker, Extension Swine Field Specialist, Iowa State University, Ames,
IA. (Undated)
Zhang, Yuanhui , "Livestock Odor Research in Illinois," University of
Illinois, Department of Agricultural Engineering, Urbana, IL (Undated)
Miner, J. Ronald,
An Executive Summary, A Review of the Literature on the Nature and
Control of Odors from Pork Production Facilities, The Odor Subcommittee of The Environmental
committee of The National Pork Producers Council, Des Moines, IA 1995
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