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Hog Manure odor Control
DANGEROUS GASES
& ODORS FROM HOG FACILITIES
Methane, Carbon Dioxide, Ammonia, Hydrogen Sulfide
Generally, gases and odors produced
in close confinement hog facilities are the result of
bacterial action on biodegradable parts of hog waste.
Gases produced in greatest volume are methane, carbon
dioxide, ammonia and hydrogen sulfide.
There is also a complicated group
of volatile organic compounds that contribute to the
odor. These substances include amines, mercaptans,
alcohols, carbonyls and sulfides in trace amounts.
Methane, the gas produced in
greatest volume during the decomposition process, results
from organic acids being degraded. This gas usually
escapes to the atmosphere and is a potential air
pollutant.
Carbon dioxide is the second
most
abundant gas produced as organic acids are degraded.
Because it is odorless, the pollution potential of this
gas is often overlooked.
Ammonia is released as amino acids
in protein are broken down by bacteria. This gas is
easily recognized because of its pungent odor.
Hydrogen sulfide is also a part of
the odor. Anaerobic reduction of sulfur-containing
compounds such as certain amino acids result in formation
of hydrogen sulfide. This gas has a very offensive odor.
Properties
and effects of noxious gases
Methane is colorless, odorless and
lighter than air and is formed by a highly specialized
group of bacteria. Generally, conditions found in close
confinement hog facilities are not conducive to producing
significant amounts of methane. Methane has an explosive
characteristic and an asphyxiating effect.
Carbon dioxide is colorless,
odorless and heavier than air. It normally makes up 30 to
60 percent of the gas resulting from decomposition of hog
manure. Generally, concentrations of carbon dioxide
greater than 4 percent are cause for concern for both
humans and livestock.
Ammonia is a colorless gas, that
makes up a very small percentage of the gases produced
during decomposition of animal manure. It is easily
recognized by its pungent odor. Ammonia concentrations
greater than 0.01 percent in a confinement building are
likely to cause considerable discomfort to both humans
and animals. Ammonia is highly soluble in water,
therefore its presence usually is less noticeable where
liquid manure systems are used rather than solid floors.
Hydrogen sulfide is colorless, and
has the characteristic "rotten egg" smell. It
is given off in relatively small quantities during
decomposition of hog manure. Hydrogen sulfide is the most
toxic of manure gases. Concentrations of this gas greater
than 0.001 percent cause considerable discomfort to
humans and livestock. Levels greater than 0.05 percent
are likely to be lethal.
Potentially
lethal conditions
Under normal conditions,
there is little likelihood of noxious gas levels rising
to critical concentrations in a well-designed confinement
facility. However, there are circumstances in which gas
levels can become critically high, even when the facility
is properly designed.
Ventilation breakdown is most often
the cause of critically high gas levels in confinement
facilities. If fresh air in a confinement facility is not
replenished due to power failure, carbon dioxide levels
can reach lethal proportions in eight to 10 hours. Death
under these circumstances is usually hastened by rising
temperature and humidity in the confinement facility.
Agitating manure that has been
stored in a pit for several months can release dangerous
quantities of noxious gases, even if the ventilation
system is operating properly. The dangers during
agitation are release of the highly toxic gas hydrogen
sulfide and release of carbon dioxide in quantities
sufficient to deplete the oxygen supply.
Entering a manure storage pit can
be potentially lethal for humans. Carbon dioxide and
hydrogen sulfide are heavier than air and tend to collect
at the manure surface. In pits equipped with a cover or
manhole opening only, methane can accumulate, creating
potentially explosive conditions. Persons should never
enter a manure storage pit unless it has been ventilated
to get rid of dangerous gases.
GUIDELINES
FOR CONTROLLING GASES & ODORS IN CONFINEMENT BUILDINGS...
Remove manure from the
building regularly. If manure is removed from a
building before it begins to decompose, only
small amounts of gases and odors are released.
Buildings equipped with pits
should have venting portals between the manure
level in the pit and the slats above the pit.
Maintain water level in manure
pits to collect soluble gases.
Keep the ventilation system in
top operating condition.
Provide for auxiliary power
supply to operate the ventilation system in case
of power failure.
Use extreme care when
agitating a manure pit or starting the rotor of
an oxidation ditch in which manure has collected
for several days.
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