 (Materials & methods
to ensure quality compost)
temperature
In aerobic composting
proper temperature is important. Heat is released in the process.
Since composting material has relatively good insulation
properties, a composting mass large enough (3’ x 3’)
will retain the heat of the exthermo-biological reaction and high
temperatures will develop.
High
temperatures are essential for destruction of pathogenic
organisms and
undesirable weed seeds. Also, decomposition is more rapid in the
thermophilic
temperature range. The optimum temperature range is 135° -160° Fahrenheit.
Since few thermophilic organisms actively carry on decomposition
above 160° F, it is undesirable to have temperatures above this for
extended periods.
Eggs
of parasites, cysts and flies have survived in compost
stacks for days when the temperature in the interior of the stack
is around 135° F. Since a higher temperature
can be readily maintained during a large part of the active composting
period, all the material should be subjected to a temperature of
at least 150° F for safety.
Sometimes compost operators avoid prolonged high temperatures because
the nitrogen loss is greater at high temperatures because ammonia
vaporizes, which takes place when the C:N ratio is low. But there
are other ways of minimizing nitrogen loss than operating at a lower
temperature. The advantages of destroying pathogenic organisms and
weed seeds, controlling flies, and providing better decomposition
outweigh any small nitrogen loss due to high temperatures.
A drop
in temperature in the compost pile before material is stabilized
can mean that the pile is becoming anaerobic and should be aerated.
High temperatures do not persist when the pile becomes anaerobic.
The temperature curve for different parts of the pile varies somewhat
with the size of the pile, the ambient (surrounding) temperature,
the moisture content, the degree
of aeration, and the character
of the composting material. To maintain high temperatures
during decomposition, compost must be aerobic. The size of the compost
pile or windrow may be increased to provide higher temperatures in
cold weather or decreased to keep the temperatures from becoming
too high in warm weather. Experience shows that turning to release
the heat of compost piles, which have become so hot (170°-180° F.)
that bacterial activity is inhibited, is not very effective. When
the material is actively decomposing, the temperature, which falls
slightly during turning, will return to the previous level in two
or three hours. Also, it is impossible to bring about any significant
drop in temperature by watering the material without water logging
the mass.
Variations in moisture content between 30% and 75% have little effect
on the maximum temperature in the interior of the pile. The initial
temperature rises a little more rapidly when the moisture content
is 30% to 50% than when it is 70%. Studies show an important and
significant correlation between the moisture content and the temperature
distribution within the pile. When moisture content is high, temperatures
near the surface will be higher, and the high temperature zone will
extend nearer to the surface than when the moisture content is low.
For example, in experiments at University of California during mild
weather when the air temperature fluctuated between 50° and 80° Fahrenheit,
the zone of maximum temperature in a pile with a moisture content
of 61% extended to within about one inch of the surface while the
maximum temperature zone in a pile containing 40% moisture began
6 inches below the surface.
Deeper piles caused higher temperatures and better temperature distribution,
and subject more material to a high temperature at any one time.
Hence, the actual mass of the material evolving heat is important
in providing adequately high temperatures.
Shredding
or pulverizing feedstock also provides better temperature distribution and less
heat loss.
Materials with a high C:N ratio or
containing large amounts of ash or mineral matter usually attains
high temperatures more slowly in the compost pile.
Aeration to maintain aerobic conditions in the compost pile is essential
for high temperatures. When the
compost pile becomes anaerobic, temperature drops rapidly. Even small
areas which have become anaerobic will often exhibit a lower temperature
than surrounding aerobic material. |
