Composting is the biological decomposition and stabilization of the biodegradable component in organic matter under controlled conditions. It is an aerobic process (requires oxygen) and is carried out by microorganisms which metabolize organic waste as an energy source. The effectiveness of the process is dependent upon the environmental conditions present within the composting system.

The composting process is directly affected by oxygen, temperature, moisture, material disturbance, particle size, surface area, physical properties of the wastes and the size and activity of microbial populations. Litter that is too fine will limit the oxygen supply to the microorganisms and growth will be significantly reduced. Slower microbial growth results in lower composting temperatures. At a temperature of 155 degrees F, carcasses will decompose about twice as fast as at 130 degrees F. Smaller carcasses, or those which have been ground will require less time to stabilize than large, whole carcasses.

The essential elements required by the microorganisms are carbon, nitrogen, oxygen and moisture . If any of these elements are lacking, or if they are not provided in the proper proportion, the microorganisms will not flourish and will not provide adequate heat. A composting process that operates at optimum performance will convert animal carcasses into a stabilized material that is odor and pathogen free, and a poor breeding substrate for flies and other insects. In addition, it will significantly reduce the volume and weight of organic waste as the composting process converts much of the biodegradable component to gaseous carbon dioxide.

Composting is already an acceptable method of recycling organic wastes and is rapidly becoming a preferred alternative for stabilizing and sanitizing animal carcasses. The cost associated with set up and maintenance of an animal carcass composting system is relative low.

METHOD
The composting method is determined by individual requirements and animal mortality rates. Several methods including aerated windrow, static pile and in-vessel (bin) are currently in use.

For smaller operations, where the mortality rates are relatively low, a single stage composter may suffice. It can be constructed using 4' × 4' pallets fastened together to form a box and lined with wire mesh.. One side should be detachable to facilitate loading, mixing and unloading. The composter should be waterproof and located in and area that is protected from the wind.

For larger operations where the mortality rates are higher, a two stage or three stage composter may be required. The size of the bins is dictated by mortality rates. The bins should be constructed to facilitate loading, mixing and unloading and should be waterproof and located in an area that is protected from the wind.

In-vessel composting is a relatively low management alternative to static-bin composting. In-vessel mechanical composters can be constructed using a rotating drum designed to turn at the rate of three to five revolutions per hour. This configuration will decompose and stabilize animal carcasses in three to eight days.

ODOR
For optimum odor control the blended material should have a pH at or slightly below neutral. Odors can also be eliminated by inoculating the mixture with CBPA stock solution (CBPA concentrate mixed with water at a rate of 1:200).

COMPOSTING PERIOD
The time required to compost animal carcasses is directly proportional to the size of the carcass and the composting method. For example, in-vessel composting can stabilize smaller carcasses in three to eight days while windrow composting may take 21-28 days.

TEMPERATURE
Temperature is the primary indicator of biological activity within the compost pile, and is easily measured with the aid of a digital thermometer and a probe. Moisture content, oxygen availability, and microbial activity all influence temperature.

When the temperature within the composter continues to increase, the composting process is operating at optimum performance. When the temperature peaks and begins to decrease, the pile should be turned. Turning introduces oxygen into the pile and causes the temperature to rise. Turning should continue until the temperature fails to rise. This indicates that the compost material is biologically stable. Sustained temperatures above 130 degrees Fahrenheit favors destruction of pathogenic bacteria, viruses, fly larvae and weed seeds that might be present in the waste.

When conditions within the pile change due to an unfavorable moisture content, change in the C:N ratio, or a decrease in oxygen supply, the temperature may drop and the microbial population will shift back to a regime of lower temperature microbes, causing the compost pile to go anaerobic.

AERATION
Aeration in the composting process is critical. Proper aeration introduces oxygen and evacuates excess heat, gas and moisture. As oxygen becomes depleted, microbial growth will slow and the temperature of the mass will decrease. Proper aeration may be achieved by passive air exchange, forcing air through the material or mechanical turning. In addition, aeration minimizes nitrogen loss by denitrification.

C:N RATIO
The carbon / nitrogen ratio (C:N) directly affects the composting process. C:N ratios of 15:1 to 30:1 are acceptable. If however the C:N ratio is less than 25:1, the microorganisms cannot metabolize all of the available nitrogen, and it is lost as ammonia. This may result in unpleasant odors, and loss of fertilizer value. When the C:N ratio exceeds 30:1, the composting process slows down.

MOISTURE
Moisture content is critical to the composting process and determines whether the process will be "aerobic" (with oxygen) or "anaerobic" (without oxygen). For animal carcass disposal, aerobic composting is preferred because it is faster and produces less odors. Ideal moisture content for aerobic composting is about 40 - 50 percent. When the moisture content reaches 65 percent, the process begins to go anaerobic. High moisture level can be controlled by adding bulking agents to the mixture. Low moisture contents are increased by sprinkling the pile with CBPA STOCK SOLUTION (CBPA concentrate mixed with water at a rate of 1:200).

SUMMARY
Managing the composting process is relatively easy and is not labor intensive. Daily labor requirements for operating a poultry carcass composter designed to handle 1000 pounds per day is about thirty to forty minutes. This includes loading, turning, monitoring and unloading. Managed properly, composting can be an odorless, disease free, environmentally friendly process that produces a value added product suitable for use in numerous fertilizer applications.