Composting Basics

On-farm composting operations

Loading the composter

Mortality composting is begun by placing a 12-inch layer of dry cover material (sawdust, wood shavings, chopped corn stalk) in the bottom of the bin. Decaying carcasses will release excess moisture, so the absorptive base layer plays an important role in preventing release of excess liquid.

Carcasses should be placed on top of the base layer so that they do not touch each other and are at least 9 - 12 inches from bin walls. Too many carcasses in one spot leads to localized wet spots and poor decay. Carcasses that are too close to the cool exterior side walls of the bin will decay slowly and will not be exposed to the high temperatures that kill disease-causing microorganisms.

After a layer of carcasses has been positioned inside the bin, they are covered with 6 - 9 inches of sawdust or other cover material. Complete coverage with dry cover is important. Haphazard coverage can lead to fly, rodent, and scavenger problems. Daily layering of new carcasses and cover material continues until the bin is filled to a depth of about five feet. In some instances, it may help to segregate large and small carcasses into separate bins. This allows smaller carcasses to move through the treatment process quickly, minimizing the amount of bin space tied up in lengthy treatment cycles. To help insure good coverage throughout the composting cycle, it may be necessary to add cover material from time to time as material within the bins settles. This is particularly true when large carcasses are being composted.
Heating cycles

In a properly operating compost process, new material added to the bins reaches temperatures of 120 -150 degrees F within 24 to 48 hours. Internal temperatures can be monitored with a long-stemmed (36- 48 inch) composting thermometer like that shown in the adjoining pictures to insure that microbial activity is reasonably uniform throughout the composting bin. To obtain an accurate picture of internal conditions, be sure to probe the bin at several locations. It is not unusual to find hot and cool spots within the same bin, so a single temperature measurement can be misleading. If a bin fails to heat up, moisture excess or deficiency is the most common cause, and it may be necessary to unload the bin and mix in compost from an active (hot) bin.

During cold weather, use of warm and slightly moist cover material can speed development of desirable internal temperatures. Most cover materials generate heat as they undergo their own natural decomposition. If stored in sufficiently large piles that are protected from wind and rain, these materials often have internal temperatures of 100 - 140 degrees F. Again, use a long-stemmed compost thermometer to monitor cover temperatures, and use material from the interior of the stack when covering new carcasses added to the compost bin.

After a bin is completely filled, it must undergo a primary heating cycle that lasts about 90 days. The length of the primary heating cycle will vary with the size of carcasses placed in the bin. For farrowing and nursery losses, an intial heating cycle of as little as 30 days may be adequate. If the bin is filled primarily with larger market-weight animals or breeding stock, primary cycles as long as 6 months may be necessary.
During the primary heating cycle rapid microbial action depletes the oxygen within the bin, the rate of decay slows, and internal temperatures will decline. Following the primary cycle, the partially composted waste is removed from the primary bin and placed in a secondary bin. The mechanical action of moving the compost breaks up the pile, redistributes excess moisture, and introduces a new oxygen supply. Once this takes place, a secondary heating cycle occurs, accompanied by further decomposition. By the end of the secondary heating cycle, carcasses as large as 15–20 pounds are normally reduced to bones that are reasonably clean and free of soft tissues that cause odors or attract insects and predators.

Moisture control

Preventing excessive moisture content during rainy seasons, is one of the most important tasks in a successful composting operation. As noted in the section on Factors that affect composting, excess moisture can lead to slow decomposition and odor production.

To avoid excess moisture during rainy seasons, composting and cover material storage should be done under a roof or be covered with a tarp. To help avoid discharge of leachate (prohibited by IDNR rules), operations that are not covered should be carefully mounded to prevent ponding of water on top of compost or stored cover materials. If excessive moisture conditions develop, the quickest way to remedy this situation is to use a loader to mix wet material with drier material that has been protected from the elements.
More operating info

For additional details on composting operations, be sure to visit the Bilsland Farm Operating Data featured in our online Tour of Composting Facilties.