Tom A. McCaskey, Joe A. Little, Rachel M. Krotz, Sarah P. Lino, and Todd C. Hannah

IN ALL COMMERCIAL SWINE OPERATIONS, it is common for a small percentage of animals to die during production. The disposal of dead pigs is a vexing task for swine producers, but AAES research has shown that swine carcasses can be composted on farms to produce a valuable fertilizer without generating offensive on-farm odors.

Composting has become common on poultry farms and is widely accepted by environmental agencies as a feasible, environmentally acceptable method for disposal of chicken carcasses. However, making this technology work with swine carcasses, which are larger than poultry carcasses, and controlling any odor problems during the composting process are legitimate concerns. An AAES study was conducted to determine the best composting techniques and to learn more about the problems or benefits associated with composting dead pigs.

Composting is a process through which microorganisms break down organic materials into a safe, stable humus. For composting to take place, several components are required. These include:
(1) The material being used for composting must be organic in nature (such as farm animal mortalities, animal manures, food wastes, etc.);
(2) The materials must be blended with carbon sources to achieve at least a 15:1 carbon-to-nitrogen (C:N) ratio of the compost mixture so that microorganisms can work;
(3) Moisture levels of the compost mixture should be adjusted to about 40%, which is favorable for microorganisms to degrade the organic material (carcasses);
(4) A bulking agent, such as poultry litter or recycled compost, is recommended to be added to the mixture to make the compost degrade more quickly and also generate heat that kills pathogenic bacteria, such as Samonella and E. coli, which might be in the compost.

The composting trials were conducted at the Lower Coastal Plain Substation in Camden. The composting ingredients consisted of: (1) recycled compost generated from previous composting studies, which was used as a bulking agent; (2) dead pigs weighing less than 15 pounds each; (3) chopped hay as a carbon source; and (4) water.

These ingredients were added in the wet weight ratio of 3:1:0.3:0.5, respectively (see Table 1). Based on this ingredient ratio, swine carcasses comprised 20.8% of the compost weight, and the compost mixture had a C:N ratio of 15:1.

Composting was conducted in wooden bins four feet square at the base and five feet high. A six-inch layer of recycled compost was placed in the bottom of the bin, followed by a layer of swine carcasses (mortalities), a layer of chopped hay, and water was added to the top of the layers. Each time swine mortalities were added to the bin, the layers were repeated until the bin was filled, resulting in about half a ton of ingredients. Finally, a six-inch cap of recycled compost was added to the top of the bin to control odors and vermin.

Temperature probes were placed in the bins to monitor the heat generated in the compost. For optimum composting, the compost temperature should reach at least 122°F and hold that temperature for five days to eliminate any enteric pathogenic bacteria.

After 30 days, the compost was removed from the bins, mixed for aeration, and returned to the bins to undergo a second 30-day composting process. After the composting process, samples were collected for N-P-K analyses. All analyses were conducted ona dry weight basis and performed in triplicate.

Four composting trials wer conducted, and all compost mixtures had the same ingredients in the same ratio. After first-stage composting, the weight of the compost mixture decreased an average of 13.5% and the volume decreased 16.9% (Table 2). After combined first- and second-stage composting, the weight and volume decreased a total of 22.1% and 21.8%, respectively. Most of the decrease occurred during first-stage composting, amounting to 61% for mass and 78% for volume. Weight and volume decreases are due in part to moisture loss and to volatilization of gases produced during degradation of the organic matter. When the composting process is complete, weight and volume will stabilize.

Based on the compost ingredient ratio of 3:1:0.3:0.5 (recycled compost:mortalities:chopped hay:water), the recycled compost (bulking agent) made up 62.5% of the compost mixture. During two-stage, static pile composting, the compost weight decreased 22%. If teh finished compost is recycled as a bulking agent, 80% of the compost weight generated in one compost bin of mortalities. This leaves 20% excess compost generated during each composting cycle.

The finished compost contains about 35% moisture, has no noxious odors, and contains (on a wet ton basis) about 50 pounds of N, 100 pounds of super-phospate, and 61 pounds potash (Table 3). Based on commercial fertilizer costs, the fertilizer value of a wet toon of the swine mortality compost was determined to be $47.

These results suggest that swine carcasses can be composted on farms without creating offensive odors and yields a valuable fertilizer, thus giving swine producers another way to turn a waste product into a valuable resource.

McCaskey is a Professor, Krotz is a Research Associate, Lino is a Research Specialist, and Hannah is a Research Assistant of Animal and Dairy Sciences; Little is Superintendent of the Lower Coastal Plain Substation.