After a bin is filled, the compost must undergo a primary heating cycle of 60 to 90 days. This time frame varies based on the size of mortalities placed in the bin.

After this initial heating cycle, the partially composted carcasses are moved from the primary bin to a secondary bin.



“Moving the compost breaks up the materials in the pile, redistributes excess moisture and introduces a new oxygen supply,” Glanville said.

“By the end of a 60- to 90-day secondary heating cycle with additional decomposition activity, even large carcasses of breeding stock are normally reduced to a few large bones that are free of soft tissues which cause odors or attract insects and predators.”



The composting process can continue during winter months, he said.

The layout of the composting facility also plays an important role. By having bins share a larger amount of common wall area, it cuts down on the amount of bin wall exposed to the cold, reducing heat loss.

There is more information on composting equipment, facilities, procedures, sizing and layout in the ISU Extension publication, “Composting Swine Mortalities in Iowa,” https://store.extension.iastate.edu/ItemDetail.aspx?ProductID=5517, available from the Extension Online Store at www.extension.iastate.edu/store.



At the ISU swine farm, a nitrogen source (mortalities or manure) and a carbon source (typically corn stalks or woodchips) are the primary materials used in composting.

After the process is complete, the composted material is then usually applied on cropland.



“Land disposal of mortality compost adds organic matter to the soil and allows mortalities to be returned to the soil without odor, attraction of flies and other insects or scavengers,” Glanville said.



The long-term success of composting on the swine farms has led to similar practices at other Iowa State facilities, including the poultry and beef teaching farms.



“Deciding to compost means initial costs of constructing the facility,” Lampe said. “But in the long run, it saves money that would be spent on a potential disease break from vehicles such as rendering services or fuel trucks for an incinerator entering the farm property. The trade-off was been well worth it at the farm.”