Grinding and Screening Composted Bones
By Dale Rozeboom, Michigan State University
Mechanical screening and grinding of bones from finished mortality compost may be a future consideration.
All farm operators know that taking care of mortality is one of the responsibilities associated with managing the livestock farm. Whether these mortalities are due to natural causes, accident or disease, each one must be disposed of in an environmentally appropriate and biosecure way. In Michigan within the Bodies of Dead Animals Act (BODA) there are several carcass disposal options available under the BODA rules.
Among these methods, animal mortality composting has been gaining acceptance in recent years. Composting is a dynamic process where the carcass is enclosed in a mixture of plant or fiber rich materials such as wood chips, waste feed or used compost. Microorganisms in the mixture will utilize moisture, carbon and oxygen to break down the carcass tissues while releasing heat. Farm operators who use mortality composting ultimately discover that the larger bones of the animal carcass can take a considerable amount of time to be completely reduced. For older animals, significant decomposition of the bones may take 1 to 2 years
BODA rules state that "finished compost has no visible pieces of soft tissue and that the bones remaining at the time of final utilization shall be fully decomposed, or easily crumbled during the mechanical spreading process, or gathered and placed in a new batch of compost feedstock for further decomposition." This is not always possible with animals that were 6 months or older at death, and having undergone just 6 months of composting. On most farms, separation of bones from what would otherwise be finished mortality compost is a manual and undesirable job. Also undesirable, and a violation of BODA, is when mortality compost is spread on the fields leaving whole bones on the surface. They may become a neighborhood nuisance if displaced by pets and wildlife.
So, are there other alternatives for managing the bones resulting from the composting process? One possibility is to crush or grind partially-composted bones and then mix the small pieces back into the compost mix. Is there such equipment and is it affordable? Yes and possibly! For years, companies have been building machines to crush construction debris, recycle pavement and reduce gravel and this equipment could be applicable to bones filtered out of mortality compost.
At the 2013 Michigan Ag Expo the problem of dealing with residual bones from livestock composting will be discussed during a series of daily demonstrations hosted by Michigan State University Extension. Among the strategies that will be highlighted will be:
- Conditions in which bones can be field applied or buried.
- Screening bones from the finished compost and reincorporation into compost.
- Mechanical screening and grinding using the Allu™ bucket shredder.
These demonstrations will take place daily at 11 a.m. on July 16, 17 and 18 at the 2013 Ag Expo in East Lansing, Michigan. Sponsors for this demonstration are Cocoa, AIS, and Allu. For more details see the Ag Expo website.
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