Mortality Composting and Pathogen Reduction

The traditional approach to mortality composting does not provide acceptable pathogen reduction capabilities when dealing with Specific Risk Material

Composting by its very nature is not a very homogenous process and for this reason composting of Specific Risk Materials does not offer a truly reliable method of pathogen destruction.

Multiple mechanisms are known to be involved in the inactivation of pathogens during composting. These methods may include exposure to heat, microbial antagonism, antibiotic production, parasitism, organic acid and ammonia production,competition for nutrients and substrate selectivity. Temperature is traditionally considered the most important factor in pathogen inactivation, and it is relatively easy to measure temperature during any process with compost being the exception due to variance in substrate make-up, density and porosity issues, moisture content and so forth. All these factors determine how heat is distributed and retained within a specific macro and micro regions of a compost pile.

Whilst the thermal death point and environmental sensitivity of many pathogens are well known, it is appropriate to consider some of the specific pathogens and issues of relevance specific to mortality composting.

Composting is a well-established pathogen reduction method. It is known to reduce a large percentage of pathogenic viruses, bacteria, fungi, protozoa (including cysts) and helminth ova to reasonably low levels. There are unfortunately some serious limitations to the composting process. Traditional composting methods do not effectively control, eliminate or in some instances not even produce a noticeable reduction in certain very serious and very common pathogens.

Examples of these pathogens are the endospore-forming bacteria (e.g. Bacillus anthracis - Anthrax, Clostridium botulinum - Agent causing Botulism) and prions such as Transmissible Spongiform Encephalopathy (TSE), Bovine Spongiform Encepalopathy (BSE), Scrapie and other prion related diseases.

Prions are highly resistant to both physical and chemical means of inactivating pathogens and for this reason it is generally accepted that composting alone will be ineffective in reducing infectivity of prion or endospore-forming bacteria-infected carcasses or tissue.

Mortality Composting and Pathogen Reduction

The traditional approach to mortality composting does not provide acceptable pathogen reduction capabilities when dealing with Specific Risk Material

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