Human and livestock pathogens and their control during composting
Muriel Lepesteur
Abstract
Compliance with current guidelines for composting based on time-temperature requirements does not always translate into safe compost products. This review’s objective is to assess what pathogens are inactivated during composting and how inactivation could be improved to address that issue. While most pathogens are inactivated by the heat generated during composting, spore-forming bacteria and Group II viruses are likely to survive the process. Other bacteria may also survive the composting process and regrow. Reports of protozoa and helminths inactivation are contradictory due to the lack of cheap and reliable technologies to ascertain their viability. Other factors contribute to pathogen inactivation by promoting the activity of beneficial microorganisms that produce antimicrobial compounds, compete for nutrients or prey on pathogens. Volatile acids are effective against bacteria and viruses by targeting their envelope (if any) and their genome. Ammonia affects most pathogens including Ascaris eggs and exhibits a strong effect against ssRNA viruses. Future research should focus on better understanding the role of the batching recipe and mesophilic and maturation phases in inactivating pathogens. Understanding how pathogens present in a feedstock are inactivated is also crucial to predict what factors are important and optimize the composting process. More appropriate indicators should be used for high-risk wastes containing human or animal wastes. Enterococci have been suggested as an additional indicator but the relation between the presence of enterococci or other indicator and the survival of other types of pathogens should be further investigated.