Developing and Testing a Framework to Measure the Sanitation Efficacy on a Random Particle Level in Composting Industry Open Access
- Other title
- Type of item
- Degree grantor
University of Alberta
- Author or creator
- Supervisor and department
McCartney, Daryl (Civil and Environmental Engineering)
- Examining committee member and department
Neumann, Norman (School of Public Health)
Felske, Christian (City of Edmonton)
Clark, Grant (Bioresource Engineering, McGill University)
Bouferguene, Ahmed (Campus St. John)
Yang, Liu (Civil and Environmental Engineering)
Buchanan, Ian (Civil and Environmental Engineering)
Department of Civil and Environmental Engineering
- Date accepted
- Graduation date
Doctor of Philosophy
- Degree level
Both direct and indirect process validation regulations are being used to ensure the safety of compost products. The North American guidelines specify upper limits for certain pathogenic and indicator microbes, which are presumably achieved by exposing every particle of compost to temperatures ≥55°C for at least 3 consecutive days. Regardless of maintaining high temperatures, there may still be pathogenic microorganisms that survive composting. Hypothetically, this could be because: (1) temperature test methods may not account for spatial and temporal temperature variation in large composting piles, giving the false impression the temperature-contact time condition has been met; and/or (2) the existing temperature contact time criterion may be inadequate.
A temperature probe was developed consisting of a temperature recording circuit and inoculum holder (i.e., cryovial) enclosed in a cylindrical case made of anodized aluminum. Two field trials suggested that this probe behaves like a random particle in compost. Both trials also showed that the aluminum case protects the probe’s circuitry and the cryovial from various physical and chemical stresses.
The temperature probe was used to develop a temperature sampling framework for the indirect process validation. It suggested that in a covered aerated static pile the likelihood for a random compost particle to reach and maintain ≥55°C for at least 3 consecutive days varies between 76 – 93% and could increase to 98% after five pile turnings. Typical cool zones mostly remained at ≤45°C, resulting in questionable thermal inactivation responses for pathogenic microorganisms.
A direct technology validation framework using the temperature probe was developed and proposed. Two experimental runs demonstrated that samples in which temperatures ≥55°C were maintained for at least 3 consecutive days were free of culturable Salmonella sp., Escherichia coli sp., and phi-S1 bacteriophage. However, a sample that remained in the cool zone throughout one experiment run still had culturable Salmonella in appreciable amounts thus reiterating the importance of cool zones in the sanitation process. Molecular analysis of the samples demonstrated that a gradual increase in compost temperature induced a potential viable but not culturable state in Salmonella and E. coli. It was concluded that the specified time-temperature conditions are likely adequate but more research is needed to study the behavior of VBNC pathogens in compost.
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