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The relationship between temperature regime and pathogen kill in composting and assessing exposure of compost workers to airborne biohazards Zhang, Xi


The study has been conducted in three parts: I. Collect both temporal and spatial thermal data; 2. Quantify the number of organisms of interest in compost samples; 3. Collect and analyse bioaerosol samples to test the workers’ exposure to organisms of concern. The study obtained more detailed and extensive data of both spatial and temporal temperature distributions in real, operational compost piles than any previous studies. By using data loggers allocated at every part of the pile (approximately surrogate of each 0.5 m3 material) and continuously record temperatures from building the new pile till screening. A series of findings have been achieved from the intensive temperature monitoring, such as how differently material at different positions could behave in terms of temperature; how physical parameters (particle size, porosity etc.) of the material could influence the process and so on. Furthermore, the study also correlated the time-temperature regime with level of pathogen-kill for a full-scale operational composting practice. Total coliforms, Thermo-tolerant coliforms, E. coli and Enterococci were confirmed and quantified. Significant destruction of microbial organisms was observed during composting based on the performance of Enterococci. Some limitations about the test methods have been found. Also, some other factors such as temperature fluctuation, occurrence of re-growth, interference of environmental organisms etc. all made the composting microbiology a complex issue. Besides studying the bacteria in the pile, effort has also been given to investigating exposures of how the airbome bacteria from handling the compost to workers at the site. It has been found that the cab can well protect the workers from being exposed to the bioaerosols; precipitation could significantly reduce the number of airborne bacteria; turning and screening the pile do result in relatively high concentration of bioaerosols while the influence on upwind and downwind area from composting facility is negligible; also the presence of airborne bacteria does show some consistency with the performance of bacteria in the feedstock over time. In addition, moisture content and nutrients (C, N) concentration analysis were determined on the compost samples. The weather conditions had been monitored continuously during the whole process.

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