The Effect of Green Waste Composting on the Concentration and Composition of Ambient Bioaerosols

The emission and dispersal of bioaerosols from commercial composting facilities has become an issue of increasing concern over the past decade, as historical evidence links bioaerosol exposure to negative human health impacts. As a result, recommended concentrations and risk assessment limits were imposed in 2001. However, more recent research has suggested that these limits may be exceeded under certain circumstances. For example, underestimation of bioaerosol concentrations may occur through „snapshot‟ sampling, and the use of methods that may reduce culturability of bioaerosols. This study aimed to address several gaps in knowledge, including quantification of bioaerosol concentrations downwind from sites, analysis of the effect that operational and environmental influences have on emission and downwind concentrations, and investigation of methods for the enumeration of non-culturable bioaerosols. The concentrations of bioaerosols upwind, on-site and downwind from two open-air green waste windrow composting facilities were enumerated in extensive detail, producing the first detailed and validated database of bioaerosol concentrations at green-waste composting facilities. The effects of composting processing activities, season, and meteorological conditions on concentrations were also investigated utilising this dataset. Results from these studies suggested that bioaerosols are able to disperse in elevated concentrations to distances beyond the 250 m risk assessment limit. Downwind peaks in concentration were directly linked to compost processing activities on-site, with the risk of sensitive receptor exposure to bioaerosols during non-operational hours minimal. Further, it was found that patterns in downwind concentrations of bioaerosols are likely to be governed by buoyancy effects, as a second peak in concentrations was found at 100-150m downwind. This finding was further supported through the use of a novel direct counting method. Finally, molecular methods allowed the composition of bioaerosols emitted from composting to be determined and showed that composting significantly alters the aerobiotic community at distances downwind. The methods investigated provide the potential for detailed, continuous measurements of bioaerosols, alongside identification of potentially pathogenic microorganisms, and could ultimately lead to source apportionment of bioaerosols.