Wastewater (number/100 mL) Upwind (number/m3) Downwind (number/m3): 10-30 m 31-80 m 81-200 m a ND, none detected
81 46 25
0.01 ND ND
system where undisinfected effluent was applied to the land. It seems clear that the very low aerosolization efficiencies (E) as defined in Equation 3.27 for sludge spray guns and truck-mounted sprinklers indicate very little risk of aerosol transport of pathogens from these sources, and this has been confirmed by field investigations (Sorber et al., 1984)
Composting is a very effective process for inactivating most microorganisms, including viruses, due to the high temperatures generated during the treatment (see Chapter 9 for details); however, the heat produced in the process also stimulates the growth of thermophilic fungi and actinomycetes, and concerns have been expressed regarding their aerosol transport. The aerosols in this case are dust particles released when the compost materials are aerated, mixed, screened, or otherwise moved about the site.
A study was conducted at four composting operations involving 400 on-site and off-site workers (Clark et al., 1984b). The most significant finding was a higher concentration of the fungus Aspergillus fumigatus in the throat and nasal cultures of the actively involved on-site workers, but this finding was not correlated with an increased incidence of infection or disease. The fungus was rarely detected in on-site workers involved only occasionally or in the off-site control group.
The presence of Aspergillus fumigatus is due to the composting process itself and not because wastewater sludges are involved. The study results suggest that workers who are directly and frequently involved with composting operations have a greater risk of exposure, but the impact on those who are exposed only occasionally or on the downwind off-site population is negligible. It should be possible to protect all concerned with respirators for the exposed workers and a boundary screen of vegetation around the site.
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