Biosolids and Bioaerosols: The Current Situation

Biosolids – definition and usefulness:
Biosolids, better known as "sludge", come from municipal wastewater treatment plants or industrial processes, in particular pulp and paper mills and slaughterhouses. The particular characteristics of the biosolids vary depending on their origin (vegetable, animal, human) and the treatment process they have gone through (physicochemical or biological, aerobic or anaerobic digestion, lime stabilization, etc.). The agronomic and environmental benefits from the organic material and fertilizing elements contained in biosolids, essential for maintaining soil fertility, have been the subject of numerous scientific studies and have been extensively proven (N’dayegamiye, 2002 ; Simard et al.,1998).

The controversy – bioaerosols:
Land application of biosolids is giving rise to more and more apprehension, or even opposition, especially from people living next to application sites. This is seen in the United States and in Ontario in particular, and concern is expressed mainly in connection with municipal biosolids. The sometimes unpleasant, strong odor of certain biosolids, the greater visibility of this practice as a result of the increase in the amount of material applied and the public's growing suspicions regarding pathogenic organisms and their potentially negative effect on human health (following the Walkerton tragedy) are all factors that preoccupy the public (Crittenden, 2002 and 2001; OCAPS, 2001). Allegations of health problems caused in neighboring populations and linked to odors or to the presence of pathogens in municipal biosolids are reported in the media and in certain cases, result in legal action (Crittenden, 2002 ; Epstein, 2002). Some municipalities are taking steps to limit, suspend or even ban the application of biosolids in their territory. Among the risks associated with the presence of pathogenic micro-organisms in municipal biosolids, the release of bioaerosols during application has been raised by various opponents. Bioaerosols are airborne biological agents, which may contain pathogens. The controversy over bioaerosols also applies to the application of pulp and paper residuals (Thériault, 2001).

Conclusions:
The information consulted indicates that applying biosolids, particularly those originating from municipal wastewater treatment, may represent a potential source of airborne biological agents (bioaerosols). However, the scientific studies that we looked at indicate that the risks for exposed workers, such as farmers, are relatively low and even extremely low for people living in the vicinity of the sites where biosolids are being applied. Available information also suggests that the potential health risks are relatively lower than those associated with the management of manure. Thus the results of the study do not indicate the need for limits on applying biosolids that are more restrictive than those currently in force for biosolids in Quebec, in regard to pathogens and odours. Measurements of bioaerosol emissions linked to the recycling of manure and pulp and paper biosolids would however be welcomed, as the majority of studies had to do with municipal biosolids.


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