Land Application of Biosolids and the Risk from Human Pathogens: The American Experience

Pepper, I., and Gerba, C., The University of Arizona


In the United States, Class B biosolids routinely contain bacterial and viral human pathogens and yet 60% of this material is land applied. We have evaluated the risk of these pathogens in two ways. First, we
have conducted a national study on the incidence of pathogens and indicator organisms from wastewater
treatment plants across the U.S., and secondly we have evaluated risks from direct and indirect exposure
to these pathogens. For the study on the incidence of pathogens, thirty three samples of Class B
biosolids were obtained from wastewater treatment plants from across the nation. Biosolid samples
included cake (≃ 20% solids) and liquid biosolids (8% solid). Analyses included: fecal coliforms; E.coli
0157H7; Salmonella; Shigella; Clostridium perfringens; enterovirus; adenovirus; coliphage; and Ascaris.

This is the first nationwide study on pathogens in biosolids since the EPA Part 503 Regulations went into
effect, and provides a comprehensive database on the occurrence of pathogens in Class B anaerobically
digested biosolids. We also have temporal data from a single treatment plant in Tucson, Arizona dating
back to 1985.

Biosolids, land application, risks from human pathogens

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