Bioaerosol transport modeling and risk assessment in relation to biosolid placement

A field study was performed in which bioaerosols were sampled at a field site undergoing land placement of anaerobically digested, de-watered biosolid material. The data from these field studies were then used to generate microbial release rates from the biosolids for use in modeling bioaerosol transport. Continuous-point sources represented by large biosolid piles (temporary storage before placement) in the field, and continuous-area sources represented by large fields upon which biosolids were placed by spraying, were modeled using microbial transport models; and downwind microbial concentrations were generated. These quantified transport data were then entered into microbial dose-response models in an attempt to characterize the risk of pathogenic bacteria and viruses infecting workers and nearby population centers. The risk of viral and bacterial infection to workers at biosolid land application sites is 3:100 and 2:100, respectively, under 2-m/s wind conditions and 1 hr of exposure. The route of exposure proposed in this model is the transport, inhalation, deposition, and swallowing of bacterial or viral pathogens. Note that these risk models by nature would tend to overestimate the actual risk to populations (wastewater workers) consisting primarily of immunocompetent individuals. Under these low-wind conditions, nearby population centers where such immunocompetent populations may exist (here considered to be 10 000 m from the land application sites) are predicted to be at little risk (1.95 x 10^-2:100) of infection from aerosolized bacteria and at no risk from aerosolized viruses.