Bioaerosol transport modeling and risk assessment in relation to biosolid placement

A field study was performed in which bioaerosols were sampled at a field si te undergoing land placement of anaerobically digested, de-watered biosolid material. The data from these field studies were then used to generate mic robial release rates from the biosolids for use in modeling bioaerosol tran sport. Continuous-point sources represented by large biosolid piles (tempor ary storage before placement) in the field, and continuous-area sources rep resented by Large fields upon which biosolids were placed by spraying, were modeled using microbial transport models; and downwind microbial concentra tions were generated. These quantified transport data were then entered int o microbial dose-response models in an attempt to characterize the risk of pathogenic bacteria and viruses infecting workers and nearby population cen ters. 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 rendi tions and 1 hr of exposure, The route of exposure proposed in this model is the transport, inhalation, deposition, and swallowing of bacterial or vira l pathogens. Note that these risk models by nature would tend to overestima te the actual risk to populations (wastewater workers) consisting primarily of immunocompetent individuals. Under these low-wind conditions, nearby po pulation centers where such immunocompetent populations may exist there con sidered to be 10 000 m from the (and 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.