Bio-aerosol dispersal from Hog operations: Modeling and Measurement

The transfer of viable bacteria from individual hog operations to other nearby hog operations or human dwellings is a controversial issue in agriculture. A study to evaluate the atmospheric dispersion of viable bacteria from the exhaust fans of confined hog finishing buildings was conducted in Fall 1999. The downwind 'plume' of the fan emissions were sampled for total bacteria counts using single-stage Andersen viable particle samplers with blood and MacConkey agar plates. Additional size-fractionated aerosol collections were made within the buildings and at the exhaust fan using six-stage Andersen viable particle samplers. A total of 796 agar and 209 MacConkey plates were sampled on five days. Associated atmospheric conditions monitored during each sample day included air temperature, humidity, wind speed and direction, the three dimensional structure of turbulence, the one dimensional turbulent fluxes of heat and water vapor, and net radiation. Results showed elevated (above ambient) atmospheric concentrations of bacteria up to 100 to 600 m downwind of the buildings under near-neutral to unstable atmospheric conditions. The concentration of bacteria in the exhaust was about 150,000 cfu/m3. Viable bacteria can be transported at least 800 m under favorable conditions. The bacteria present however did not typically include human disease-causing species. While 25% of incubated MacConkey plates showed bacterial growth, only two plates (1%) tested positive for E. coli.. No colonies of Streptococcus suis or Salmonella were detected. The dispersion of the bio-aerosols in the near-field environment was modeled using both Lagrangian and Eulerian approaches. Turbulent statistics used in modeling the bacterial concentrations of the aerosol plume were derived from three-dimensional sonic anemometer measurements. The presentation will include an analysis of the two modeling approaches to modeling near-field aerosol dispersion.