In this investigation, an experimental facility was developed for quantifying the inactivation of viable bioaerosol particles in a controlled axially heated air flow. The tests were conducted with Bacillus subtilis var. niger endospores. The thermal inactivation of aerosolized spores was measured based on the loss of their culturability that resulted from a short-term exposure to air temperatures ranging from 150 to >1000°C. The cross-sectional and longitudinal temperature profiles in the test chamber were determined for different heating and flow conditions. The characteristic exposure temperature (Te) was defined using a conservative approach to assessing the spore inactivation. Experimentally determined inactivation factors (IF) were corrected to account for the temperature profiles in the axially heated air flow. The reported IF-values serve as the lower approximation of the actual inactivation. Two data sets obtained at different flow rates, Q=18 and 36Lmin-1, represent different exposure conditions. In both cases, the thermal exposure of aerosolized spores produced no effect or only a moderate inactivation when the Te remained below 200°C for 18Lmin-1 and 250oC for 36Lmin-1. The IF-values increased exponentially by about four orders of magnitude as the temperature rose by 150°C. Depending on the flow rate, IF exceeded 104 at Te>320°C (Q=18Lmin-1) or >360°C (Q=36Lmin-1). At Te≈375-400°C, the spore inactivation obtained at both flow rates reached the limit of quantification established in this study protocol, which translates to approximately 99.999% viability loss. The findings were attributed primarily to the heat-induced damage of DNA and denaturation of essential proteins. Up to a certain level of the thermal exposure, these damages are repairable; however, the self-repair capability diminishes as the heat rises and then the damage becomes totally irreversible. The data generated in this study provide an important reference point for thermal inactivation of stress-resistant spores in various biodefense/counterterrorism and air quality control applications.
All Science Journal Classification (ASJC) codes
- Environmental Engineering
- Mechanical Engineering
- Fluid Flow and Transfer Processes
- Atmospheric Science
- Air flow
- High temperature