Development and experimental validation of a thermal inactivation model for airborne bacteria and its application in Trombe wall systems

Abstract

Thermal inactivation technology is an effective and safe method to control indoor bioaerosols. A predictive mathematical model describing the effect of residence time and exposure temperature on the thermal inactivation process of Klebsiella pneumoniae (K. pneumoniae), Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) in aerosol was developed. A continuous flow experimental system was set up to determine the survival ratio of bioaerosols under the wall temperature of 45–120 °C and residence time of 1.5–12 s. The experimental results showed that the thermal stability in the order from high to low was S. aureus > K. pneumoniae > E. coli. The inactivation model was developed based on the first-order kinetic model and Arrhenius equation and the model parameters were identified through particle swarm optimization (PSO) algorithm with the input of time-dependent exposure temperature calculated by computational fluid dynamics (CFD). The survival ratio calculated by the present model corresponded well with that observed in the experiment, with root mean square error (RMSE) being 0.0445, 0.0433 and 0.0376 for K. pneumoniae, E. coli and S. aureus, respectively. Based on the heat and mass transfer model for Trombe wall, it was found that solar-driven thermal inactivation could reduce the indoor bacterial concentration by up to 57 % for E. coli with thermal efficiency being 0.424 under solar irradiance of 496 W/m² and ambient temperature of 12.8 °C. In this way, solar driven thermal inactivation is a promising and sustainable method to deal with indoor bioaerosols.