Neutralization of Bacterial Aerosols by Aerodynamic Shocks in a Novel Impactor System: An Integrated Computational and Experimental Study

Neutralization of bacterial aerosol releases is critical in countering bioterrorism. As a possible bacterial aerosol neutralization method that avoids the use of chemicals, we investigate the mechanical instabilities of the bacterial cell envelope in air as the bacteria pass through aerodynamic shocks. To carry out this fundamental investigation, a novel experimental impactor system is designed and built to simultaneously create a controlled and measured shock and to collect the bacteria after they pass through the shock. In the impactor system, the aerosol flows through a converging nozzle, perpendicular to a collection surface that has an orifice through which the shocked bacteria enter a deceleration tube. Both experimental measurements of the pressure in the impactor system at multiple points and computational fluid dynamics simulations are used to characterize quantitatively the shocks created in the impactor. Specifically, the developed computational model describes the evolution of both the gas and particle velocity and temperature in the impactor system to determine the forces exerted on the bacterial aerosol as they pass through the shock. The results indicate that the developed computational model predictions compare well with the experimental pressure measurements.;The bacteria experience relative deceleration because of sharp velocity changes in the aerodynamic shock created in the experimental impactor system. Computational model results indicate that vegetative E. coli, cells require a critical acceleration of 3.0 x 108 m/s 2 compared to 3.9 -- 16 x 109 m/s 2 for B. atropheus spores to break-up. Computed accelerations in the impactor system reach 5.9 x 109 m/s2 which predict break-up of both vegetative cells and spores. Experimental findings demonstrate that aerosolized E. coli, cells and B. atropheus spores that pass through aerodynamic shocks created in the experimental impactor system are an order of magnitude less likely to retain viability than those that pass through the impactor at conditions which do not lead to the generation of an aerodynamic shock, and therefore, do not reach the critical acceleration required for break-up. However, B. atropheus spores that do not break-up have a higher likelihood to remain live compared to E. coli.