Efficacy of Polarized Fibreglass Filters Irradiated by Ultraviolet Light in Capture and Inactivation of AerosolizedBacillus SubtilisSpores

Abstract

In this study, spores of Bacillus subtilis were used as a surrogate for spores of Bacillus anthracis. The mock-up air purification system consisted of one or two V-shaped banks of electrostatically polarized fibreglass filters that were installed within a rectangular wooden duct. Ultraviolet (UV) lights that swept across the surface of the filters were installed in front and back of the bank of filters. A nebulizer that contained a suspension of B. subtilis spores was placed in the duct in front of the filters. Air entering the duct passed through a high-efficiency particulate arresting (HEPA) filter and was drawn by a fan at the exit. Tests on up-stream and down-stream air collected with an Anderson air sampler showed that electrostatic polarization increased the efficiency of the filters in capturing spores by 51% or 38% at air speeds of 1.52 m/s or 2.54 m/s, respectively. Filter efficiency was also based on the number of spores that could be washed from the filters, and polarization increased this by as much as 92%. Challenge to the polarized filters with increasing levels of dust did not significantly reduce their efficacy in trapping spores (P>0.05) until the pressure drop across the filters exceeded 15 Pa. Ultraviolet irradiation for 5 minutes was sufficient to kill 73% of the spores on the front filters. The conclusion was that an air purification system consisting of polarized filters irradiated by UV light could be used to reduce spore contamination of the environment, including those of B. anthracis, and thereby reduce the risk of spreading disease.