Comparison of disinfection effects of UV light at 172, 222, 254 nm on Bacillus subtilis spores

The efficacy of ultraviolet (UV) disinfection at wavelengths of 172, 222 and 254 nm of Bacillus subtilis spores was evaluated. A Xe2* excilamp, a KrCl* excilamp and a low-pressure mercury lamp were used as the UV light sources at these three wavelengths, respectively. The first-order inactivation rate constants at 172, 222 and 254 nm were 0.0022, 0.122, 0.069 cm2 mJ-1, respectively, and, therefore, the 2 log reduction of B. subtilis spores required fluences of 909, 21.6, and 40.4 mJ cm-2 at the above respective wavelengths. This means that UV exposure at 172 nm is much less efficient than the exposures at the other two wavelengths for the inactivation of B. subtilis spores, while UV exposure at 222 nm is more efficient than that at 254 nm. The results suggest possible applications of Xe2* and KrCl* excilamps to microorganism disinfection.