Inactivation of Bacillus subtilis spores using various combinations of ultraviolet treatment with addition of hydrogen peroxide.

This study aims at comparing the inactivation of Bacillus subtilis spores by various combinations of UV treatment and hydrogen peroxide (H2O2) addition. The combinations included sequential (UV-H2O2, H2O2-UV) and simultaneous (UV/H2O2) processes. Results showed that B. subtilis spores achieved a certain inactivation effect through UV treatment. However, hardly any inactivation effect by H2O2 alone was observed. H2O2 had a significant synergetic effect when combined with UV treatment, while high irradiance and H2O2 concentration both favored the reaction. When treated with 0.60 mm H2O2 and 113.0 μW/cm(2) UV irradiance for 6 min, the simultaneous UV/H2O2 treatment showed significantly improved disinfection effect (4.13 log) compared to that of UV-H2O2 (3.03 log) and H2O2-UV (2.88 log). The relationship between the inactivation effect and the exposure time followed a typical pseudo-first-order kinetics model. The pseudo-first-order rate constants were 0.478, 0.447 and 0.634 min(-1), for the UV-H2O2, H2O2-UV and UV/H2O2 processes, respectively, further confirming the optimal disinfection effect of the UV/H2O2 process. The disinfection could be ascribed to the OH radicals, as verified by the level of para-chlorobenzoic acid (pCBA).