[Synergistic Disinfection Effects of Dual-wavelength Ultraviolet and Its Impact on Photoreactivation and Dark Repair]

Ultraviolet-C （UV-C） irradiation can effectively deactivate pathogenic microorganisms. The far UV-C （200-230 nm） and conventional UV-C （250-280 nm） can damage the proteins and nucleic acids of pathogenic microorganisms, respectively. The combination of far and conventional UV-C has the potential of synergistic inactivation. However, relevant studies remain limited owing to the lack of appropriate experimental setups. Therefore, this study established a mini-fluidic photoreaction system equipped with a KrCl excimer lamp and a low-pressure mercury lamp. This system could independently/simultaneously deliver stable 222 nm （far UV-C） and 254 nm （conventional UV-C） irradiations. Subsequently, the system was used to investigate the synergistic effect of dual-wavelength UV-C （the combination of 222 nm and 254 nm UV-C） on Escherichia coli （E. coli） inactivation and the subsequent impact on photo- and dark-reactivation. The results indicated that dual-wavelength UV-C had a significant synergistic effect on E. coli inactivation, with a synergistic coefficient up to 2.2. Additionally, comparing to 254 nm UV irradiation, the photo-reactivation of E. coli after dual-wavelength UV-C irradiation was weakened, with the maximum lg reactivation percentage reducing from 50.8% to 36.1%. Furthermore, E. coli after dual-wavelength UV-C irradiation exhibited dark decay, in which the inactivation efficiency was further enhanced during dark treatment. Therefore, these results suggest that dual-wavelength UV-C could inhibit the light reactivation and dark repair of E. coli, ensuring the water biosafety, as well as providing reference for the development of effective and safe water disinfection technologies.