Comparison of UV-LED photolytic and UV-LED/TiO2 photocatalytic disinfection for Escherichia coli in water

Ultraviolet (UV) light irradiation is the latest disinfection method and TiO2 is a well-known photocatalyst to generate reactive oxygen species. With the newly emerging UV-LEDs, however, the study of UV-LED/TiO2 photocatalytic disinfection is still rear. In this work, by using Escherichia coli (E. coli) as a model microbe, UV-LED photolytic and UV-LED/TiO2 photocatalytic disinfections were conducted under diverse conditions to examine their inactivation efficiency, repression potential on the repair of bacteria after UV inactivation and the electrical energy consumption. The results showed that increasing the irradiance enhanced the inactivation of E. coli in both photolysis and photocatalysis, especially the former. For a given irradiance of 0.49 mW/cm(2) from the 365 nm UV-LEDs, 1.0 g/L was found to be the optimal TiO2 concentration. Then, the dependence of disinfection on wavelengths (265, 275, 310 and 365 nm) was studied at an irradiance of 0.49 mW/cm(2) with 1.0 g/L TiO2. The highest inactivation efficiency was achieved by the 265 nm followed by the 275 nm UV-LEDs in both photolytic and photocatalytic disinfection. For these two wavelengths, the addition of 1.0 g/L TiO2 can significantly repress the E. coli repair, whereas the inactivation efficiency becomes slightly worse. On the other hand, when irradiated by wavelengths of 310 and 365 nm, both inactivation efficiency and suppression of repair were significantly improved. Either with TiO2 or not, the irradiation by 275 nm exhibited higher inactivation efficiency. Taking into full consideration of inactivation efficiency, suppression of repair and power consumption, the 275 nm UV-LED/TiO2 was suggested to be a promising option for water disinfection.