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

Effects of UV-LED Irradiation on E. coli in Water Disinfection

“…In photocatalytic disinfection, addition of TiO 2 (1.0 g/L) resulted an interesting finding. Whereas the inactivation efficiency was increased in both the 310 and 370 nm UV-LEDs by the addition of TiO 2 , that for the 267 and 275 nm UV-LEDs was drastically decreased [48]. Note that, anatase phase of TiO 2 that was used in our work has a bandgap of around 3.20 eV [52].…”

“…The photon energy from the 267, 275, 310 and 370 UV-LEDs was calculated and found to be 7:45 Â 10 À19 , 6:87 Â 10 À19 ,6:42 Â 10 À19 , and 5:11 Â 10 À19 J, respectively. This indicates that, UVA wavelength is the most appropriate in photocatalytic disinfection as was confirmed by a significant enhanced inactivation efficiency by the 370 nm UV-LED when anatase phase of TiO 2 was added in the E. coli suspension [48]. The enhanced inactivation efficiency by the 370 nm UV-LED with TiO 2 is therefore attributable to the huddle effect of the UV photons and OH • radicals.…”

“…Therefore, the 267 and 275 nm UV-LEDs required an average fluence of 12 and 15 mJ/cm 2 , respectively for the 4-log to be achieved in E. coli inactivation. Meanwhile the other UV-LEDs required a relatively higher fluence for the same 4-log inactivation to be achieved [48,49]. This finding indicated that UVC wavelengths have a higher germicidal effect in the inactivation of E. coli as also confirmed by their relatively higher average inactivation rate constant (k) of 0.4 and 0.3 for the 267 and 275 nm UV-LEDs, respectively compared to insignificant <0.03 for the 310 and 365 nm UV-LEDs.…”

“…As mentioned earlier in the introduction section, E. coli has the ability to undergo repair after damage from UV light irradiation. In all the experiments conducted, photo-repair was more dominant with an average of above 5% of photo-repair and negligible or no dark repair occurred [48,49], demonstrating that photo-effect is the dominant mechanism of E. coli repair. The dominance of photo-effect in E. coli repair was also reported in other studies in Refs.…”

“…This indicates that UV light is the key requirement in both photolytic and photocatalyic inactivation. In both the photolytic and photocatalytic experiments, lower wavelengths were found to have a higher inactivation efficiency than longer wavelengths (267 > 275 > 310 > 370 nm) [48]. Specifically, in photolytic inactivation, an average fluence of 5, 7, 800 and 900 mJ/cm 2 was required by the 267, 275, 310 and 370 nm UV-LEDs, respectively per order of log inactivation.…”