Study of photocatalytic damages induced on E. coli by different photocatalytic supports (various types and TiO2 configurations)

Photocatalysis, based on UV irradiation of a TiO2 support to generate oxygen free radicals, has been shown to have antibacterial properties, but the process has yet to be optimized. Photocatalytic inactivation of Gram negative bacteria, E. coli, was studied on five different photocatalytic supports, in terms of TiO2 type (Degussa P25/Millennium PC500) and configurations (catalyst was impregnated on supports, alone or with binder, or suspended in water). Several irradiation times were tested. Effective UV-A doses were estimated using a simulation based on a Monte Carlo approach to facilitate comparison between supports. For the same TiO2 type, inactivation efficiency was best with the “suspension” configuration (up to 4 log in 120 min) followed by the “impregnated without binder” configuration (up to 2 log in 120 min) and finally the configuration with binder (only 0.5 log after 120 min). In the “suspension” configuration, TiO2 P25 appeared to be more effective than TiO2 PC500. This may be due to smaller dispersed particle sizes. Our experiments highlight the importance of optimizing contact between the bacteria to be inactivated and titanium dioxide particles. Bacterial regrowth was compared on two culture media with different nutrients, and revealed metabolic damage induced by photocatalysis. Based on the classical Chick–Watson model, the kinetics of the photocatalytic process were determined, including a lag time for several supports.