Photocatalytic inactivation of particle-associated Escherichia coli using UV/TiO2

We investigated the photocatalytic inactivation of free Escherichia coli and E. coli attached to carbon particles using granulated activated carbon filter effluent as a water sample. The inactivation rates of both free and attached E. coli exposed to UV/TiO2 were higher than that using UV irradiation alone. However, attached E. coli was barely inactivated because of the protection of particles, which acted as hotspots for protection against inactivation of attached E. coli in the effluent. During inactivation, a lower UV irradiation intensity favored inactivation by UV/TiO2 for a given UV irradiation dose (irradiation intensity over time), because a longer irradiation period favored higher disinfection efficiency. Particles with a diameter >8 mu m were predominantly responsible for protecting attached E. coli, and a higher particle concentration was associated with lower inactivation. The reactivation of E. coli after UV/TiO2 disinfection was lower than that after UV irradiation alone, and the reactivation rate decreased with increasing UV irradiation dose.