Novel multistage fixed-bed photoreactor for bacterial inactivation using N-doped TiO2 nanoparticles under vis-LEDs and sunlight illumination

Abstract

In the selection and design of appropriate types of photoreactor system configuration in terms of total irradiated surface area of catalyst per unit volume in photocatalysis reaction, reaction kinetics and light distribution within the reactor are the most important factors. Though several photoreactor system configurations have been reported so far, most of them were complex, focused on degradation of hazardous organic compounds and their application has been very limited for pathogenic microorganism inactivation applications. In the present work, however, photocatalytic bacterial inactivation is studied by immobilized N-doped TiO2 using a novel simplified multistage fixed-bed photoreactor. The photoreactor has been developed from N-doped TiO2 nanoparticles immobilized on glass beads using tetraethoxysilicate (TEOS) as a binder with low-temperature synthesis route. The reactor was irradiated under visible light-emitting diodes (vis-LEDs) with the incident photon flux of 5.23 ± 0.35 × 1016 photons/s. Furthermore, for solar experiment global and UV irradiances were 71.2 and 4.6 mWcm−2, respectively. The photocatalytic inactivation efficiency was investigated on different types of Gram-negative and Gram-positive bacteria in water. From the photocatalytic inactivation efficiencies, the proposed photoreactor demonstrated more than 3 log unit reduction in bacterial removal on both under vis-LEDs and sunlight irradiation. Fast inactivation efficiency for all selected bacterial strain was also observed under sunlight irradiation when compared to under vis-LED irradiation. It has been understood that the rate of photocatalytic inactivation on Gram-negative bacteria was found to be higher than the Gram-positive bacteria on both experiments.