Different Inactivation Behaviors of MS-2 Phage and Escherichia coli in TiO ₂ Photocatalytic Disinfection

Abstract

Despite a wealth of experimental evidence concerning the efficacy of the biocidal action associated with the TiO 2 photocatalytic reaction, our understanding of the photochemical mechanism of this particular biocidal action remains largely unclear. It is generally accepted that the hydroxyl radical (·OH), which is generated on the surface of UV-illuminated TiO 2 , plays the main role. However, our understanding of the exact mode of action of the hydroxyl radical in killing microorganisms is far from complete, and some studies report that other reactive oxygen species (ROS) (H 2 O 2 and O 2 · ؊ , etc.) also play significant roles. In particular, whether hydroxyl radicals remain bound to the surface or diffuse into the solution bulk is under active debate. In order to examine the exact mode of action of ROS in inactivating the microorganism, we tested and compared the levels of photocatalytic inactivation of MS-2 phage and Escherichia coli as representative species of viruses and bacteria, respectively. To compare photocatalytic microbial inactivation with the photocatalytic chemical degradation reaction, para-chlorobenzoic acid, which rapidly reacts with a hydroxyl radical with a diffusionlimited rate, was used as a probe compound. Two different hydroxyl radical scavengers, tert-butanol and methanol, and an activator of the bulk phase hydroxyl radical generation, Fe 2؉ , were used to investigate their effects on the photocatalytic mode of action of the hydroxyl radical in inactivating the microorganism. The results show that the biocidal modes of action of ROS are very different depending on the specific microorganism involved, although the reason for this is not clear. It seems that MS-2 phage is inactivated mainly by the free hydroxyl radical in the solution bulk but that E. coli is inactivated by both the free and the surface-bound hydroxyl radicals. E. coli might also be inactivated by other ROS, such as O 2 · ؊ and H 2 O 2 , according to the present results.

Titanium Oxide Antibacterial Surfaces in Biomedical Devices

“…Malondialdehyde (MDA) is released as a product of membrane degradation. It has been suggested that the free radicals •OH and H 2 O 2 were responsible for killing close to the TiO 2 , with H 2 O 2 acting at a distance (118,(148)(149)(150)(151)(152). Direct oxidation of bacterial components is feasible when cells are in direct contact with the surface of TiO 2 .…”

Optimizing Parameters on Nanophotocatalytic Degradation of Ibuprofen Using UVC/ZnO Processes by Response Surface Methodology

“…The following series of elementary reaction steps (Eqs. 1-8) are a simplified for reactions involving ZnO [10]: [11].…”

Synergistic Water-Treatment Reactors Using a TiO2-Modified Ti-Mesh Filter

“…Therefore, no matter what oxidant was produced by VUV photolysis, it would not be consumed by the purification process due to the long distance (several millimeters) [31]. On the other hand, Cho et al reported the difference of efficiency among waterborne pathogens by reactive oxygen species [32][33][34][35][36][37]. These studies indicate that bacteria could be inactivated by all forms of reactive oxygen species produced by photocatalysis, while viruses demonstrate notably higher resistance to photocatalytic inactivation.…”