Enhancement of solar inactivation of Escherichia coli by titanium dioxide photocatalytic oxidation

Abstract

Aims: To improve solar water disinfection using a photocatalysing semi-conductor and to study the mechanisms involved in this process. Methods and Results: Cells of Escherichia coli were used as the microbiological indicator to study the possibility of improving the efficiency of solar water disinfection using titanium dioxide (TiO 2 ) as a photooxidizing semi-conductor. TiO 2 was used either as a suspended powder or in an immobilized form. Both applications improved the efficiency of solar disinfection. TiO 2 in suspension was more effective than the immobilized form, producing enhancement factors of 1AE62 and 1AE34, respectively. The concentration of TiO 2 greatly affected efficiency, with a maximum effect at 1 mg ml )1 . Higher TiO 2 concentrations reduced the efficiency. Dimethyl sulphoxide (DMSO) and cysteamine (Cys), hydroxyl radical (OH AE ) scavengers, were used to elucidate the mechanisms involved in the presence of TiO 2 . Both DMSO and Cys totally abolished the enhancing effect produced by the presence of TiO 2 . Conclusions: Sunlight has a potential water disinfecting capacity. The use of TiO 2 greatly improved this efficiency. The effect of TiO 2 was mainly concentration-dependent, giving maximum efficiency at 1 mg ml )1 . The presence of DMSO and Cys removed the TiO 2 -induced enhancement, indicating that OH AE may be involved in the process of cell killing.Significance and Impact of the Study: The efficiency of solar disinfection is limited and time-consuming and needs to be improved. The use of a semi-conductor is promising as it reduces the time of exposure and therefore increases the efficiency of solar disinfection. This would allow for the availability of good quality water, and hence would improve the quality of life.

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 .…”

Speeding up solar disinfection (SODIS): effects of hydrogen peroxide, temperature, pH, and copper plus ascorbate on the photoinactivation of E. coli

“…Sunlight exposure combined with water temperatures of 45-508C resulted in rapid, synergistic inactivation, (Wegelin et al 1994;Sommer et al 1997;McGuigan et al 1998) leading to the use of reflectors (Kehoe et al 2001;Rijal & Fujioka 2003;Mani et al 2006), bottles with the bottoms painted black (Sommer et al 1997), and thermoregulated reactors (Sommer et al 1997) to accelerate the process. Several groups have used TiO 2 as a suspended catalyst or coated onto a support to accelerate the photoinactivation of bacteria, (Ireland et al 1993;Dunlop et al 2002;Salih 2002;Rincon & Pulgarin 2004, 2006 while others have proposed the use of photosensitizers such as methylene blue in SODIS (Acher & Juven 1977;Wegelin et al 1994). These modifications have proven effective and promising, but still pose problems.…”

Additional Effects of Silver Nanoparticles on Bactericidal Efficiency Depend on Calcination Temperature and Dip-Coating Speed

“…The antibacterial effects of TiO 2 , either in suspension or immobilized, have been studied with respect to substrate support (e.g., glass and stainless steel) (2,12,25,37), the Ag/TiO 2 molar ratio (37), and the light source and wavelength (13,17,21,27). However, bactericidal effects are also affected by the condition of the glass coating, the photocatalyst ratio, and the sterilization process.…”