Background. The development of alternative processes to eliminate pathogenic agents in water is a matter of growing interest. Current drinking water disinfection procedures, such as chlorination and ozonation, can generate disinfection by-products with carcinogenic and mutagenic potential and are not readily applicable in isolated rural communities of less-favored countries. Solar disinfection processes are of particular interest to water treatment in sunny regions of the Earth. Solar light may be used to activate a photocatalyst or photosensitizer that generates, in the presence of molecular oxygen dissolved in water, reactive oxygen species (ROS), such as the radical, singlet oxygen , or superoxide , which are toxic to waterborne microorganisms. Method of Approach. Wild and collection-type Escherichia coli have been selected as model bacteria. Inactivation of such bacteria by either nanoparticles, water-soluble tris(-bipyridine)ruthenium(II) dichloride or Rose bengal (RB) subject to simulated sunlight have been compared. Although is the prototypical material for heterogeneous photocatalysis, the other two dyes are known to generate significant amounts of by photosensitization but have different chemical structures. The concentration of dye, illumination time, photostability, presence of scavengers, and post-treatment regrowth of bacteria have been investigated. Results. After of solar illumination the Ru(II) complex produced a strong loss of E. coli culturability monitored with solid selective agars. Both the collection- and wild-type bacteria are sensitive to the treatment with of dye. This photosensitizer showed a better inactivation effect than and the anionic organic dye RB due to a combination of visible light absorption, photostability, and production of and other ROS when bound to the bacterial membrane. A complete loss of culturability was observed when the initial concentration was , with no bacteria regrowth detected after of the water treatment. At higher initial microorganism levels, culturability still remains and regrowth is observed. Scavengers show that the radical is not involved in bacteria inactivation by photosensitization. Conclusions. A higher quantum yield of ROS generation by the sensitizing dyes compared to the semiconductor photocatalyst determines the faster sunlight-activated water disinfection of photodynamic processes. The homogeneous nature of the latter determines a more efficient interaction of the toxic intermediates with the target microorganisms. Solid supporting of the Ru(II) dye is expected to eliminate the potentials problems associated to the water-soluble dye.
A Comparison of Solar Photocatalytic Inactivation of Waterborne E. coli Using Tris (-bipyridine)ruthenium(II), Rose Bengal, and
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Rengifo-Herrera, J. A., Sanabria, J., Machuca, F., Dierolf, C. F., Pulgarin, C., and Orellana, G. (December 12, 2005). "A Comparison of Solar Photocatalytic Inactivation of Waterborne E. coli Using Tris (-bipyridine)ruthenium(II), Rose Bengal, and ." ASME. J. Sol. Energy Eng. February 2007; 129(1): 135–140. https://doi.org/10.1115/1.2391319
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