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RESEARCH PAPERS

A Comparison of Solar Photocatalytic Inactivation of Waterborne E. coli Using Tris (2,2-bipyridine)ruthenium(II), Rose Bengal, and TiO2

[+] Author and Article Information
Julián A. Rengifo-Herrera

 Laboratory for Environmental Biotechnology, Ecole Polytechnique Fédèrale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

Janeth Sanabria, Fiderman Machuca, Carlos F. Dierolf

Grupo de Investigación en Procesos Avanzados de Oxidación para Tratamientos Químicos y Biológicos, Facultad de Ingeniería,  Universidad del Valle, A.A. 25360, Cali, Colombia

Cesar Pulgarin

 Laboratory for Environmental Biotechnology, Ecole Polytechnique Fédèrale de Lausanne (EPFL), CH-1015 Lausanne, Switzerlandcesar.pulgarin@epfl.ch

Guillermo Orellana

Laboratory of Applied Photochemistry, Department of Organic Chemistry, Faculty of Chemistry,  Complutense University of Madrid, 28040 Madrid, Spainorellana@quim.ucm.es

J. Sol. Energy Eng 129(1), 135-140 (Dec 12, 2005) (6 pages) doi:10.1115/1.2391319 History: Received July 27, 2005; Revised December 12, 2005

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 HO radical, singlet oxygen (O21), or superoxide (O2), 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 TiO2 nanoparticles, water-soluble tris(2,2-bipyridine)ruthenium(II) dichloride or Rose bengal (RB) subject to simulated sunlight have been compared. Although TiO2 is the prototypical material for heterogeneous photocatalysis, the other two dyes are known to generate significant amounts of O21 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 1hr 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 210mgL1 of dye. This photosensitizer showed a better inactivation effect than TiO2 and the anionic organic dye RB due to a combination of visible light absorption, photostability, and production of O21 and other ROS when bound to the bacterial membrane. A complete loss of culturability was observed when the initial concentration was 103CFUmL1, with no bacteria regrowth detected after 24hr of the water treatment. At higher initial microorganism levels, culturability still remains and regrowth is observed. Scavengers show that the HO 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.

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Figures

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Figure 1

Phototoxic effect of 2.0mgL−1Ru(bpy)3Cl2∙6H2O on ATCC E. coli (initial concentration: 105CFUmL−1): -◆- Ru(bpy)32++light, -◻- only light, -▵- Ru(bpy)32+ without light

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Figure 2

Comparison between photocatalytic and photodynamic disinfection processes, using 105CFUmL−1 ATCC E. coli, [Ru(bpy)3Cl2∙6H2O]=2mg∕L−1, [RB]=2mg∕L−1, [TiO2]=1g∕L−1, -◆- Ru(bpy)32+, -∎- Rose Bengal (RB), -▴- TiO2

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Figure 3

---- Spectral distribution of the xenon lamp used in the experiments and UV-Vis absorption spectra of --- Rose bengal and—Ru(bpy)32+ in water

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Figure 4

Evolution of the absorbance of Rose bengal (2mg∕L−1) and Ru(bpy)3Cl2∙6H2O(2mg∕L−1) in air-equilibrated aqueous solution on illumination at 550nm and 450nm, respectively: -◆- Rose Bengal (RB), -∎-Ru(bpy)32+.

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Figure 5

Effect of the Ru(bpy)32+ photosensitizer concentration and the addition of thiourea on E. coli ATCC (105CFUmL−1) inactivation by simulated sunlight: -◆-Ru(bpy)3Cl2∙6H2O2mg∕L−1; -∎-Ru(bpy)3Cl2∙6H2O10mg∕L−1; -▴- Ru(bpy)3Cl2∙6H2O10mg∕L−1+thiourea20mg∕L−1

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Figure 6

Evolution of the bacterial population at different initial levels after photoinactivation with 10mg∕L−1Ru(bpy)3Cl2∙6H2O or sunlight of (a) wild E. coli: -◆- Ru(bpy)32++light and E. coli4.0×105CFUmL−1, ◊ E. coli4.8×105CFUmL−1+light; -∎- Ru(bpy)32++light and E. coli4.0×103CFUmL−1; -◻- E. coli4.2×103CFUmL−1+light. (b) ATCC E. coli: -◆- Ru(phen)32++light and E. coli2.7×105CFUmL−1; ◇ E. coli4.1×105CFUmL−1+light; -∎- Ru(bpy)32++light and E. coli2.0×103CFUmL−1; -◻- E. coli1.7×103CFUmL−1+light

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Figure 7

Postirradiation events after 6h of sunlight illumination of waterborne (-◆-) ATCC 4.3×105CFUmL−1 or (-∎-) wild E. coli4.1×105CFUmL−1 in the presence of 10mg∕L−1Ru(bpy)3Cl2∙6H2O

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