Use of coaxial photocatalytic reactor (CAPHORE) in the TiO2 photo-assisted treatment of mixed E-coli and Bacillus sp and bacterial community present in wastewater

This paper reports the photocatalytic disinfection of water contaminated by a mixture of Escherichia coli and Bacillus sp. as well as that of wastewater containing a larger microbial community. The photocatalytic reactions were carried out in a coaxial photocatalytic reactor called CAPHORE, using TiO2 P-25 of Degussa. E. coli is more sensitive than Bacillus sp. to photocatalytic treatment. Bacterial inactivation was dependent on organic matter and dissolved oxygen (DO) concentration. Of the bacterial community present in partially treated wastewater, E. coli appears to be more sensitive to the treatment than Enterococcus sp., coliforms (other than E. coli), and Gram-negative (other than coliforms). After photocatalytic treatment, no bacterial recovery of previous groups was observed for 24 It in the dark. However a very low bacterial inactivation rate was observed for the whole bacterial population present in wastewater and detected by non-selective media. The effective disinfection time (EDT), the time necessary for total inactivation of bacteria without re-growth in a subsequent dark period referenced at 24 h (or 48 h), was reached only for Enterococcus sp., and coliform groups. EDT24 was not reached for the whole Population. © 2005 Elsevier B.V. All rights reserved.

Bactericidal action of illuminated TiO2 on pure Escherichia coli and natural bacterial consortia: post-irradiation events in the dark and assessment of the effective disinfection time

César Pulgarin

Bactericidal action of illuminated TiO2 on pure culture of Escherichia coli K 12 and bacterial consortium was studied. Photocatalytic E. coli inactivation rate was dependent on the biological parameters such as: physiological state, generation and initial concentration of bacteria. The behavior of the bacterial suspension during the subsequent dark period was discussed in order to estimate the potential of using the photocatalytic treatment process in a real water disinfection Situation. The effective disinfection time (EDT) was defined as the time required for total inactivation of bacteria without re-growth in a subsequent dark period referenced at 48 It. An increase of E. coli concentration was observed after illumination of bacteria without TiO2 (named here as photolysis). In the presence of TiO2 (photocatalysis), the decrease of bacteria continues in the dark, and no regrowth was observed within the following 60 h. The extent) applied during the illumination period. Thus, of this "residual disinfecting effect" was dependent on the light intensity (400 or 1000 W/m(2)) EDT was reached in photocatalytic but not in photolytic treatment. Bacterial consortia present in two different wastewaters were phototreated with and without TiO2 and a significant difference in bacterial sensitivity to both phototreatments was observed. Enterococcus sp. appear to be less sensitive than coliforms and other Gram-negative bacteria. Considerable differences in photoreactivity were observed for both samples taken at the same place but at different date. The first sample named as wastewater 1, exhibited a bacteriostatic but no bactericidal effect after both phototreatments; the addition of TiO2 accelerated the solar disinfection. In the second sample, wastewater 2, a bactericidal effect was observed in photolytic and photocatalytic experiments and the EDT was attained in both cases, even if the bacterial inactivation rate was the lowest in the presence of the catalyst. The chemical oxygen demand (COD) decreases during photocatalytic treatment, but not during the photolytic one; whereas the Dissolved organic carbon (DOC) increases in both cases. COD/DOC ratio decreases during phototreatrnents. (C) 2003 Elsevier B.V. All rights reserved.

2004

Comparative effect of simulated solar light, UV, UV/H202 and photo-Fenton treatment (UV Vis/H2O2/Fe-2+,Fe-3+) in the Escherichia colt inactivation in artificial seawater

César Pulgarin

Innovative disinfection technologies are being studied for seawater, seeking a viable alternative to chlorination. This study proposes the use of H2O2/UV254 and photo-Fenton as disinfection treatment in seawater. The irradiations were carried out using a sunlight simulator (Suntest) and a cylindrical UV reactor. The efficiency of the treatment was compared for Milli-Q water, Leman Lake water and artificial seawater. The presence of bicarbonates and organic matter was investigated in order to evaluate possible effects on the photo-Fenton disinfection treatment. The photo-Fenton treatment, employing 1 mg L-1 Fe2+ and 10 mg L-1 of H2O2, led to the fastest bacterial inactivation kinetics. Using H2O2/UV254 high disinfection rates were obtained similar to those obtained with photo-Fenton under UV254 light. In Milli-Q water, the rate of inactivation for Escherichia coli was higher than in Leman Lake water and seawater due to the lack of inorganic ions affecting negatively bacteria inactivation. The presence of bicarbonate showed scavenging of the OH center dot radicals generated in the treatment of photo-Fenton and H2O2/UV254. Despite the negative effect of inorganic ions, especially HCOi, the disinfection treatments with AOPs in lake water and seawater improved significantly the disinfection compared to light alone (simulated sunlight and UV254). In the treatment of photo-Fenton with simulated sunlight, dissolved organic matter had a beneficial effect by increasing the rate of inactivation. This is associated with the formation of Fe3 -organo photosensitive complexes leading to the formation of ROS able to inactivate bacteria. This effect was not observed in the photoFenton with UV254 . Growth of E. coli surviving in seawater was observed 24 and 48 h after treatment with UV light. However, growth of surviving bacteria was not detected after photo-Fenton with UV254 and H2O2/UV254 treatments. This study suggests H2O2/UV254 and photo-Fenton treatments for the disinfection of seawater, in spite its high concentration of salts. (C) 2013 Elsevier Ltd. All rights reserved.

Elsevier2013

Fe vs. TiO2 Photo-assisted Processes for Enhancing the Solar Inactivation of Bacteria in Water

César Pulgarin

Batch solar water disinfection (SODIS) is a known, simple and low-cost water treatment technology. SODIS is based on the synergistic action of temperature increase and light-assisted generation of Reactive Oxygen Species (ROS) on bacteria. ROS are generated via the action of solar photons on i) Natural Organic Matter (NOM), ii) some mineral components of water (Fe oxides or Fe-organic complexes, nitrogen compounds) and iii) endogenous bacteria photosensitizers (e.g. cytochrome). SODIS has proven its effectiveness for remote settlements or urban slums in regions with high incident solar radiation. All of the internal and external simultaneous processes are often driven by photoactive Fe-species present in the cell, as well as in the natural water sources. In SODIS, a temperature of 50 degrees C is required and due to this temperature dependence, only 1-2 L can be treated at a time. As required exposure time strongly depends on irradiation intensity and temperature, some SODIS households could be overburdened, leading to inadequate treatment and probable bacterial re-growth. This is why TiO2 photocatalysis and Fe photo-assisted systems (i.e. photo-Fenton reactants) have been considered to enhance the photo-catalytic processes already present in natural water sources when exposed to solar light. Both TiO2 and Fe-photoassisted processes, when applied to water disinfection aim to improve the performance of solar bacteria inactivation systems by i) enhancing ROS production, ii) making the process independent from the rise in temperature and as a consequence iii) allowing the treatment of larger volumes than 1-2 L of water and iv) prevent bacterial (re)growth, sometimes observed after sole solar treatment.

Schweizerische Chemische Gesellschaft2015

Bactericidal action of illuminated TiO2 on pure Escherichia coli and natural bacterial consortia: post-irradiation events in the dark and assessment of the effective disinfection time

César Pulgarin

2004

Comparative effect of simulated solar light, UV, UV/H202 and photo-Fenton treatment (UV Vis/H2O2/Fe-2+,Fe-3+) in the Escherichia colt inactivation in artificial seawater

César Pulgarin

Elsevier2013