Solar light (hv) and H2O2/hv photo-disinfection of natural alkaline water (pH 8.6) in a compound parabolic collector at different day periods in Sahelian region

The photo-disinfection of natural alkaline surface water (pH 8.6 +/- 0.3) for drinking purposes was carried out under solar radiation treatments. The enteric bacteria studied were the wild total coliforms/Escherichia coli (10(4) CFU/ml) and Salmonella spp. (10(4) CFU/ml) naturally present in the water. The photo-disinfection of a 25-l water sample was carried out in a solar compound parabolic collector (CPC) in the absence and in the presence of hydrogen peroxide (H2O2). The addition of H2O2 (10 mg/L) to the sample water was sufficient to enhance the photo-disinfection and ensure an irreversible lethal action on the wild enteric bacteria contents of the sample. The inactivation kinetic of the system was significantly enhanced compared to the one carried out without H2O2 addition. The effect of the solar radiation parameters on the efficiency of the photo-disinfection were assessed. The pH has increased during the treatment in all the photo-disinfection processes (hv and H2O2/hv). The Salmonella spp strain has shown the best effective inactivate time in alkaline water than the one recorded under acidic or near-neutral conditions. The evolution of some physico-chemical parameters of the water (turbidity, NO2 (-), NO3 (-), NH4 (+), HPO4 (2-), and bicarbonate (HCO3 (-))) was monitored during the treatment. Finally, the possible mechanistic process involved during the enteric bacteria inactivation was suggested

Mechanism of photocatalytic bacterial inactivation on TiO2 films involving cell-wall damage and lysis

This article addresses the cell wall damage of Escherichia coil (from now on E. coil) by TiO2 suspensions. The dynamics of TiO2 photocatalysis by thin films layers is described. The films were characterized by FTIR spectroscopy and atomic force microscopy (AFM). The E coil complete inactivation is shown to be due to the partial damage of the cell-wall components (peroxidation). A small increase in the cell wall disorder concomitant with a decrease of the cell wall functional groups leads to higher cell wall fluidity as the precursor step preceding cell lysis. (C) 2012 Elsevier B.V. All rights reserved

Polystyrene CuO/Cu2O uniform films inducing MB-degradation under sunlight

This study reports on a Cu-sputtered film on polystyrene (PS) leading to the discoloration/degradation of methylene blue (MB) under low intensity solar simulated irradiation. Direct current magnetron sputtering (DCMS) was used to graft uniform, adhesive Cu/Cu oxides on the polystyrene substrate. The kinetics of Cu-PS mediated MB-discoloration adding H2O2 was observed to take place within 90-120 min. The surface potential and pH variation was followed on the Cu-PS surface during MB-discoloration. Insight is provided for the observed changes relating them to the dye discoloration mechanism. The concentration, mean-free path and lifetime of the oxidative radical leading to MB-degradation were estimated. The Cu/Cu-oxides on the PS were characterized by X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) evidence for redox catalysis involving Cu(I)/Cu(II)-species was detected during MB-discoloration. Also by XPS the surface atomic percentage concentration was determined for the topmost Cu-PS layers. The Cu-PS coatings were also investigated for their optical and crystallographic properties. (C) 2016 Elsevier B.V. All rights reserved

Accelerated self-cleaning by Cu promoted semiconductor binary-oxides under low intensity sunlight irradiation

Uniform adhesive TiO2–ZrO2 films co-sputtered on polyester (PES) under low intensity sunlight irradiation discolored methylene blue (MB) within 120 min. The discoloration kinetics was seen to be accelerated by a factor four by TiO2–ZrO2–Cu containing ∼0.01% Cu, as determined by X-ray fluorescence (XRF). TiO2–ZrO2–Cu also increased also accelerated by a factor the discoloration of MB compared to TiO2/Cu(PES). MB discoloration was also monitored under visible light in the solar cavity by using a 400 nm cutoff filter. Photocatalyst surfaces were characterized by spectroscopic methods showing the film optical absorption and by X-ray photoelectron spectroscopy (XPS), the surface atomic percentage concentration up to 120 nm (∼600 layers). The band-gaps of TiO2–ZrO2 and TiO2–ZrO2–Cu were estimated for films co-sputtered for different times. By Fourier transform attenuated infrared spectroscopy (ATR-FTIR), the systematic shift of the predominating νs(CH2) vibration-rotational MB bands was monitored up to complete MB discoloration under low intensity solar simulated light. Evidence is presented for the OHradical dot generation by TiO2–ZrO2–Cu participating in the self-cleaning mechanism. The photo-induced interfacial charge transfer (IFCT) on the TiO2–ZrO2–Cu is discussed in terms of the electronic band positions of the binary oxides and Cu intra-gap states. This study presents the first evidence for a Cu-promoted composed of two binary oxide semiconductors accelerating the self-cleaning performance

Relevant impact of irradiance (vs. dose) and evolution of pH and mineral nitrogen compounds during natural water disinfection by photo-Fenton in a solar CPC reactor

The inactivation of total coliforms/E. coli (10(4) CFU/mL) and Salmonella spp. (10(5) CFU/mL) in well water naturally containing dissolved (Fe2+/3+) and solid iron forms (e.g. iron oxides) was carried out by photo Fenton treatment (Fe-2+,Fe-3+/H2O2/hv). In a preliminary run under simulated solar radiation, beyond 4 mg/L of added H2O2, the enteric bacteria were totally inactivated after 90 min. Thereafter, 25 L of well water were treated in the compound parabolic collector (CPC) under direct solar radiation. Three irradiation periods (i) 8 am to 2 pm (8-14h), (ii) 10 am to 4 pm (10-16 h) and (iii) 12 pm to 6 pm (12-18 h) were evaluated for assessing the impact of different solar irradiances (W m(-2)) on the enteric bacterial inactivation rates. Both studied strains were totally inactivated under sole exposure to solar radiation in the CPC when the experiments were conducted from 8 to 14h or 10 to 16 h. However, Salmonella spp. strains regrowth was noticed after the 24 h dark storage in all the samples previously treated with bare solar radiation. As the treated water contained Fe, the photo-Fenton disinfection at field scale in the CPC was carried out with the addition of H2O2 (10 mg/L). Significant enhancement of the enteric bacteria inactivation rate was therefore recorded comparatively to the one obtained under bare solar treatment. No regrowth was observed in water treated by photo-Fenton disinfection one week after the treatment. The comparative evaluation of photo-Fenton disinfection rate as a function of different irradiation periods was based on the monitoring of the effective disinfection time (EDT), or required time to acquire the total inactivation of targeted bacteria in defined conditions. Therefore, significant impact of the irradiance on the process was noticed. High average irradiance (Al) of 35W m(-2) led to the total inactivation of Salmonella spp. in an EDT of 45 min and a dose of 26 Wh m(-2); while low irradiance of 20W m(-2) required-an-EDT of 180 min for a-dose-60 Wh m(-2). Thus, the experiments revealed that lower irradiance level leads to higher doses to achieve the bacterial disinfection. pH, as well as nitrite and nitrate concentration, increased during the photo-disinfection processes, while depletion was recorded for aqueous ammonia concentration. (c) 2013 Published by Elsevier B.V

Innovative semi-transparent nanocomposite films presenting photo-switchable behavior and leading to a reduction of the risk of infection under sunlight

Novel sputtered polyethylene-TiO2 (PE-TiO2) thin films induce fast bacterial inactivation with concomitant photo-switchable hydrophobic to hydrophilic transition under light. RF-plasma pretreatments allowed an increased TiO2 loading on PE, favorably affecting the photocatalyst performance. ATR-FTIR spectroscopy shows that the increase in the cell lipid-layer fluidity leads to cell wall scission/bacterial inactivation

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

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

The bactericidal effect of TiO2 photocatalysis involves adsorption onto catalysts and loss of membrane integrity, FEMS

The bactericidal effect of photocatalysis with TiO2 is well recognized, although its mode of action is still poorly characterized. It may involve oxidation, as illuminated TiO2 generates reactive oxygen species. Here we analyze the bactericidal effect of illuminated TiO2 in NaCl–KCl or sodium phosphate solutions. We found that adsorption of bacteria on the catalyst occurred immediately in NaCl–KCl solution, whereas it was delayed in the sodium phosphate solution. We also show that the rate of adsorption of cells onto TiO2 is positively correlated with its bactericidal effect. Importantly, adsorption was consistently associated with a reduction or loss of bacterial membrane integrity, as revealed by flow cytometry. Our work suggests that adsorption of cells onto aggregated TiO2, followed by loss of membrane integrity, is key to the bactericidal effect of photocatalysis.GPAONational Licence