Inactivation by solar photo-Fenton in pet bottles of wild enteric bacteria of natural well water: Absence of re-growth after one week of subsequent storage

Iron photo-assisted inactivation of wild enteric bacteria (total coliforms/E. coil and Salmonella spp.) was carried out in water from the Sahelian wells having different pH (W1:4.9 and W2: 6.3) and a natural iron content of 0.07 mg/L We evaluate the efficiency of the disinfection on different systems containing both or only one Fenton reagent (H2O2/Fe-2.): (i) H2O2/Fe2+/hv, (ii) Fe2+/hv, (iii) H2O2/hv, and (iv) only light irradiation (hv) at lab and field scale. Generally, 0.6 mg/L of Fe2+ and/or 8.5 mg/L of H2O2 were used in the Fenton reagent. The systems H2O2/Fe2+/hv and H2O2/hv led to total inactivation of Salmonella and E. coil. The natural iron content (0.07 mg/L) was enough to drive an efficient photo-Fenton process leading to total bacterial inactivation. Our results show that: (i) the iron salt present in Sahelian water is enough to perform a photo-Fenton disinfection of drinking water when adding H2O2, (ii) addition of external iron salts at near neutral pH has no additional effect on the bacterial photo-Fenton inactivation process. After one week of storage, no enteric bacteria re-growth was observed in treated waters. Mechanistic suggestions are presented to explain the observed results. (C) 2012 Elsevier B.V. All rights reserved.

Evaluation of the efficiency of the photo Fenton disinfection of natural drinking water source during the rainy season in the Sahelian region

Juliette Ndounla, César Pulgarin

The photo-disinfection of water from two different wells (W1, pH: 4.6–5.1 ± 0.02) and (W2 pH: 5.6–5.7 ± 0.02) was carried out during the rainy season at Ouagadougou–Burkina Faso, West Africa. The weather variation during the rainy season significantly affects the photo-disinfection processes (solar disinfection and photo-Fenton). The dilution of the water by rainwater highly affected the chemical composition of the wells' water used in this study; very low iron contents Compared to the ones recorded during the dry season were recorded in all water samples. Both photo-disinfection processes were used to treat 25 L of water in a compound parabolic collector (CPC). None of them have shown the total inactivation of both wild enteric bacteria strains (total coliforms/E. coli and Salmonella spp.) involved in the treatment. However, the total coliforms/E. coli strains were totally inactivated during the exposure under most of the photo-Fenton treatment. Also, the remaining strains, especially those of Salmonella spp. were achieved during the subsequent 24 h of dark storage under the action of the Fenton process. Under uniquely solar radiation, total inactivation was recorded only in the total coliforms/E. coli strains. The impact of the available irradiance on the efficiency of the photo-Fenton disinfection of natural water was highlighted during the exposure under high intermittent solar radiation. The impact of the HCO3− concentration of both wells' water on the evolution of the pH during the photo-disinfection was recorded. Drastic decrease was noticed after the initial fast increase in presence of low HCO3− concentration while a steady state was observed after the increase in presence of higher concentration. The redox activities of the nitrogen components of the water during both photo-disinfection processes have led to increased concentration of nitrite in all the cases and variations were noticed in that of nitrate and ammonia.

Elsevier2014

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

Juliette Ndounla, César Pulgarin

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.

Elsevier2014

Dramatic enhancement of solar disinfection (SODIS) of wild Salmonella sp in PET bottles by H2O2 addition on natural water of Burkina Faso containing dissolved iron

César Pulgarin, Julian Andrés Rengifo Herrera, Frédéric Sciacca

Disinfection of surface water containing dissolved iron (0.3 mg L-1) at natural neutral pH (similar to 7.5) was carried out via solar disinfection (SODIS) treatment in PET bottles with H2O2 (10 mg L-1). Wild coliforms and Salmonella sp. were monitored for 6 h of sunlight irradiation and 72 h of dark post-treatment period. In our conditions, SODIS treatment Could not avoid Salmonella sp. re-growth during dark storage, meanwhile the addition of 10 mg L-1 of H2O2 showed a strong enhancement of the inactivation rate without any re-growth of both bacteria. Finally, total coliforms (Escherichia coli included) demonstrated to be an inappropriate indicator for monitoring bacterial contamination in water during solar disinfection processes. (C) 2009 Elsevier Ltd. All rights reserved.

2010

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

Juliette Ndounla, César Pulgarin

Elsevier2014

Evaluation of the efficiency of the photo Fenton disinfection of natural drinking water source during the rainy season in the Sahelian region

Juliette Ndounla, César Pulgarin

Elsevier2014