Effect of μM Fe addition, mild heat and solar UV on sulfate radical-mediated inactivation of bacteria, viruses, and micropollutant degradation in water

In this work, solar disinfection (SODIS) was enhanced by moderate addition of Fe and sodium perox- ydisulfate (PDS), under solar light. A systematic assessment of the activating factors was performed, firstly isolated, then in pairs and concluded in the combined Fe/heat/solar UV-PDS activation process. Solar light was the most effective (single) activator, and its combination with Fe and heat (double activation) yielded high level of synergies (up to S 1⁄4 2.13). The triple activation was able to reduce the bacterial load up to 6-log in less than 1 h, similarly to the photo-Fenton process done in comparison (SODIS alone: >5 h). Fe-oxides were suitable activators of PDS under the same conditions while the presence of organic matter enhanced bacterial inactivation by the triple activated PDS process. The degradation of a (selected) mixture of micropollutants (i.e. drugs, pesticides) was also achieved in similar order of magnitude, and faster than the photo-Fenton process. Finally, the removal of a viral pathogen indicator (MS2 bacteriophage) was attained at minute-range residence times. The aforementioned facts indicate the suitability of the mild, combined process, as a potential SODIS enhancement, producing safe drinking water for sunny and especially for developing countries.

Enhancing solar disinfection of water in PET bottles by optimized in-situ formation of iron oxide films. From heterogeneous to homogeneous action modes with H2O2 vs. O-2 - Part 2: Direct use of (natural) iron oxides

Stefanos Giannakis, César Pulgarin, Sami Rtimi, Sakine Shekoohiyan

Solar disinfection (SODIS) is a well-accepted intervention method, leading to an improvement in contaminated water sources. In this work, we attempted to further enhance the bacterial inactivation process during light exposure. By means of iron oxide addition, we generated a film on the inner surface of PET bottles used in SODIS, in order to induce further pathways of solar-mediated inactivation. More specifically, in this 2nd part, the deposition process has been systematically assessed, using iron oxides (Fe-Ox). The deposition parameters, namely, the precursor concentration (50 mg/L to 1 g/L), deposition time (1-4 h), oxide type (semiconductor, Fe species), size (mu m vs. nm), and specific surface area (similar to 5-150m(2)/g), were assessed. The use of H2O2 as the electron acceptor (and heterogeneous photo-Fenton induction) enhanced the efficacy without decreasing the reuse potential. More than 60% and 75% reduction in the treatment time was observed, compared with that for SODIS in a normal bottle, with O-2 and H2O2 (in situ photo-Fenton) as the electron acceptors, respectively. The semiconductor mode of action and controlled iron leaching in the system both demonstrated bactericidal capacity; particularly, it was found that the factors affecting the process partially correlated with the oxide characteristics (size, band gap, and isoelectric point), rather than the capacity to photo-dissolve iron. Consequently, the use of a natural Fe source yielded results (deposition parameters and efficacy) resembling those for iron salts, indicating the dominant inactivation pathways governing the process in the presence or absence of H2O2. Finally, the disinfection of natural lake water with natural Fe-deposed bottles showed similar results to those of Fe-salt-deposed bottles, indicating that in a suitable matrix, the process can work equally well.

ELSEVIER SCIENCE SA2019

Enhancing solar disinfection of water in PET bottles by optimized in-situ formation of iron oxide films. From heterogeneous to homogeneous action modes with H2O2 vs. O-2 - Part 1: Iron salts as oxide precursors

Stefanos Giannakis, César Pulgarin, Sami Rtimi, Sakine Shekoohiyan

Solar disinfection (SODIS) is a WHO-accepted intervention method for improving water sources in developing countries. Despite its effectiveness, the limitations of long exposure and bacterial regrowth risk demand further improvement of the practice. In this work, we have generated an iron oxide film on the inner surface of PET bottles used in SODIS, to generate further pathways of solar-mediated inactivation, namely a semiconductor mode of action and controlled iron leaching in the system, which both have demonstrated bactericidal capacity. More specifically, in this Part 1, the deposition process using Fe salts has been scrutinized, assessing the use of various homogeneous Fe precursors (FeCl3 , FeSO4 and Fe-2(SO4)(3)), amounts of iron (0.5-20 g/L) and deposition time (1-8 h) to find the delicate balance among deposition layer thickness and light penetration. At the optimal conditions (4 h deposition, 1 g/L FeCl3 ) SODIS was enhanced, reducing 60% the exposure time; a simple washing step brought a further reduction (70%), while eliminating regrowth in volumes from 330 up to 1500 mL reactors. A robust process and reactor was attained, able to reuse its precursor solution almost 10 times and the reactor in 5 consecutive tests, without the need for re-deposition. The modification also proved to be an invaluable iron source to fuel the photo-Fenton process, when H2O2 as an electron acceptor was added to the system. The improvement induced by the heterogeneous photo-Fenton process was around 80% compared to the SODIS/H2O2 process in plain PET bottles and exceeded 85% when compared to SODIS, while being durable to the high oxidative conditions. Finally, in the view of application in drinking water treatment, the process performed well in the lightly acidic region, due to the physicochemical implications of natural waters' pH in iron cycling.

ELSEVIER SCIENCE SA2019

Detrimental vs. beneficial influence of ions during solar (SODIS) and photo-Fenton disinfection of E. coli in water: (Bi)carbonate, chloride, nitrate and nitrite effects

Stefanos Giannakis, César Pulgarin

In this work, we studied the effect of inorganic ions occurring in natural waters on E. coli inactivation by solar and photo-Fenton processes, two crucial methods for drinking water treatment in sunny or developing countries. HCO3-, Cl-, SO42-, NO3-, NO2- and NH4+ were assessed at relevant concentrations for their inhibiting or facilitating role. The inactivation enhancement during solar disinfection (SODIS) was mainly attributed to the generation of HO center dot radicals produced during by excitation of NO3-, NO2-, while the HO center dot of photo-Fenton may be transformed into other radical species in presence of ions. Natural organic matter (NOM) was found to enhance both processes but also to hinder most of the enhancing ions, except for NO2-; modeling with the APEX software unveiled the inter-relations in the presence of NOM, and the possible inactivation activity by NO2 center dot. The photo-Fenton inactivation was more significantly enhanced by ions than SODIS (besides the case of NO3-, NO2-), but both processes were found robust enough.

2020

Stefanos Giannakis, César Pulgarin, Sami Rtimi, Sakine Shekoohiyan

ELSEVIER SCIENCE SA2019

Stefanos Giannakis, César Pulgarin, Sami Rtimi, Sakine Shekoohiyan

ELSEVIER SCIENCE SA2019