Iron oxide-mediated semiconductor photocatalysis vs. heterogeneous photo-Fenton treatment of viruses in wastewater. Impact of the oxide particle size

The photo-Fenton process is recognized as a promising technique towards microorganism disinfection in wastewater, but its efficiency is hampered at near-neutral pH operating values. In this work, we overcome these obstacles by using the heterogeneous photo-Fenton process as the default disinfecting technique, targeting MS2 coliphage in wastewater. The use of low concentrations of iron oxides in wastewater without H2O2 (widstite, maghemite, magnetite) has demonstrated limited semiconductor-mediated MS2 inactivation. Changing the operational pH and the size of the oxide particles indicated that the isoelectric point of the iron oxides and the active surface area are crucial in the success of the process, and the possible underlying mechanisms are investigated. Furthermore, the addition of low amounts of Fe-oxides (1 mg L-1) and H2O2 in the system (1.5 and 10 mg L-1) greatly enhanced the inactivation process, leading to heterogeneous photo-Fenton processes on the surface of the magnetically separable oxides used. Additionally, photo-dissolution of iron in the bulk, lead to homogeneous photo-Fenton, further aided by the complexation by the dissolved organic matter in the solution. Finally, we assess the impact of the presence of the bacterial host and the difference caused by the different iron sources (salts, oxides) and the Fe-oxide size (normal, nano-sized). (C) 2017 Elsevier B.V. All rights reserved.

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

Iron oxides semiconductors are efficients for solar water disinfection: A comparison with photo-Fenton processes at neutral pH

Michaël Bensimon, Cristina del Socorro Lonfat, César Pulgarin, Andrzej Sienkiewicz

The photocatalytic activities of four different commercially available iron (hydr)oxides semiconductors, i.e. hematite (alpha-Fe2O3), goethite (alpha-FeOOH), wustite (FeO) and magnetite (Fe3O4), were evaluated for bacteria inactivation at neutral pH in the absence or presence of H2O2. Our results showed that heterogeneous photocatalysis and/or photo-Fenton processes catalyzed by low concentrations of reagents (0.6 mg/L Fe3+ and 10 mg/L H2O2) under sunlight may serve as a disinfection method for waterborne bacterial pathogens. In particular, we found that, with the exception of magnetite which need H2O2 as electron acceptor, all the other semiconductor iron (hydr)oxides were photoactive under sunlight in absence of H2O2 (using only oxygen as electron acceptor). Furthermore, for all iron (hydr)oxide studied in this work, no bacterial reactivation and/or growth was observed after photo-Fenton treatment. The same antimicrobial activity was obtained for the photocatalytic semiconducting action of hematite and goethite. Additionally, a delayed disinfection effect was observed to continue in the dark for the photo-assisted wilstite-based treatment. Electron spin resonance (ESR) in combination with spin-trapping was employed to detect reactive oxygen species (ROS) involved in heterogeneous photocatalysis and/or photo-Fenton treatments mediated by iron (hydr)oxide particles. In particular, ESR confirmed that center dot OH and O-2(center dot-) radicals were the principal ROS produced under photo-assisted action of iron (hydr)oxide particles in the absence or presence of H2O2. We also found that the components of natural water (i.e. natural organic matter (NOM) and inorganic substances) did not interfere with the photocatalytic semiconducting action of hematite to bacterial inactivation. However, these components enhance the bacterial inactivation by heterogeneous photo-Fenton action of hematite. Overall our results demonstrated, for the first time, that low concentration of iron (hydr)oxides, acting both as photocatalytic semiconductors or catalysts of the heterogeneous photo-Fenton process at neutral pH, may provide a useful strategy for efficient bacterial disinfection. (C) 2014 Elsevier B.V. All rights reserved.

Elsevier2015

Solar disinfection is an augmentable, in situ-generated photo-Fenton reaction Part 2: A review of the applications for drinking water and wastewater disinfection

Stefanos Giannakis, César Pulgarin

This is the second part of a comprehensive review article about photo-Fenton reaction at near-neutral pH used for water and wastewater disinfection. In this part, a critical revision of the fundamental physical, chemical and biological parameters affecting the photo-catalytic process efficiency are discussed. The effects of the chemical aspects, considered either as facilitators or competitors of photo-Fenton are deeply analyzed, with special focus on organic matter and its effect over bacterial inactivation. The role of solubilized iron and the biological nature of different pathogens are deeply assessed according to reported experimental data. Water temperature, turbidity, and radiation parameters like solar UV energy, ligh scattering and absorption during photo-Fenton are pictured in terms of treatment efficiency and suitable reactor design. Recent unconventional photo-Fenton strategies using iron chelates, iron oxides (including zero valent iron) and iron-based materials are also highlighted as new approaches to this process. Finally, the existing pilot scale studies in real conditions using photo-Fenton at near-neutral pH are revised, while alternative options and further research for real implementation are proposed. (C) 2016 Elsevier B.V. All rights reserved.

Elsevier2016

Stefanos Giannakis, César Pulgarin, Sami Rtimi, Sakine Shekoohiyan

ELSEVIER SCIENCE SA2019

Iron oxides semiconductors are efficients for solar water disinfection: A comparison with photo-Fenton processes at neutral pH

Michaël Bensimon, Cristina del Socorro Lonfat, César Pulgarin, Andrzej Sienkiewicz

Elsevier2015