Solar water disinfection | EPFL Graph Search

Solar water disinfection, in short SODIS, is a type of portable water purification that uses solar energy to make biologically-contaminated (e.g. bacteria, viruses, protozoa and worms) water safe to drink. Water contaminated with non-biological agents such as toxic chemicals or heavy metals require additional steps to make the water safe to drink. Solar water disinfection is usually accomplished using some mix of electricity generated by photovoltaics panels (solar PV), heat (solar thermal), and solar ultraviolet light collection. Solar disinfection using the effects of electricity generated by photovoltaics typically uses an electric current to deliver electrolytic processes which disinfect water, for example by generating oxidative free radicals which kill pathogens by damaging their chemical structure. A second approach uses stored solar electricity from a battery, and operates at night or at low light levels to power an ultraviolet lamp to perform secondary solar ultraviolet wat

Solar disinfection of viruses (SODIS): inactivation of coliphages MS2 and phiX174, human adenovirus and echovirus in water from Switzerland and India

Alex Dionisio Calado

Access to safe drinking water remains a challenge in many regions of the world. New methods to treat drinking water are constantly developped and improved in both in industrialised countries and in developing countries. SODIS is an interesting household-level disinfection technique that simply consists of pouring water into a PET bottle and exposing it to sunlight for at least 6 hours. Bacteria are efficiently inactivated by sunlight during SODIS, but the efficiency of SODIS on virus removal is much less studied. In this work, the inactivation of bacteriophages MS2 and phiX174, and human echovirus and adenovirus was studied in three different waters, two from India and one from Switzerland. Good removal (4 logs in 6 hours at 22°C and a fluence rate of 600 1.34 kJ/cm2) of MS2 was achieved in Swiss tap water, while less efficient inactivation was achieved in both Indian waters for MS2 and echovirus (1 log in 6 hours at 22°C and a fluence rate of 1.34 kJ/cm2). Both phiX174 and adenovirus were much more resistant to SODIS disinfection and less than 1 log of inactivation was obtained in Swiss tap water for phiX174. However, inactivation was not significantly different from the dark control in Indian water and for all experiments with adenovirus. Echovirus was inactivated similarly than MS2 and adenovirus was equally slow as phiX174. An increased temperature during SODIS enhanced inactivation substantially; 6 logs in 6 hours could be expected at 45 °C and with a fluence rate of 1.34 kJ/cm2. Indirect-solar inactivation was responsible for the MS2 removal, while direct inactivation via sunlight absorption of genome was not occurring during SODIS. We argue that iron could be responsible for the formation of reactive oxygen species which react with the viruses and yield their inactivation. The slower inactivation in Indian waters was probably due to the quenching effect of the higher concentration of organic matter. Removal of echoviruses during SODIS could be sufficient (4 logs in 6 hours) particularly at higher temperatures and for water with a low organic matter content. In contrast, SODIS may not be effective to remove Adenoviruses.

2013

Iron-oxides and iron-citrate as new photocatalysts in solar inactivation of Escherichia coli in water

Cristina del Socorro Lonfat

This study addresses the bacterial inactivation mechanism by photo-Fenton process at near-neutral pH, focusing on iron-oxides and iron-citrate as photocatalysts for solar water disinfection and using E. coli as a bacteria model. Cell envelope damage during bacterial inactivation by photo-Fenton and TiO2 photocatalysis were investing providing evidence for lipid peroxidation and cell permeability. TiO2 photocatalysis induced significant cell membrane damage, in contrast to the photo-Fenton process, but the inactivation kinetics for both disinfection processes was similar. A higher efficiency of photo-generation of reactive oxygen species (ROS) in the presence of TiO2 photocatalyst compared with the photo-Fenton system was observed. The bactericidal effect of Fe3+/hv seems possible due to the adsorption of Fe3+ ions on the bacterial cell wall followed by photosensitization of iron-bacteria exciplexes oxidizing the cell membrane. In contrast, the effect of Fe2+/hv was associated with diffusion into the cell giving raise to intracellular dark Fenton¿s reactions. We suggest that cell envelope damage might not necessarily be a unique pathway in bacterial inactivation by photo-Fenton treatment. In particular, the enhancement of an internal (photo)-Fenton process by the synergistic action of UVA and the external Fenton's reactants appears to be an important contribution to bacterial inactivation. Bacterial inactivation by the heterogeneous photo-Fenton process was carried out via iron (hydr)oxide particles, i.e. hematite, goethite, wüstite and magnetite. We found that, the iron (hydr)oxides act as photocatalytic semiconductors and catalysts in the heterogeneous photo-Fenton process with the exception of magnetite, which needs H2O2 as electron acceptors. The Hydroxyl radical and superoxide radical were the principal ROS produced by iron (hydr)oxide particles under light in the absence or presence of H2O2. Natural organic matter (NOM) and inorganic substances did not interfere with the photocatalytic semiconducting action of hematite during bacterial inactivation, but enhanced bacterial inactivation mediated by hematite used as the photo-Fenton reagent. Our results demonstrated, for the first time, that low concentration of iron (hydr)oxides (0.6 mg/L) under sunlight, acting both as semiconductors or catalysts of the heterogeneous photo-Fenton process, may serve as a disinfection method for waterborne bacterial pathogens. Bacterial inactivation by the homogeneous photo-Fenton process was carried out using Fe¿citrate complex as a source of iron. The efficiency of the homogeneous photo-Fenton process using Fe-citrate complex strongly improved bacterial inactivation as compared with the FeSO4 and goethite as sources of iron. The bacterial inactivation rate increased in the order of goethite < FeSO4 < Fe-citrate, which agreed with the ¿OH radicals detected by ESR. Encouraging results were also obtained while applying this treatment for bacterial inactivation in natural water samples at pH 8.5. No bacterial reactivation and/or growth were observed showing that Fe-citrate-based photo-Fenton process efficiently inactivate bacteria using a low iron concentration of Fe-citrate, while avoiding precipitation of ferric hydroxides. The application of the photo-Fenton process at near-neutral pH is a promising technique for bacterial inactivation, due to its simplicity, the use of the sun, the low concentration of reagents and does not produce toxic waste.

EPFL2015