Examinando por Autor "Sordo, Carlos"

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Analogies and differences between photocatalytic oxidation of chemicals and photocatalytic inactivation of microorganisms
(ELSEVIER, 2010) Marugán, Javier; van Grieken, Rafael; Pablos, Cristina; Sordo, Carlos
This study reports the analogies and differences found when comparing TiO2 photocatalytic treatment for chemical oxidation and microorganisms inactivation, using methylene blue and Escherichia coli as references, respectively. In both processes the activation is based on the same physicochemical phenomena and consequently a good correlation between them is observed when analyzing the effect of operational variables such as catalyst concentration or incident radiation flux, both factors influencing common stages such radiation absorption and generation of reactive oxygen species. However, different microbiological aspects (osmotic stress, repairing mechanism, regrowth, bacterial adhesion to the titania surface, etc) makes disinfection kinetics significantly more complex than the first-order profiles usually observed for the oxidation of chemical pollutants. Moreover, bacterial inactivation reactions are found to be extremely sensitive to the composition of water and modifications of the catalysts in comparison with the decolorization of the dye solutions, showing opposite behaviors to the presence of chlorides, incorporation of silver to the catalysts or the use of different types of immobilized TiO2 systems. Therefore, the activity observed for the photocatalytic oxidation of organics can not be always extrapolated to photocatalytic disinfection processes.
Comparison of the photocatalytic disinfection of E.COLI suspensions in slurry, wall and fixed-bed reactors
(ELSEVIER, 2009) van Grieken, Rafael; Marugan, Javier; Sordo, Carlos; Pablos, Cristina
The performances of different configurations of photoreactors were compared for the photocatalytic disinfection of E. coli aqueous suspensions and methylene blue photodegradation. Titania was immobilized in an annular reactor in two different ways: on the inner reactor wall and on the packing of a fixed bed. The influence of the increase in the TiO2 layer thickness has been studied, and the results have been compared with those obtained with TiO2 slurries of increasing concentration. Experimental results for methylene blue degradation were in agreement with those expected from the characterization data of the immobilized systems, but they did not fit with the variation of the activity for microorganisms inactivation. The increase in the density of the TiO2 film caused by the heat treatment carried out after every coating cycle reduce the TiO2 surface available for the interaction with bacteria, although it remains accessible for the dye molecules. Although immobilized systems show a lower disinfection activity in deionized water than TiO2 slurries, they show a lower inhibition by the presence of organic matter, leading to comparable irradiation times to reach bacterial concentrations below the detection limit in the treatment of wastewater treatment plant effluents. Moreover, immobilized systems have shown that they are stable and do not present deactivation after several cycles of reuse, being readily applicable for continuous water treatment systems.
Kinetics of the photocatalytic disinfection of Escherichia coli suspensions
(ELSEVIER, 2009) Marugan, Javier; van Grieken, Rafael; Sordo, Carlos; Cruz, Cristina
The photocatalytic inactivation of E. coli suspensions has been successfully modelled with kinetic equations based on a simplified reaction mechanism using three parameters: kinetic constant (k), pseudo-adsorption constant (K) and inhibition coefficient (n). This model has been used to fit complex bacterial inactivation curves with shoulder and tails regions in addition to the classical log-linear behaviour. Experiments performed with increasing concentrations of titania, using TiO2/SiO2 photocatalysts and waters with different composition indicates that the most sensitive parameters are the kinetic and the pseudo-adsorption constant, whereas the values of the inhibition coefficient do not seem to be influenced by the experimental conditions in the range studied. The chemical composition of the water strongly influences the efficiency of the disinfection process. However, the effect of different inorganic anions has been found to be produced at very different concentration levels and by different mechanisms, which also affects the values of the kinetic and pseudo-adsorption constants in different ways. Similarly, low concentrations of humic substances inhibit the disinfection process whereas the same concentration of sucrose does not affect at all. Consequently, the macroscopic analysis of real waters based on conductivity and total organic carbon measurements must be carefully considered, as differences in the nature of the inorganic and organic substances present in similar waters could lead to unexpected results.
Photocatalytic inactivation of bacteria in water using suspended and immobilized silver TiO2
(ELSEVIER, 2009) van Grieken, Rafael; Marugan, Javier; Sordo, Carlos; Martinez, Patricia; Pablos, Cristina
Incorporation of silver to titanium dioxide is of great interest for photocatalytic disinfection applications since in addition to the enhancement of the electron-hole separation and interfacial charge transfer and the increase in the visible light response, silver compounds present a strong bactericidal effect. Ag/TiO2 materials used in suspension and immobilized in two different configurations (catalytic wall and fixed-bed reactors) have been prepared, characterized and tested using Escherichia coli as model microorganism. Although the incorporation of silver to powdered Degussa P25 TiO2 increases the activity, the thermal treatment required for the stabilization of the supported metal particles reduces the global efficiency. The comparison with experiments of dye photodegradation indicates that the activity of Ag/TiO2 is mainly due to the bactericidal role of silver and not to the enhancement of the photocatalytic mechanism. The best tested system has been proved to be the Ag/TiO2 catalytic wall reactor with a 0.6 wt% of Ag loading, showing a high activity both in relative (per gram of TiO2) and absolute terms, an optimal use of the radiation source, and a good stability of the film with negligible silver lixiviation, allowing the continuous treatment of water.