Degradación fotocatalítica de xenobióticos en agua potable mediante procesos avanzados de oxidación (paos)

Abstract

PHOTOCATALYTIC DEGRADATION OF XENOBIOTIC COMPOUNDS IN DRINKING WATER BY ADVANCED OXIDATION PROCESSES (AOPS) Marina Martínez Menchón Department of Agricultural Chemistry, Geology and Pedology. University of Murcia. Spain. Ph. D. Dissertation to obtain the Doctor in Environmental Sciences Degree. ABSTRACT Water pollution can be defined as the action and effect of introducing matters or energy forms, or to induce conditions in the water that, in a direct or indirect way, imply a harmful alteration of its quality in connection with the later uses or with its ecological function. This makes that the availability of drinking water decreases and therefore, we have apply treatment methods, more or less expensive, to extract the residues and avoid indirect damages in the ecosystem, although it is not always possible. In this context, we propose the use of Advanced Oxidation Processes (AOPs), concretely photochemical (photo-Fenton and heterogeneous photocatalysis) processes under solar irradiation, for the elimination or at least reduction of the residue levels of certain xenobiotic compounds with different phisico-chemical characteristics and harmful effects on the Environment. These processes (AOPs), as method for the elimination of pollutants in water are based in the generation of hydroxyl radicals (highly oxidants) capable of quickly degrading organic substances to CO2, H2O and mineral salts. Thus, if this natural process is optimized and the reactions between a photocatalyst (Fe2+/Fe3+, or semiconductors like TiO2, ZnO or SnO2) and oxidants such as H2O2 o S2O82- are accelerated, the process is shown as an interesting and simple method to eliminate pollutants unlike other methods which are only able to move them from one place to another without getting their elimination. With this aim, in this work the photocatalytic degradation of eight pesticides, six polycyclic aromatic hydrocarbons and four trihalomethanes at pilot plant scale has been studied. For this purpose, ZnO and TiO2 (heterogeneous photocatalysis) and Fe2+ (homogeneous photocatalysis) have been use as photosensitizers. The obtained results show that the addition of photocatalysts, mainly ZnO and Fe2+, strongly enhances the degradation rate of pollutants.. In a general way, the pseudo first-order model (monophasic model) satisfactorily explained the degradation process for the different xenobiotic classes, although in some cases, the biphasic models better predict the results obtained. Finally, the economic evaluation of the solar detoxification treatment has been carried out. Keywords: Drinking water, pesticides, polycyclic aromatic hydrocarbons, trihalomethanes, solar photocatalysis.