Solar photolytic ozonation for the removal of recalcitrant herbicides in river water

Photolytic ozonation of a river water has been performed by means of simulated solar radiation. The application of solar radiation, limiting the complete radiation spectrum (300-800 nm) to 320-800 nm and 390-800 nm, during the aqueous ozone decomposition has been assessed. A kinetic mechanism, including the influence of initiation, promotion and scavenging substances has been proposed, successfully modeling the experimental data. Radiation improves O-3 decomposition rate, as a promoter, being higher if the complete UV-visible spectrum is applied. Also, pH positively influences O-3 decomposition rate from pH = 4 to 8. Photolytic ozonation has been also proved to be effective in the removal of a mixture of three pyridine herbicides, dissolved in the river matrix. Radiation filters (320 nm and 390 inn cut-off) and pH have been selected as the main variables of the study. The enhanced oxidation rate registered when applying solar radiation and O-3 relays on the higher formation of hydroxyl radicals, responsible for the oxidation of these recalcitrant-toozone herbicides. Moreover, the estimated R-cr ratios confirmed the minimal differences of applying radiation or not at increasing pH, what is due to the ability of hydroxide anion to catalyze the decomposition of O-3 into HO center dot. The mineralization of the photolytic ozonation process (300-800 nm) reached 60%, whatever the pH considered. The increase of pH minimizes the differences in mineralization between the two technologies, the single ozonation achieving 50% at alkaline pH.