Electrolytic and electro-irradiated processes with diamond anodes for the oxidation of persistent pollutants and disinfection of urban treated wastewater.

This paper analyzes the advantages and drawbacks of the combination of UV irradiation with electrolysis with the aim to give insight about the feasibility of the application of this technology for the reclaiming of conventionally-treated wastewater. The oxidation of synthetic solutions containing five selected model complex pollutants has been compared, showing that UV irradiation improves the results of electrolysis for progesterone, metoprolol and caffeine and deteriorates the performance for the degradation of sulfamethoxazole and dimethyl-phthalate. Differences observed becomes lower when mineralization is compared showing that the effects of UV irradiation are diluted when a mixture of species is oxidized. Results suggest that high ThOD/TOC (Theoretical Oxygen Demand/Total Organic Carbon) ratios improve the synergistic coupling of technologies while low values lead to a clear antagonistic effect. Because during oxidation progress this ratio is decreased, the observed effect on mineralization is much lower than in the oxidation of the raw molecule. Opposite to this low effect on the oxidation of organics, the improvement in the performance of the disinfection by coupling UV to electrolysis is much clearer. In addition, UV irradiation modifies significantly the chlorine speciation and helps to prevent the formation of hazardous species such as chlorate and perchlorate during the electrochemical processes.