Photocatalytic degradation of sulfamethoxazole in aqueous suspension of TiO2

The presence of drugs in the aquatic media has emerged in the last decade as a new environmental risk. The aim of this study is the evaluation of photocatalysis as a suitable process to degrade an antibiotic, the sulfamethoxazole. In this way, sulfamethoxazole in aqueous solution was treated by using titania in suspension as catalyst, and UV light. Sulfamethoxazole degradation and TOC reduction were improved when titania concentration was increased, until an optimum located between 0.5–1.0 g TiO2/L. Under the studied conditions, 82% of sulfamethoxazole degradation and 23% of TOC reduction was achieved when working with 0.5 g TiO2/L. The initial pH also seemed to influence the process in some extent, although the antibiotic degradation was not affected by this variable, TOC reduction was dramatically decreased when the initial pH was 2, probably due to interferences caused by the sulfate anion. The LC/MS study has been also carried out, and a mechanism has been proposed, through the identification of five intermediates. Sulfate and ammonium ions were also monitored in the solution finding that, as long as the sulfamethoxazole is degraded, the total amount of releasable ions was not reached. The SUVA parameter along the reaction shows a decrease on the aromatic content, but there is still a notable presence of the aromatic compounds after 15 h of reaction. Finally, the experimental data were fitted to different kinetic models. The best results were obtained for a model including the sulfamethoxazole and intermediates concentration.