Kinetic Modelling of Aromaticity and Colour Changes during the Degradation of Sulfamethoxazole Using Photo-Fenton Technology

Sulfamethoxazole (SMX) is an antibiotic that is extensively used in veterinary medicine, and its occurrence in wastewater and surface water can reach up to 20 μg/L. SMX is categorized as a pollutant of emerging concern by the US EPA due to its persistence and effects on humans and the environment. In this study, photo-Fenton technology is proposed for the removal of SMX. Aqueous solutions of SMX (50.0 mg/L) are treated in a 150 W UV photoreactor, using [Fe2+]0 = 0.5 mg/L and varying [H2O2]0 = 0–3.0 mM. During the reaction, colour (AU) was assessed along with SMX (mg/L), turbidity (NTU), and TC (mg/L). SMX degrades to aromatic intermediates with chromophoric groups, exhibiting colour (yellow to brown) and turbidity. As these intermediates are mineralized into CO2 and H2O, the colour and turbidity of the water lose intensity. Using a molar ratio of 1 mol SMX:10 mol H2O2, the maximum degradation of aromatic species takes place (71% elimination), and colourless water with turbidity < 1 NTU is obtained. A kinetic modelling for aromaticity loss and colour formation as a function of the oxidant concentration has been proposed. The application of this model allows the estimation of oxidant amounts for an efficient removal of SMX under environmentally friendly conditions.