Individual and simultaneous degradation of the antibiotics sulfamethoxazole and trimethoprim in aqueous solutions by Fenton, Fenton-like and photo-Fenton processes using solar and UV radiations

Abstract

The aim of this study was to compare the effectiveness of advanced oxidation processes (AOPs) based on Fenton and Fenton-like reagents with Solar and UV radiation (UV, UV/H2O2, Solar, Solar/H2O2, UV/H2O2/Fe2+, UV/H2O2/Fe3+, Solar/H2O2/Fe2+ and Solar/H2O2/Fe3+) for the single and simultaneous degradation of the antibiotics sulfamethoxazole (SMX) and trimethoprim (TMP) in aqueous solution. For direct photolysis processes, the degradation rate of SMX was highly enhanced, whereas that of TMP was slightly reduced, when the solution pH was increased from 3 to 12. The different photolytic behavior of SMX and TMP was investigated by DFT calculations, estimating in both cases the relative energies of the ground singlet state, the first excited singlet state, and the first triplet state. SMX triplet state is about 7.5 Kcal mol−1 above the TMP triplet state, which could justify the higher photodegradation obtained for SMX. The removal percentages of both antibiotics in the photo-Fenton and photo-Fenton-like systems were much greater than those in the conventional Fenton processes. Additionally, in both photo-Fenton processes, the degradation rates of SMX and TMP were faster by applying UV radiation than solar radiation. Complete mineralization of SMX was achieved in UV/H2O2 process; however, the Solar/H2O2/Fe3+ system yielded a maximum extent of mineralization of 42% for TMP. SMX and TMP photodegradation by-products were identified in UV, UV/H2O2, Solar, and Solar/H2O2/Fe3+ systems. The removal percentages and rates of degradation of SMX and TMP were influenced by the water matrix. It was shown that the Solar/H2O2/Fe3+ system yielded the highest removal percentage of TMP in surface water and of SMX in ground water. A high degree of SMX and TMP mineralization was obtained with both UV/H2O2 and Solar/H2O2/Fe3+systems, but the by-products were 50% less toxic with the latter system. The removal percentage and reaction rate for the single antibiotic degradation were reduced when both antibiotics were degraded simultaneously, attributable to the competition of SMX and TMP for the hydroxyl radicals generated when both pollutants are present.