Efficient removal of endosulfan from aqueous solution by UV-C/peroxides: A comparative study

Highlights: • Removal of endosulfan was studied by UV-C and UV-based advanced oxidation processes (AOPs). • Among UV/S2O82−, UV/HSO5−, and UV/H2O2, endosulfan was removed the most efficiently by UV/S2O82−. • Hydroxyl and/or sulfate radicals were involved in the destruction of endosulfan and its by-products. • Presence of natural organic matter or alcohol inhibited the removal of endosulfan and its by-products. • Degradation pathways were proposed based on the nature of endosulfan degradation intermediates. -- Abstract: This study explored the efficiency of UV-C-based advanced oxidation processes (AOPs), i.e., UV/S2O82−, UV/HSO5−, and UV/H2O2 for the degradation of endosulfan, an organochlorine insecticide and an emerging water pollutant. A significant removal, 91%, 86%, and 64%, of endosulfan, at an initial concentration of 2.45 μM and UV fluence of 480 mJ/cm2, was achieved by UV/S2O82−, UV/HSO5−, and UV/H2O2 processes, respectively, at a [peroxide]0/[endosulfan]0 molar ratio of 20. The efficiency of these processes was, however, inhibited in the presence of radical scavengers, such as alcohols (e.g., tertiary butyl alcohol and isopropyl alcohol) and natural organic matter (NOM). The inhibition was also influenced by common inorganic anions in the order of nitrite > bicarbonate > chloride > nitrate ≃ sulfate. The observed pseudo-first-order rate constant decreased while the degradation rate increased with increasing initial concentration of the target contaminant. The degradation mechanism of endosulfan by the AOPs was evaluated revealing the main by-product as endosulfan ether. Results of this study suggest that UV-C-based AOPs are potential methods for the removal of pesticides, such as endosulfan and its by-products, from contaminated water