Degradation of sodium dodecyl benzenesulfonate by vacuum ultraviolet irradiation

Abstract

Sodium dodecyl benzenesulfonate (SDBS) is a common anionic surfactant used in detergents, and a major household pollutant. SDBS released with bathing and laundry wastewater causes eutrophication of water bodies and toxicity in aquatic organisms. We compared the degradation of SDBS in aqueous solution, by vacuum ultraviolet (VUV, 254 nm and 185 nm) and ultraviolet irradiation (UV, 254 nm). Using lab-scale reactors, VUV degraded SDBS more efficiently than UV, also achieving a higher mineralization rate. HO was the main reactive oxygen species produced by VUV. SDBS concentration affected the distribution of absorbed VUV and UV photons, and influenced the reaction triggered. VUV was more efficient at lower concentrations, when indirect oxidation by HO was prevalent. The UV process, relied mostly on direct photolysis, and was affected slightly by initial concentration. VUV was more efficient at solution pH of 5 and 9, while UV performed better at alkaline conditions. Temperature increased the degradation rates for both processes. The addition of SO42− slightly promoted SDBS degradation in the VUV process, while Cl− and HCO3− inhibited it. For UV, SO42− and Cl− illustrated no significant difference on the degradation, while HCO3− had a positive impact on the system. We identified the four photoproducts of SDBS degradation by VUV, and proposed a degradation pathway. Finally, the fact the VUV could be efficiently used to remove anionic surfactant from real wastewater, proved that it can be applied efficiently with low energetic consumption.