pH-dependent transformation products and residual toxicity evaluation of sulfamethoxazole degradation through non-radical oxygen species involved process

Abstract The elimination of sulfamethoxazole (SMX) from water matrix is still challenging in advanced oxidation processes (AOPs) due to the hindrance by background constituents and the generation of toxic by-products, especially halogenated ones in the presence of halide ions. Herein we reported the catalytic degradation of SMX by combined reactive oxygen species (ROS), including both radical and non-radical mediated processes. The combined ROS of sulfate radicals (SO4•-), hydroxyl radicals and singlet oxygen (1O2) were generated from CuCo@MgxAlyOz hydrotalcite catalysts (named as CuCo-HT) and peroxymonosulfate (PMS). Removal of 97.6% on 0.10 mM SMX was achieved in 40 min with 65.4% stoichiometric efficiency of PMS, which was significantly higher comparing with classic sulfate radical mediated processes, and the activation energy of SMX removal was only 13.4 kJ mol-1. Water parameters such as initial pH, common anions and humic acid showed negligible influences on SMX removal. Noticeably the generation of BrO3- was completely inhibited in the presence of Br- in this radical/non-radical combined process. Moreover, the contribution of various ROS and the degradation pathway varied intensively under different pH. Along with the increase of pH, the mineralization of SMX was promoted, and the residual toxicity was better eliminated. Among the aforementioned ROS, SO4•- was disclosed as the most reactive oxidative species for the degradation of SMX. In addition, 1O2 favored mineralization of it. The outcomes demonstrated our approach of applying radical/non-radical combined systems to remove SMX was highly efficient for the elimination of toxicity of sulfonamide antibiotic contaminants under complex environmental conditions.