Enhanced removal of methylisothiazolinone from high-salt wastewater by Sn-Sb-Ce/GAC particle electrode: Reactive species and efficiency

Advanced oxidation processes are promising for degradation of the highly chemical stability and refractory methylisothiazolinone (MIT) bactericides in relevant industrial wastewater. In order to assemble a low cost and high performance electrochemical oxidation system for wastewater treatment, granular active carbon (GAC) was decorated by doping Ce, Sn, Sb to synthesize Sn-Sb-Ce/GAC using sol-gel method as particle electrode filled into a three-dimensional (3D) electrochemical reactor. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) experiments revealed that the Sn-Sb-Ce/GAC particle electrode crystal particles were compact and uniform, and the surface structure was improved. The ten cyclic experiments indicated that the Sn-Sb-Ce/GAC particle electrode had high stability and low dissolution of the loaded active substance. The degradation mechanism of MIT was studied under the optimal working conditions of 3D electrode system with GAC of 5 g/L, current density of 20 mA/cm², initial pH 5, electrolyte concentration of Na₂SO₄ 0.02 mol/L and reaction time of 120 min. The indirect electrochemical degradation of MIT was dominated by active substance pathway that active chlorine rather than free radicals (^•OH) played the main role. Comparing with conventional two-dimensional (2D) electrode system, the 3D electrochemical system has larger active electrode area, higher treatment efficiency and lower energy consumption than the former. The 3D electrochemical system could remove 96.5 % of MIT from the actual high-salt reverse osmosis concentrate wastewater in 30 min. It has a certain removal effect on UV₂₅₄ in wastewater, but has a better removal effect on fluorescent substances. This study proposed a new strategy to develop transition metal and rare earth metal particle electrodes using carbon-based materials for high efficient electrocatalytic oxidation in the electrochemical treatment system.