Degradation of methylene blue by an E-Fenton process coupled with peroxymonosulfate via free radical and non-radical oxidation pathways

Abstract

Advanced oxidation processes are often applied to a variety of refractory wastewater, but rarely is the electro-Fenton process combined with the activated persulfate process applied to printing and dyeing wastewaters. In this study, we have delicately designed a new advanced oxidation process for the degradation of persistent pollutants in wastewater. The zero-valent iron (ZVI) activated peroxymonosulfate process coupled with an electro-Fenton (EF-PMS) oxidation process is applied to treat methylene blue (MB) wastewater. Its main advantage is to generate more reactive oxygen species (ROS) and reduce the cost of oxidants. Experimentally, it was found that the degradation rate of the MB by the EF-PMS process was significantly higher than that before the coupling, and the mineralization rate can reach 56.84% within 2 h. According to free radical scavenging experiments and electron spin resonance (ESR) spectroscopy, the main ROS in the EF-PMS process were identified as ˙OH, SO₄˙⁻ and ¹O₂, where free radical oxidation played an important role in the removal of MB, accounting for 70.39% of the total removal efficiency. The mechanism of ROS generation and action in the EF-PMS process was investigated, and the pathway of MB degradation was determined by the identification of intermediates. The EF-PMS process was also effective in degrading MB in different water quality backgrounds as well as for process reuse. The removal efficiency of other organic compounds was also evaluated. The results indicate that the EF-PMS process has good potential for application.