Weak magnetic field for enhanced oxidation of sulfamethoxazole by Fe0/H2O2 and Fe0/persulfate: Performance, mechanisms, and degradation pathways

In this study, effects of the nonuniform weak magnetic field (WMF) on sulfamethoxazole (SMX) degradation rate by H2O2 and persulfate (PS) coupled with different zero-valent iron (Fe0) samples were investigated. The kobs value (pseudo-first-order rate constant) of SMX degradation by Fe0/H2O2 or Fe0/PS was accelerated by WMF irradiation. Meanwhile, the release rate of dissolved iron was increased in the presence of WMF which indicated WMF irradiation could promote Fe0 corrosion in Fe0/H2O2 and Fe0/PS systems. Effects of WMF on SMX degradation kinetics by Fe0/H2O2 or Fe0/PS in the initial system pH (pHini) range of 3.0-7.0 were studied. Although WMF accelerated SMX removal by Fe0/H2O2 at pHini 3.0 and 4.0, WMF did not exhibit advantages at higher pHini. In Fe0/PS systems, WMF could promote SMX removal during the investigated pH range of 3.0-7.0, and kobs of SMX removal depended on the form of aquatic SMX which suggested that SO4− could selectively degrade dissociated or protonated SMX. Although SO42−, Cl−, and NO3− showed different effects on SMX degradation by Fe0/H2O2 or Fe0/PS, WMF could accelerate SMX degradation in the presence of these common anions. Chemical quenching experiments and electron paramagnetic resonance (EPR) studies identified that main reactive oxygen species (ROS) generated in Fe0/H2O2/WMF and Fe0/PS/WMF systems were OH and SO4−, respectively. Meanwhile, the detection of ROS proved that WMF did not change the type of ROS in Fe0/H2O2 or Fe0/PS systems. Finally, degradation pathways of SMX by Fe0/H2O2/WMF and Fe0/PS/WMF were proposed based on transformation products.