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 (Fe-0) samples were investigated. The k(obs) value (pseudo-first-order rate constant) of SMX degradation by Fe-0/H2O2 or Fe-0/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 Fe(0 )corrosion in Fe-0/H2O2 and Fe-0/PS systems. Effects of WMF on SMX degradation kinetics by Fe-0/H2O2 or Fe-0/PS in the initial system pH (pH(ini)) range of 3.0-7.0 were studied. Although WMF accelerated SMX removal by Fe-0/H2O2 at pH(ini) 3.0 and 4.0, WMF did not exhibit advantages at higher pH(ini). In Fe-0/PS systems, WMF could promote SMX removal during the investigated pH range of 3.0-7.0, and k(obs) of SMX removal depended on the form of aquatic SMX which suggested that center dot SO4- could selectively degrade dissociated or protonated SMX. Although SO42-, Cl-, and NO3- showed different effects on SMX degradation by Fe-0/H2O2 or Fe-0/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 Fe-0/H2O2/WMF and Fe-0/PS/WMF systems were center dot OH and center dot SO4-, respectively. Meanwhile, the detection of ROS proved that WMF did not change the type of ROS in Fe-0/H2O2 or Fe-0/PS systems. Finally, degradation pathways of SMX by Fe-0/H2O2/WMF and Fe-0/PS/WMF were proposed based on transformation products.