Degradation of sulfamethoxazole by a heterogeneous Fenton-like system with microscale zero-valent iron: Kinetics, effect factors, and pathways

Abstract

Abstract Five commercial microscale zero-valent iron (mZVI) samples showed different reactivity in sulfamethoxazole (SMX) removal in the presence of H2O2, which was independent of respective iron surface area but was consistent with the dissolved iron releasing rate. Of five mZVI samples, mZVIYF2 possessed the highest reactivity in H2O2 and the mZVIYF2/H2O2 system could remove 97.9% SMX at room temperature within 10 min. The degradation curve of SMX by mZVI/H2O2 at pHini 3.0 could be divided into three phases: a lag phase, a rapid degradation phase, and a final stationary phase. Effects of pHini, mZVI loading, SMX concentration, and H2O2 concentration on SMX degradation by mZVI/H2O2 were analyzed. Removal rates of SMX by mZVI/H2O2 dropped sharply upon increasing pHini. Increasing dosages of Fe0 ranged from 25 to 75 mg/L and H2O2 at low concentrations (below 0.5 mM) both enhanced SMX degradation, but a higher concentration of Fe0 and H2O2 also quickly decreased oxidative efficiency of SMX. Increasing dosages of SMX within the range of 5–100 µM progressively decreased the oxidation rates of SMX by mZVI/H2O2. Furthermore, three degradation pathways of SMX by mZVI/H2O2 process were proposed based on the combination of theoretical calculations and intermediates identification.