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

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, mZVI(YF2) possessed the highest reactivity in H2O2 and the mZVI(YF2)/H2O2 system could remove 97.9% SMX at room temperature within 10 min. The degradation curve of SMX by mZVI/H2O2 at pH(ini) 3.0 could be divided into three phases: a lag phase, a rapid degradation phase, and a final stationary phase. Effects of pH(ini) 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 pH(ini). Increasing dosages of Fe-0 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 Fe and H2O2 also quickly decreased oxidative efficiency of SMX. Increasing dosages of SMX within the range of 5-100 mu M 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. (C) 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.