Degradation of Sulfamethoxazole by Electrochemically Activated Persulfate Using Iron Anode

Abstract In this study, sulfamethoxazole (SMX) was removed by electrochemically activated persulfate using iron anode. Different oxidation processes (persulfate alone, Fe2+/persulfate, electrolysis alone, electrochemically/Persulfate) were investigated, the results showed SMX could be more efficiently degraded under the electrochemically/Persulfate system. Central composite design (CCD) based Response surface methodology (RSM) was used to optimize and elucidate the individual and interactive effects of independent variables on the degradation kinetics of sulfamethoxazole. The maximum kinetics was predicted by CCD as pH 3.6, 18 mA applied current and 3.55 mM/L persulfate concentration. The results of free-radical scavenging experiments and electron paramagnetic resonance (EPR) indicated that both {\text{SO}}_4^{ \cdot - } and HO· were responsible for the degradation of SMX. The inhibition of methanol (MeOH) was lower than tertiary butanol (TBA), due to the generation of methanol radical (·CH2OH), which promoted the reduction of Fe3+to Fe2+. LC-ESI-TOF-MS analysis was done on SMX and its intermediates. The SMX degradation pathway during the electrochemical treatment was proposed. In addition, two typical inorganic anions ( {\text{C}}{{\text{l}}^ - },{\text{HCO}}_3^ -) were investigated and the inhibitory effect of {\text{HC}}O_3^ - was more obvious.