Degradation of sulfamethoxazole (SMX) by water falling film DBD Plasma/Persulfate: Reactive species identification and their role in SMX degradation

The performance and mechanism of persulfate on improving the degradation of sulfamethoxazole (SMX) in a water falling film dielectric barrier discharge (DBD) plasma reactor have been studied. Both peroxymonosulfate (PMS) and peroxydisulfate (PDS) improved the degradation and mineralization of SMX, but PMS presented higher SMX degradation than PDS. Moreover, increases in applied voltage, solution pH and PMS/PDS concentration promoted SMX degradation. The reactive species were qualitatively and quantitatively detected by electron paramagnetic resonance (EPR) spectra and chemical probes. The results show that the activation process of PMS/PDS by discharge plasma produced reactive radicals including ·OH and SO4·-, and PMS led to higher aqueous O3 and ·OH concentrations than PDS; scavengers of ·OH, SO4·-, O2·- and 1O2 in SMX solution decreased SMX degradation, but scavengers of hydrated electrons and H· in SMX solution had little effect on SMX degradation. The detected degradation products of SMX included 5-amino-3-methylisoxazole, 4-aminobenzenesulfonic acid, nitrosobenzene and 4-nitro sulfamethoxazole, etc., and the calculation results show that most of these products had lower toxicities than SMX. Our study indicates that the combination of DBD plasma and PMS/PDS is an efficient pretreatment method for bio-treatment of refractory SMX.