Mineralization of antibiotic sulfamethoxazole by photoelectro-Fenton treatment using activated carbon fiber cathode and under UVA irradiation

摘要

The mineralization of antibiotic sulfamethoxazole (SMX) of concentrations up to 300 mg L~(-1) was examined by photoelectro-Fenton (PEF) using an activated carbon fiber (ACF) cathode with UVA (365 nm) irradiation. Comparative mineralization has been studied by different methods: RuO2/Ti anodic oxidation (AO), AO in the presence of electrogenerated H2O2 (AO-H2O2), AO-H2O2 in the presence of UVA (AO-H2O2-UVA), and both the electro-Fenton (EF) and PEF processes. PEF treatment at a low applied current of 0.36 A yields a faster and more complete depollution with 80% of the TOC removed after 6 h of electrolysis. The higher oxidative ability of the PEF process can be attributed to the additional hydroxyl radicals (~·OH) produced by the photo-Fenton reaction. The 63% mineralization in the case of EF treatment was due to the formation of short intermediates, such as carboxylic acids, which were difficult to oxidise with ~·OH. In the AO-H2O2-UVA process, about 36% of the TOC was removed after 6 h electrolysis, while 28% of the TOC was removed in the AO-H2O2 process. SMX is only slightly mineralized by the AO process, with only 25% of the TOC removed. HPLC-MS analysis allowed for up to six aromatic reaction products to be identified during the SMX degradation in the PEF process, mainly formed from the hydrox-ylation of the aromatic ring or/and isoxazole ring, accompanied by the substitution of the amine group (on aromatic cycle) or methyl group (on isoxazole ring) by ~·OH. The carboxylic acids generated, including oxalic, maleic, oxamic, formic and acetic acids, were detected by ion-exclusion chromatography. The initial organic nitrogen was mainly converted into NH4~+ along with a very small proportion of NO3~_ ion. Considering all the oxidation intermediates and end products for SMX degradation in the PEF process, a general mineralization mechanism by ~·OH and UVA was proposed.