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

Abstract

a b s t r a c tThe 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: RuO 2 /Ti anodic oxidation (AO), AO in the presence of electrogenerated H 2 O 2 (AO-H 2 O 2 ), AO-H 2 O 2 in the presence of UVA (AO-H 2 O 2 -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-H 2 O 2 -UVA process, about 36% of the TOC was removed after 6 h electrolysis, while 28% of the TOC was removed in the AO-H 2 O 2 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 hydroxylation 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 NH 4 + along with a very small proportion of NO 3 − 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.

Elucidation of the degradation pathways of sulfonamide antibiotics in a dielectric barrier discharge plasma system

“…Furthermore, it can be seen in Fig. 8(a) and (b) [40]. Besides, Gonçalves et al [19] reported that amine group and isoxazole ring in SMZ form NH 4 + and NO 3 À ions, respectively.…”

“…[28,29,39], and it has been well known that inorganic ions such as NO 3 À , NH 4 + and SO 4 2À are generated by cleavages of bonds containing N and S atoms during the oxidation treatment [19,40,41]. The toxicity of degradation byproducts may be a matter of concern.…”

“…To understand the degradation characteristics of the antibiotics, the changes of the LC-MS/MS chromatograms taken at 0, 1,2,5,10,15,20,25,30,35,40,45,50,55 and 60 min in full scan mode were examined. The sample taken at the time when the most various kinds of byproducts appeared was further analyzed by high-resolution LC-TOF-MS to identify their molecular structures.…”

Biodegradability enhancement of wastewater containing cefalexin by means of the electro-Fenton oxidation process

“…3 shows the effect of different ferrous ion concentrations ranging from 0 to 3.5 mM under EF conditions for the electrolysis of 200 mg/L of cefalexin with an applied current of 6.66 mA/cm 2 , and a pH of 3 for 480 min. The ferrous ion catalyzes the decomposition of H 2 O 2 into the reactive species ( • OH) that oxidize the CEX molecules [9,[32][33][34][35][36] After 8 h of treatment, the TOC removals were 8%, 22%, and 49% for 0, 0.5 and 1 mM of Fe 2+ concentrations, respectively. When the initial concentration of Fe 2+ ions in the solution raised from 0 to 1 mM, a remarkable enhancement in the TOC decay was observed.…”

Recent Overview of Solar Photocatalysis and Solar Photo-Fenton Processes for Wastewater Treatment

“…was also reported [61,77] (18)) [59]. It should be noted that the dimerization generally occurs at higher concentration of hydroxyl radicals, and such higher concentration is possible with the higher voltage (or current) applied [79].…”