Efficient cephalexin degradation using active chlorine produced on ruthenium and iridium oxide anodes: Role of bath composition, analysis of degradation pathways and degradation extent

• Published in: The Science of the total environment Vol. 648; pp. 377 - 387
• Main Authors: Perea, Lic A., Palma-Goyes, Ricardo E., Vazquez-Arenas, Jorge, Romero-Ibarra, Issis, Ostos, Carlos, Torres-Palma, Ricardo A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.01.2019
• Subjects: Active chlorine; Electrochemical oxidation; RuO2-IrO2; Urine effluent; Wastewater treatment; β-Lactam; Active chlorine; RuO2-IrO2; β-Lactam; Urine effluent; Wastewater treatment; Electrochemical oxidation; RuO-IrO
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2018.08.148

The elimination of cephalexin (CPX) using electro-generated Cl2-active on Ti/RuO2-IrO2 anode was assessed in different effluents: deionized water (DW), municipal wastewater (MWW) and urine. Single Ti/RuO2 and Ti/IrO2 catalysts were prepared to compare their morphologies and electrochemical behavior against the binary DSA. XRD and profile refinement suggest that Ti/RuO2-IrO2 forms a solid solution, where RuO2 and IrO2 growths are oriented by the TiO2 substrate through substitution of Ir by Ru atoms within its rutile-type structure. SEM reveals mud-cracked structures with flat areas for all catalysts, while EDS analysis indicates atomic ratios in the range of the oxide stoichiometries in the nominal concentrations used during synthesis. A considerably higher CPX degradation is achieved in the presence of NaCl than in Na2SO4 or Na3PO4 media due to the active chlorine generation. A faster CPX degradation is reached when the current density is increased or the pH value is lowered. This last behavior may be ascribed to an acid-catalyzed reaction between HClO and CPX. Degradation rates of 22.5, 3.96, and 0.576 μmol L−1 min−1 were observed for DW, MWW and urine, respectively. The lower efficiency measured in these last two effluents was related to the presence of organic matter and urea in the matrix. A degradation pathway is proposed based on HPLC-DAD and HPLC-MS analysis, indicating the fast formation (5 min) of CPX-(S)-sulfoxide and CPX-(R)-sulfoxide, generated due the Cl2-active attack at the CPX thioether. Furthermore, antimicrobial activity elimination of the treated solution is reached once CPX, and the initial by-products are considerably eliminated. Finally, even if only 16% of initial TOC is removed, BOD5 tests prove the ability of electro-generated Cl2-active to transform the antibiotic into biodegradable compounds. A similar strategy can be used for the abatement of other recalcitrant compounds contained in real water matrices such as urine and municipal wastewaters. [Display omitted] •XRD and profile refinement indicate that Ti/RuO2-IrO2 forms a solid solution.•Ti/RuO2-IrO2 anode experienced a higher active chlorine production.•Cephalexin degradation on Ti/RuO2-IrO2 was carried out in urine and MWW.•Initial organic byproducts were identified, and pH and j evaluated.•Antimicrobial activity was removed and biodegradable byproducts were obtained.