Characterization of a flow-through electrochemical reactor for the degradation of ciprofloxacin by photoelectro-Fenton without external oxygen supply

Abstract

This work reports the experimental characterization of an innovative electrolyzer designed for self-sustained H2O2 production and synchronized degradation of the antibiotic ciprofloxacin (CIP) by photoelectro-Fenton (PEF) process tested in recirculation operation mode. The flow-through electrochemical reactor comprises an arrangement of two alternated anodes and cathodes, using the anodic O2 generated from water oxidation at Ti|IrO2-Ta2O5 anodes to produce H2O2 at graphite-felt cathodes from the oxygen reduction reaction (ORR). The influence of the most relevant operation conditions such as the initial Fe2+ concentration, applied current density, liquid flow rate (Q) and initial CIP concentration was systematically examined during the electrolytic trials by analyzing the CIP concentration decay, solution mineralization, and time course of Fe2+ content. It is demonstrated that the H2O2 concentration attained with this reactor configuration is sufficient to run the PEF treatment without needing an air pump or compressor. Complete elimination of CIP was reached at 40 min, with mineralization current efficiency and electrolytic energy consumption of 42% and 0.25 kWh (g TOC)-1, respectively. Oxalic and oxamic acids were the final organic by-products of the destruction of CIP, which also yielded nitrate, ammonium, and fluoride ions. PEF outperformed other processes like anodic oxidation with cathodic H2O2 and electro-Fenton (EF), as revealed by comparing the degradation and mineralization profiles.