Optimization of the electrochemical degradation process of the antibiotic ciprofloxacin using a double-sided β-PbO2 anode in a flow reactor: kinetics, identification of oxidation intermediates and toxicity evaluation

Abstract

The electrochemical degradation of ciprofloxacin-CIP (50 mg L in 0.10 mol L NaSO) was investigated using a double-sided Ti-Pt/β-PbO anode in a filter-press flow reactor, with identification of oxidation intermediates and follow-up of antimicrobial activity against Escherichia coli. The effect of solution pH, flow rate, current density, and temperature on the CIP removal rate was evaluated. All of these parameters did affect the CIP removal performance; thus, optimized electrolysis conditions were further explored: pH = 10, q = 6.5 L min, j = 30 mA cm, and θ = 25 °C. Therefore, CIP was removed within 2 h, whereas ~75% of the total organic carbon concentration (TOC) was removed after 5 h and then, the solution no longer presented antimicrobial activity. When the electrochemical degradation of CIP was investigated using a single-sided boron-doped diamond (BDD) anode, its performance in TOC removal was similar to that of the Ti-Pt/β-PbO anode; considering the higher oxidation power of BDD, the surprisingly good comparative performance of the Ti-Pt/β-PbO anode was ascribed to significantly better hydrodynamic conditions attained in the filter-press reactor used with this electrode. Five initial oxidation intermediates were identified by LC-MS/MS and completely removed after 4 h of electrolysis; since they have also been determined in other degradation processes, there must be similarities in the involved oxidation mechanisms. Five terminal oxidation intermediates (acetic, formic, oxamic, propionic, and succinic acids) were identified by LC-UV and all of them (except acetic acid) were removed after 10 h of electrolysis.

Ciprofloxacin removal: BDD anode coupled with solid polymer electrolyte and ultrasound irradiation

“…The same phenomenon was observed by Klidi and co-workers when high current intensity is applied [53], due to the high rate of generation of hydroxyl radicals. Unreacted hydroxyl radicals form hydrogen peroxide and hydroperoxyl radical, with less oxidation power than •OH, reducing the mineralization efficiency [54]: The solution pH significantly affects the degradation rate (the higher the pH, the greater this rate), as recently demonstrated by the electrochemical degradation of CIP (50 mg L −1 in 0.10 mol L −1 Na 2 SO 4 ) in a filter-press flow reactor, using a double-sided Ti-Pt/β-PbO 2 anode [47]. The higher removal at higher pH was related to the two pK a values presented by CIP: 6.1 (carboxyl group) and 8.7 (nitrogen of the piperazine group).…”

“…The electrogeneration of hydroxyl radicals is one of the most promising AOPs. CIP (50 mg L −1 in 0.10 mol L −1 Na 2 SO 4 ) disappearance was recently attained in 2 h by a double-sided Ti-Pt/β-PbO 2 anode in a filter-press flow reactor, while 75 % of Total Organic Carbon (TOC) was removed after 5 h [47]. The same antibiotic (30 mg L −1 ) has been completely removed and TOC has been reduced to 30 % by the use of a SnO 2 -Sb/Ti mesh anode in 2 h at 30 mA cm −2 [48].…”

Recent Trends in Pharmaceuticals Removal from Water Using Electrochemical Oxidation Processes

“…A flow reactor equipped with a Ti-Pt/β-PbO 2 anode electrode was studied towards the electrochemical removal of 50 mg/L CFX using 0.1 M Na 2 SO 4 as the supporting electrolyte by Wachter et al [57]. Complete CFX removal was achieved after 2 h of treatment, where after 5 h, the TOC removal was equal to 75%.…”

Hazardous wastes treatment technologies

“…Dividing the electrochemical cell with a membrane improved molecule degradation, degree of mineralization and current efficiency. Wachter et al (2019) reported the degradation of ciprofloxacin‐CIP (50 mg/L in 0.1 M Na 2 SO 4 ) using a double‐sided Ti‐Pt/beta‐PbO 2 anode in a filter‐press flow reactor, while monitoring the antimicrobial activity exemplified by E. coli . The optimal electrolysis conditions were explored at pH 10, flow rate = 6.5 L/min, applied current = 30 mA/cm 2 .…”