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
Advanced Oxidation Technologies: State-of-the-Art in Ibero-American Countries
The electrochemical degradation of ciprofloxacin—CIP (50 mg L−1 in 0.10 mol L−1 Na2SO4) was investigated using a double-sided Ti-Pt/β-PbO2 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, qV = 6.5 L min−1, j = 30 mA cm−2, 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-PbO2 anode; considering the higher oxidation power of BDD, the surprisingly good comparative performance of the Ti-Pt/β-PbO2 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.
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The research funding agencies CNPq, Capes, and FAPESP—São Paulo Research Foundation (grant numbers 2009/17138-0, 2009/54040-8, and 2012/13002-9) are gratefully acknowledged for financial support and scholarships. The pharmaceutical company EMS is also gratefully acknowledged for supplying samples of CIP hydrochloride monohydrate.
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