The effect of the supporting electrolyte on the electrooxidation of enrofloxacin using a flow cell with a BDD anode: Kinetics and follow-up of oxidation intermediates and antimicrobial activity

The role of the supporting electrolyte - SE (Na2SO4; NaCI; Na2CO3; NaNO3; Na3PO4 - 0.1 M ionic strength) in the galvanostatic (10 mA cm(-2)) electrochemical degradation of the fluoroquinolone antibiotic enrofloxacin (ENRO; 100 mg L-1) using a filter-press flow cell with a boron-doped diamond anode was investigated (flow rate, solution volume, and temperature were kept fixed at 420 L h(-1), 1.01, and 25 degrees C, respectively). The electrochemical degradation performance with the different SEs was assessed by following up [ENROL total organic carbon concentration (TOC), oxidation intermediates (detected by LC and LC QqTOF), and antimicrobial activity towards Escherichia coli as the electrolyses progressed. With NaCI as SE, complete removal of ENRO was attained similar to 10 times faster than with the other salts. The determination of terminal oxidation intermediates (short-chain carboxylic acids) produced during the electrolyses allowed concluding that their nature and number is indeed affected by the salt used as SE, most probably due to distinct electrogenerated oxidants. With NaCI, the antimicrobial activity of the electrolyzed solution decreased gradually (to similar to 20%) from 8 to 16 h of electrolysis due to the cleavage of the fluoroquinolone structure. On the other hand, with Na2SO4, Na2CO3 and NaNO3 as SEs the growth of Escherichia coli cells was observed only after similar to 14 h, whereas it was completely inhibited with Na3PO4. Clearly, the electrooxidation and mineralization of ENRO is strongly affected by the SEs used, which determine the degradation mechanism and, consequently, the removal rates of the solution's organic load and antimicrobial activity. (C) 2018 Elsevier Ltd. All rights reserved.