Elimination of the antibiotic norfloxacin in municipal wastewater, urine and seawater by electrochemical oxidation on IrO₂ anodes

The electrochemical degradation of the fluoroquinolone antibiotic norfloxacin (NOR) on Ti/IrO₂ anodes, in several aqueous matrices was evaluated. For this purpose, initially the performance and degradation routes of the technology at several pH values (3.0, 6.5, 7.5 and 9.0) and in the presence of some of the most common anions in real water matrices (Cl^-, HCO₃^-, SO₄^2- and NO₃^-) were determined. The results showed that the degradation of NOR can occur through both direct elimination at the electrode surface and mediated oxidation, via the electrogeneration of oxidative agents, such as active chlorine species and percarbonate ions, which come from chloride and bicarbonate oxidation, respectively. Conversely, nitrate ions showed to inhibit the efficiency of the system. Concerning the pH, the efficiency of the process in the presence of chloride ions followed the order: 9.0>7.5>6.5>3.0; showing a strong dependence of the NOR speciation, and being the anionic form of the antibiotic the more susceptible to be oxidized. Furthermore, the identification of three primary NOR by-products demonstrated that the initial attack of the active chlorine species, mainly HOCl, occurred at the secondary amine of the piperazine ring followed by chlorination of the benzene ring. The precedent findings were crucial to understand the efficiency of the technology to eliminate NOR in synthetic complex matrices such as seawater, municipal wastewater and urine. The electrochemical oxidation showed to be promissory to eliminate NOR, and its associated antimicrobial activity, in such complexes matrices. Waters at basic pH containing chloride or bicarbonate ions, such as seawater or municipal wastewater showed to be the most adapted to the application of the technology. Additionally, nitrate ions or urea, found in some matrices like fresh urine, reduce the efficiency of the process.