Revealing degradation of organic constituents of urine during the electrochemical oxidation of ciprofloxacin via boron-doped diamond anode

Ciprofloxacin (CIP) is a widely prescribed fluoroquinolone antibiotic used to treat various types of infections, including respiratory and digestive diseases. However, after uptake, unmetabolized CIP is excreted through both urine and feces and persists in the aquatic environment due to its inefficient removal in municipal wastewater facilities. This accumulation causes potential risks to the health of living organisms. The present work reports a study on the remediation of CIP in synthetic urine by electrochemical oxidation (ECO) using an undivided cell with a boron-doped diamond (BDD) anode and a stainless-steel cathode. The heterogeneous hydroxyl radical BDD(^[rad]OH) formed at the anode surface from water discharge, remaining adjacent to it due to its short half-life time, and the powerful free chlorine formed from Cl⁻ oxidation were the pre-eminent oxidants. The influence of pH and current density (j) on CIP abatement was analyzed, rapidly attaining its overall removal at j ≥ 40 mA cm⁻² within the pH range 3.0–9.0 thanks to the action of free chlorine. The CIP decay always obeyed a pseudo-first-order reaction. The uric acid contained in the synthetic urine was completely oxidized, whereas a partial destruction was found for the major component urea and a smaller destruction of creatinine. A moderate TOC reduction slightly ≥ 40% was determined at pH 3.0 and 7.0 for j = 100 mA cm⁻². The main nitrogenated species released was NH₃ and small contents of residual free chlorine were finally detected. The present study reveals a good oxidation power of the ECO process with a BDD anode to remediate synthetic urine contaminated with CIP.