Insight into BDD electrochemical oxidation of florfenicol in water: Kinetics, reaction mechanism, and toxicity

Antibiotics in the environment provoke serious consequences on living beings and can be effectively remediated by prominent advanced oxidation process. In this study, electrochemical advanced oxidation treatment in a lab-scale reactor for the degradation of florfenicol (FLO) was studied with the aid of boron-doped diamond anode (BDD). The results exhibited that the FLO degradation follows pseudo-first-order kinetics. As the current intensity rose from 60 mA to 250 mA, the FLO removal efficiency increased and the corresponding reaction rate constant increased from 0.0213 to 0.0343 min⁻¹, which was likely due to the more efficient participation of free hydroxyl radical (^•OH) generated at the BDD anode. Faster degradation and higher mineralization of electrolyzed FLO solution were achieved at higher current intensity as well as in higher SO₄²⁻ concentration medium, as a consequence of catalytic participation of oxidants (free ^•OH as well as sulfate radical (SO₄^•−) and persulfate (S₂O₈²⁻)). The increase in FLO concentration from 30 to 50 mg L⁻¹ resulted in a reaction rate constant decrease (from 0.0235 to 0.0178 min⁻¹). Eight transformation by-products (m/z = 372.99, 359.8, 338.0, 324.04, 199.00, 185.02, 168.99 and 78.989) and three inorganic ions (NO₃⁻, Cl⁻ and F⁻) were analyzed by UPLC‒Q‒TOF‒MS/MS and Ion‒chromatography, respectively. The Vibrio fischeri bioluminescence inhibition revealed an increase of toxicity during the electrochemical oxidation that could be attributed mostly to the generated organic chlorinated by-products (m/z = 372.99, 359.8) and inorganic species (ClO₂⁻ and ClO₃⁻).