Removal of meropenem from environmental matrices by electrochemical oxidation using Co/Bi/TiO2 nanotube electrodes

Abstract

Degradation of meropenem via electrochemical oxidation was investigated for the first time. A TiO₂ nanotube array (TiO₂ NTA) was modified by co-doping cobalt and bismuth (Co/Bi/TiO₂ NTA) to enhance the anode stability/lifetime and the generation of reactive oxygen species (ROS, e.g. ˙OH). A series of anodic oxidation tests were carried out to study the effects of operating parameters, including current density (4–12 mA cm⁻²) and presence of different ions (Cl⁻, HCO₃⁻, and SO₄²⁻), on the degradation of meropenem. With an applied current density of 10 mA cm⁻² and an initial concentration of 500 μg L⁻¹, ∼94% of meropenem was removed in 15 min. The presence of Cl⁻ and SO₄²⁻ accelerated meropenem degradation, while HCO₃⁻ suppressed the removal. The transformation products were also investigated using 2D-NMR and LC/MS, where C₇N₂O₂H₁₂ was identified as one of the main intermediates. Results from CV measurements and scavenger tests indicated that both direct degradation and indirect reaction via the formation of ROS contributed to meropenem removal. Electrochemical oxidation of meropenem (500 μg L⁻¹) was also evaluated in environmental matrices, where ∼77% removal (E_EO 6.988 kW h m⁻³) with ∼56% TOC mineralization and ∼73% removal (E_EO 9.026 kW h m⁻³) with ∼55% TOC mineralization were achieved in RO concentrate (10 mA cm⁻²) and secondary effluent (4 mA cm⁻²), respectively. According to the accelerated lifetime test results, the lifetime of Co/Bi/TiO₂ NTA anode under 40, 20, 10, and 5 mA cm⁻² can be estimated to be 1337, 5873, 25 806, and 113 383 hours, respectively, demonstrating the great potential of Co/Bi/TiO₂ NTA as a stable and cost-effective anode material for the removal of recalcitrant organic pollutants from environmental matrices.