Electrochemical oxidation of anesthetic tetracaine in aqueous medium. Influence of the anode and matrix composition

Abstract

The degradation of 150mL of 0.561mM tetracaine hydrochloride at pH 3.0 by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2) has been studied at a low current density of 33.3mAcm−2 in three different matrices: 0.050MNa2SO4, real urban wastewater and a simulated matrix mimicking its electrolyte composition. Comparative trials were performed in an undivided cell with a 3cm2 boron-doped diamond (BDD), Pt, IrO2-based or RuO2-based anode and a 3cm2 air-diffusion cathode that allowed continuous H2O2 electrogeneration. In 0.050MNa2SO4, much faster and overall removal of tetracaine occurred using BDD because of the large oxidation ability of BDD(OH) formed from anodic water oxidation. In either simulated matrix or real wastewater, the RuO2-based anode yielded the quickest tetracaine decay due to a large production of active chlorine from anodic oxidation of Cl−. For the mineralization of the organic matter content, the BDD/air-diffusion cell was the best choice in all aqueous matrices, always reaching more than 50% of total organic carbon abatement after 360min of electrolysis, as expected if BDD(OH) mineralizes more easily the chloroderivatives formed from tetracaine oxidation in the presence of active chlorine. The initial N of tetracaine was partly transformed into NO3−, although the total nitrogen of all solutions always decayed by the release of volatile by-products. In the Cl−-containing matrices, significant amounts of ClO3− and ClO4− were obtained using BDD, whereas active chlorine was much largely produced using the RuO2-based anode. Five aromatic by-products, one of them being chlorinated, along with low concentrations of oxalic acid were identified. The change in toxicity during EO-H2O2 with BDD in the sulfate and simulated matrices was also assessed.