Electrochemical Fenton-based treatment of tetracaine in synthetic and urban wastewater using active and non-active anodes.

The electrochemical degradation of tetracaine hydrochloride has been studied in urban wastewater. Treatments in simulated matrix with similar ionic composition as well as in 0.050 M NaSO were comparatively performed. The cell contained an air-diffusion cathode for HO electrogeneration and an anode selected among active Pt, IrO-based and RuO-based materials and non-active boron-doped diamond (BDD). Electrochemical oxidation with electrogenerated HO (EO-HO), electro-Fenton (EF) and photoelectro-Fenton (PEF) were comparatively assessed at pH 3.0 and constant current density. The pharmaceutical and its byproducts were oxidized by OH formed from water oxidation at the anode surface and in the bulk from Fenton's reaction, which occurred upon addition of 0.50 mM Fe in all media, along with active chlorine originated from the anodic oxidation of Cl contained in the simulated matrix and urban wastewater. The PEF process was the most powerful treatment regardless of the electrolyte composition, owing to the additional photolysis of intermediates by UVA radiation. The use of BDD led to greater mineralization compared to other anodes, being feasible the total removal of all organics from urban wastewater by PEF at long electrolysis time. Chlorinated products were largely recalcitrant when Pt, IrO-based or RuO-based anodes were used, whereas they were effectively destroyed by BDD(OH). Tetracaine decay always obeyed a pseudo-first-order kinetics, being slightly faster with the RuO-based anode in Cl media because of the higher amounts of active chlorine produced. Total nitrogen and concentrations of NH, NO, ClO, ClO and active chlorine were determined to clarify the behavior of the different electrodes in PEF. Eight intermediates were identified by GC-MS and fumaric and oxalic acids were quantified as final carboxylic acids by ion-exclusion HPLC, allowing the proposal of a plausible reaction sequence for tetracaine mineralization by PEF in Cl-containing medium.