Electrochemical degradation of β-blockers. Studies on single and multicomponent synthetic aqueous solutions

As far as we know, this is the first study reporting the electrochemical decontamination of solutions containing β-blockers, which are pharmaceutical pollutants with a high occurrence in natural waters. The oxidation ability of two pre-eminent, eco-friendly electrochemical advanced oxidation processes (EAOPs), namely anodic oxidation (AO) and electro-Fenton (EF), has been compared at lab-scale by carrying out bulk electrolyses at pH 3.0 at constant current using a carbon-felt cathode able to electrogenerate H2O2 in situ. The studies of single component aqueous solutions were focused on atenolol as a model β-blocker. The AO process was proven much more effective using a large surface area boron-doped diamond (BDD) anode than a Pt one, which was explained by the great amount of active hydroxyl radicals (BDD(OH)) and the minimization of their parasitic reactions. The EF process with a Pt anode and 0.2 mmol l−1 Fe2+ showed even higher performance, with fast destruction of atenolol following pseudo-first order kinetics and fast mineralization because the oxidation process in the bulk allows overcoming the mass transport limitations. The time course of the concentration of the aromatic and short-chain carboxylic acid intermediates demonstrated the progressive detoxification of the solutions. Almost 100% of the initial N content was accumulated as NH4+. Multicomponent solutions containing atenolol, metoprolol, and propranolol, which usually occur together in the aquatic environment, were treated by EF using the Pt/carbon felt cell. A high mineralization rate was observed up to the overall total organic carbon (TOC) removal, which allowed reducing the energy consumption. The absolute rate constant for the reaction of each β-blocker with OH was determined and the reactivity was found to increase in the order: atenolol (1.42 × 109 l mol−1 s−1) < metoprolol (2.07 × 109 l mol−1 s−1) < propranolol (3.36 × 109 l mol−1 s−1).