Performance of Nb/BDD material for the electrochemical advanced oxidation of prednisone in different water matrix

Glucocorticoids are widely used to treat a variety of diseases. Consequently, these compounds have been found in water and wastewater matrix. Despite studies have proven its toxicity, just a few works investigate techniques to degrade and mineralize them. To solve this issue, this work presents the degradation and mineralization of prednisone (PRED) by electrochemical advanced oxidation (EAO) using a boron-doped diamond supported on niobium (Nb/BDD) anode in synthetic and real wastewater. Cyclic voltammetry (CV) was performed to investigate the PRED oxidation mechanisms. CV suggest that PRED will be oxidized via HO^• and other oxidants generated from the ions present in the liquid matrix (S₂O₈^2-, SO₄^•-, HClO, ClO^- etc.). Different EAO conditions as initial pH (3, 7 and 11) and applied current densities (5, 10 and 20 mA cm^-2) were evaluated. The best result was obtained at alkaline pH (11) and a current density of 20 mA cm^-2, achieving 78% of degradation and 42% of mineralization. Using the best conditions, the EAO was applied as a polishing treatment stage to remove PRED from a biological pre-treated municipal wastewater spiked with PRED. The results indicate that EAO applied in the real matrix provides better results than the synthetic solution, probably associated with the presence of ions that can be electrochemically converted into oxidant species, resulting in higher kinetic constant, mineralization current efficiency and lower energetic consumption. Therefore, the EAO process without the addition of chemicals has proven to be an effective alternative as a tertiary treatment of municipal wastewater contaminated with PRED.