Electrochemical oxidation of four pharmaceutical pollutants using Ti/IrO2 and Nb/BDD anodes: Application of factorial design methodology

The simultaneous oxidation of four PhCs (Carbamazepine (CBZ), Caffeine (CAF), Ibuprofen (IBU), and Diclofenac (DFC)) has been investigated by electrochemical oxidation process using Ti/IrO₂ and Nb/BDD anode electrodes, respectively. The initial concentration of each PhCs was 69 µg/L. The effectiveness of the electro-oxidation process was due to its capability of oxidizing PhCs at the anode surface and in solution. A factorial experimental design was used for determining the influent parameters on the PhCs degradation. Four factors were investigated: supporting electrolyte concentration, current density, period of electrolysis and anode type. Anode type and treatment time were the most influent parameters on the electrochemical degradation of pollutants. By using a 2⁴ factorial design, the best performance for PhCs degradation (more than 99 % of each PhC removed) was obtained by using boron doped diamond anode electrode (BDD) operated at a current density of 5.24 mA/cm² during 70 min of period treatment time in the presence of 1.0 g Na₂SO₄/L. However, the period of treatment time could be five times reduced (to simultaneously remove around 100 % of each PhC) while using NaCl as supporting electrolyte (instead of Na₂SO₄). This was mainly attributed to the combination of direct and indirect effect of electrolysis, more effective in the case of NaCl used as supporting electrolyte compared to Na₂SO₄. The direct effect of electrolysis contributed to oxidize 40–80 % of PhCs (namely for DFC, IBU and CAF), whereas more than 99 % of CBZ could be oxidized owing to the sole direct effect of electrolysis.