Data-Based Modeling, Multi-Objective Optimization, and Multi-Criterion Decision-Making to Maximize the Electro-Oxidation of Metoprolol over Boron-Doped Diamond Electrodes in a Flow-By Reactor

Metoprolol is a cardioselective beta-blocker drug often used to treat hypertension, but it is considered as a hazardous organic persistent contaminant in wastewater. In this study, a 2.5 L solution of metoprolol (50 mg/L) underwent electro-oxidation in a flow-by reactor using boron-doped diamond electrodes in the batch recirculation mode. The study used multi-objective optimization and multi-criterion decision-making to determine the optimal operating parameters. The response surface methodology and a central composite rotatable design were used with three factors (pH0: 5–8, I: 2.5–4 A, and Q: 0.8–1.7 L/min) to model the chemical oxygen demand’s (COD’s) removal efficiency and the total organic carbon’s (TOC’s) removal efficiency. The experimental responses were modeled by reduced third- and second-order polynomials with determination coefficients (R2) of 0.9816 and 0.9430. The optimal operating parameters were found to be pH0 5, an I value of 3.84 A, and a Q value of 0.8 L/min with an electrolysis time of 7.5 h, resulting in a maximum COD removal efficiency of 60.8% and a TOC removal efficiency of 90.1%. The specific energy consumption was calculated as 9.61 kWh/mg of TOC, with a total operating cost of 0.77 USD/L. In conclusion, this study showed that the electrochemical process is efficient and reliable for treating wastewater containing metoprolol.