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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. [ABSTRACT FROM AUTHOR]

2-Chlorophenol (2-CP) is a dangerous organic contaminant found in wastewater. In this work, 2.5 L of a 2-CP solution (1 mol/m3) was electrochemically treated in a flow-by reactor equipped with two boron-doped diamond electrodes (BDD) under batch recirculation mode for a period for 4 h, a current density of 0.14 A/cm2, a volumetric flow rate of 1 L/min, and pH = 7.3. In this work, a parametric mathematical model of the degradation efficiency of 2-CP was developed using an axial dispersion model and a continuous stirred tank for the flow-by reactor (FBR), which was constructed using a shell mass balance considering the dispersion and convection terms and the reservoir tank (CST), which was constructed using a mass balance of 2-CP. The parametric mathematic model of the electrochemical degradation of 2-chlorophenol was numerically resolved by employing the software package COMSOL Multiphysics® V. 5.3, where a mass transfer equation for diluted species and a global differential equation represents the FBR and CST, respectively. The results indicate that the parametric mathematical model proposed in this research fits the experimental results, and this is supported by the index performance values such as the determination coefficient (R2 = 0.9831), the mean square error (MSE = 0.0307), and the reduced root-mean-square error (RMSE = 0.1754). Moreover, the degradation efficiency of 2-CP estimated by the proposed model achieves 99.06%, whereas the experimental degradation efficiency reached 99.99%, a comparative error of 0.93%. This corroborates the predictive ability of the developed mathematical model and the effectiveness of the employed electrooxidation process. Finally, a 0.143 USD/L total operating cost for the electrochemical plant was estimated. [ABSTRACT FROM AUTHOR]