Central composite rotatable design for non-convex optimization of removal efficiency of hydroxychloroquine in an electrochemical cell

Hydroxychloroquine sulfate (HCQ), an against-COVID-19 drug, is a dangerous organic compound in wastewater. In this study, 0.6 L of an HCQ solution (50 mg L−1) was electro-oxidized in a batch electrochemical cell (BEC) with two boron-doped diamond (BDD) electrodes. The optimal operating conditions were established by DoE-driven non-convex constrained optimization. A central composite rotatable design (CCRD) was applied to model the chemical oxygen demand (COD) removal efficiency and to evaluate the influence of current density (j): 10–120 mA cm−2, initial pH: 2–12, and stirring speed (Ω): 400–600 rpm. Experimental results were modeled by a reduced third-order polynomial function having a determination coefficient (R2), root mean square error (RMSE), mean square error (MSE), and coefficient of variation (C.V.) of 0.9906, 0.0460, 0.0021, and 3.72