Application of response surface methodology (RSM) for optimization and electrochemical oxidation of three mixed antibiotics at boron-doped diamond (BDD) electrodes

This study investigated hydrogen peroxide (H 2 O 2 ) supported electrooxidation using niobium-based boron-doped diamond (Nb/BDD) electrodes for the simultaneous removal of sulfanilamide (SN), tetracycline hydrochloride (TC-HCl), and sulfamethazine (SMZ) from biologically treated synthetic wastewater. Response surface methodology based on central composite design was applied to evaluate the effects of current density, pH, H 2 O 2 dose, and initial antibiotic concentration on removal performance. The selected operating condition provided a chemically relevant design space by capturing the effects of antibiotic speciation, oxidant generation, radical availability, and pollutant loading. The optimized condition was identified at a current density of 30 mA/cm 2 , pH 4.95, H 2 O 2 dose of 2.5 mM, and initial antibiotic concentration of 6000 µg/ L at 90 minutes. Under this condition, the model predicted removal efficiencies of 95.32%, 92.35%, and 86.16% for SN, TC-HCl, and SMZ, respectively, with an overall desirability of 0.817. Experimental validation confirmed removals of 97%, 95.50%, and 88%, respectively, which is an indication of good performance between predicted and observed values. TOC decreased from 85 to 20 mg/L after 90 min, corresponding to a mineralization efficiency of 76.47%, which confirmed that the process promoted better oxidation beyond parent-compound degradation. Under the optimized operating conditions, the process required 0.198 kWh to treat a 3.0 L batch, equivalent to a specific energy consumption of 66 kWh/m 3 and an estimated electrical cost of 6.51 CAD/m 3 . Overall, the findings demonstrate that H 2 O 2 -assisted Nb/BDD electrooxidation is an effective advanced treatment strategy for antibiotic-containing wastewater, particularly when simultaneous parent-compound removal and mineralization are required.