Performance comparison of electrocatalytic and photoelectrocatalytic oxidation processes for the treatment of real pharmaceutical wastewater: Mechanistic insights and acute toxicity assessment

Abstract

The treatment of real pharmaceutical wastewater remains a major challenge due to its highly complex composition, strong matrix effects, and associated toxicity. In this study, a real industrial pharmaceutical wastewater was treated using electrocatalytic oxidation (ECO) and photo electrocatalytic oxidation (PECO) processes employing Zn/TiO2-coated stainless-steel electrodes. The performance of the two processes was systematically evaluated and compared under identical operating conditions. Response Surface Methodology (RSM) was applied to optimize key operational parameters, including initial pH, applied current density, reaction time, and temperature. The developed models successfully predicted COD and UV254 removal efficiencies with high accuracy (R-2>0.98), revealing strong interaction effects among operational variables. Principal Component Analysis (PCA) was further employed to elucidate multivariate relationships, identifying COD, UV254, and current density as the dominant contributors to process variability. Among the tested configurations, the PECO system using a Zn/TiO2-TiO2 electrode pair exhibited superior performance, achieving maximum removal efficiencies of 78.78 % COD and 71.75 % UV254. Acute toxicity assessment using Daphnia magna demonstrated a substantial improvement in effluent quality, with immobilization decreasing from 97 % to 28 % after PECO treatment. A strong correlation between UV254 reduction and toxicity abatement was observed, indicating that UV254 may serve as a useful indicative parameter for tracking ecotoxicity changes within this specific system. This study presents a comparative and integrated evaluation of ECO and PECO processes for real pharmaceutical wastewater, combining advanced electrode design, statistical optimization, multivariate analysis, and ecotoxicological assessment. The results highlight the critical role of photo-assisted electrocatalysis and process optimization in achieving effective pollutant removal and toxicity reduction under realistic industrial conditions.