Energy-Efficient Coaxial Electrocoagulation for Integrated Treatment of Urban Wastewater and Acid Mine Drainage: A Response-Surface Approach

This study determined the influence of experimental factors such as current density, surface-to-volume ratio (S/V), and contact time on the removal of Chemical Oxygen Demand (COD) and energy consumption during electrocoagulation, aiming to optimize the efficiency of a coaxial electrocoagulator for the co-treatment of municipal wastewater and acid mine drainage. After identifying the optimal volumetric ratio between both types of effluents, a Box–Behnken design and response-surface methodology were employed to identify the conditions that maximize COD removal while minimizing energy consumption. Under optimal conditions (current density of 2.42 A·m−2, S/V = 300 m2·m−3, 60 min), a COD removal of 91.13% was achieved with a specific energy of =2.59 kWh·kgCOD−1. The statistical model for COD removal demonstrated a good fit (R2 = 0.87), though its predictive power was limited (predicted R2 = 0.53). In contrast, the model for energy consumption exhibited an outstanding fit (R2 = 0.99) and high predictive consistency (predicted R2 = 0.98), confirming the decisive influence of current density on energy demand. Additionally, the S/V ratio emerged as the most impactful factor in COD removal variability. Overall, the findings highlight the importance of balancing removal efficiency with the economic feasibility of the process, contributing to the design of more sustainable and effective strategies for integrated wastewater treatment.