Enhancing Sustainability of Pollution Control with Electrochemical Oxidation Optimized by Alternating Polarity

Electrochemical oxidation is promising for pollution control with distinctive advantages in sustainability and effectiveness, particularly in aqueous environments high in salinity and hardness. However, electrode fouling, such as scaling, is shown as a critical limitation in this application. This study investigates the potential of alternating polarity as an in-situ strategy to mitigate electrode fouling while maintaining stable oxidation efficiency. Specifically, the work evaluates the effectiveness of alternating polarity in achieving a balance among fouling control, pollutant degradation, and energy consumption. In the first part, methylene blue was used as a surrogate in a continuous stirred tank reactor (CSTR) to optimize parameters including different electrode configurations (anode/cathode: Boron-Doped Diamond (BDD)/ graphite (Gr), Gr/Gr), polarity modes (constant polarity, alternating polarity), and polarity-exchange time (0.5hr, 2hr, 4hr). With constant polarity, electrochemical treatment of methylene blue exhibited an initial removal efficiency of 95%, which, however gradually declined with prolonged treatment beyond 0.5hr due to electrode fouling by scaling. In comparison, the use of alternating polarity resulted in sustained removal of methylene blue with the reduction in scaling by over 87% as well as the increase in the production of free chlorine as the oxidizing agent by 185%. Further testing of alternating polarity indicated that the exchange time of 2hr was optimal for sustained treatment efficiency and mitigation of electrode scaling. Moreover, the use of graphite as electrode material resulted in the reduction in energy consumption by 27% as compared with BDD as the electrode material. In the second part, a hydrophobic n-alkane (n-docosane) typical of petroleum produced water, was used as the target pollutant. Batch experiments were conducted to optimize the applied voltage (2, 4, 5V) and electrode configurations (BDD/BDD, BDD/Gr, Gr/Gr). Effective degradation was achieved at applied voltages above 4 V. Graphite electrodes exhibited strong affinity toward n-docosane, which facilitated the adsorption of the pollutant onto the electrode surface and promoted its subsequent electrochemical oxidation. Adsorption experiments revealed that equilibrium was reached within 6 hours with a capacity of 0.11 g(n-docosane) g(graphite)⁻¹. As a result, graphite-containing configurations achieved higher overall removal efficiency. Semi-CSTR tests were conducted under the optimized conditions determined in the first part. Under constant polarity, the removal efficiency of n-docosane declined from a peak of 86.3% at 48 hours to 58.7% at 120 hours, indicating progressive electrode deactivation and loss of treatment performance. In contrast, alternating polarity using the Gr/Gr configuration improved overall removal efficiency from 72.0% (constant polarity, BDD/Gr) to 85.7% and effectively prevented performance deterioration, although electrode corrosion was observed at high current densities for the Gr/Gr setup. Overall, this study demonstrates that sustainable application of alternating polarity–assisted EO requires an integrated strategy combining electrode material selection, optimized voltage operation, and carefully tailored polarity-exchange time to simultaneously achieve fouling mitigation, high degradation efficiency, and energy efficiency.