Anode passivation mitigation by homogenizing current density distribution in electrocoagulation

Electrode passivation is the most challenging technical problem in electrocoagulation (EC) water treatment process, but research on understanding and mitigating passivation evolution are still lacking. Herein, homogenization of current density (CD) distribution was found to be a critical factor in alleviating the anode passivation during EC process. Decreasing electrode area decelerated the growth of passivation layer on anode through homogenizing CD distribution, which was quantified by the ratios of CD distributed at the electrode edges and centers. When aluminum anode area decreased from 8 cm2 to 2 cm2 with a constant CD, the homogenization degree increased by 24.0%, and passivation was reduced by 24.3%. The depth profiles of passivated anodes confirmed the inhomogeneity of the anode passivation. Thicker passivation layers were observed at edges due to high CD distributions, which originated from the "edge effect" of electric field distribution between parallel plate electrodes. A facile strategy to homogenize CD distribution by splitting electrodes into smaller electrodes is then proposed for passivation mitigation, which can save energy consumption by 21.8% with unchanged removal efficiency. This study provides a unique insight into anode passivation mitigation and a feasible electrode design in EC.