Electrocoagulation Using a Hybrid Combination of Iron and Aluminum Electrodes with Asymmetric Polarity Reversal

This study explores the use of asymmetric polarity reversal (PR) in continuous electrocoagulation (EC) for removing silica and hardness using Fe/Al hybrid electrodes. Asymmetric PR takes advantage of aluminum’s tendency to undergo cathodic dissolution by alternating a “forward” current with cheaper iron anodes and a shorter reverse current with aluminum as the anode, as iron cathodes are not prone to dissolution. Adjusting the polarity reversal time (PRT) varied the relative dosing of the Fe and Al coagulants. Silica removal exceeded 95% across all asymmetric PRTs at a fixed charge loading of 2000 C L^–1, with energy consumption between 1.44 and 1.93 kWh m^–3. Symmetric 10 min PRT achieved 90% Ca and 75% Mg removal, outperforming direct current (DC) EC. Both asymmetric PRTs of 10 min (Fe) and 30 s (Al) and a symmetric PRT of 10 min (Fe/Al) achieved high contaminant removal and relatively low treatment costs while using different amounts of Fe and Al. These configurations also lowered the cell voltage due to reduced fouling and passivation. This hybrid EC with asymmetric PR offers a novel, cost-effective method for adjusting the performance and optimizing the cost of wastewater treatment.