Removal of persistent organic contaminants from wastewater using a hybrid electrochemical-granular activated carbon (GAC) system

Highlights: • Persistent contaminants removed by 3D ELOX reactor with bipolar GAC polarization. • Synergy of electrosorption and electrodegradation on GAC at high applied currents. • Lower amounts of ClO₃⁻ and ClO₄⁻ in 3D ELOX due to their electrosorption on GAC. • Lower amounts of chlorinated and iodinated organics in 3D ELOX. A three-dimensional (3D) electrochemical flow-through reactor equipped with GAC packed bed, polarized by the electric field, was evaluated for the removal of persistent organic contaminants from real sewage effluent. The performance of the reactor was investigated for 27 consecutive runs at two anodic current densities, i.e., low current density (LCD) of 15 A m⁻², and high current density (HCD) of 100 A m⁻². In the HCD experiments, the adsorption ability of saturated GAC was increased, mainly due to the increase in the mesoporosity of GAC. A synergy between electrosorption/adsorption on GAC and electrooxidation was observed in terms of the removal of all target pollutants. DEET presented the highest synergy, ranging from 40% to 57%, followed by iopromide (22–46%), carbamazepine (15–34%) and diatrizoate (4–30%). The addition of GAC decreased the concentrations of toxic chlorate and perchlorate by 2-fold and 10-fold, respectively, due to their electrosorption on GAC. Also, 3D electrochemical system yielded lower concentrations of adsorbable organic iodide (AOI) and adsorbable organic chlorine (AOCl). Thus, addition of low amounts of GAC in electrochemical systems may be a low-cost and simple way of minimizing the formation and final effluent concentrations of toxic halogenated byproducts.