Hybrid electrochemical-granular activated carbon system for the treatment of greywater

Three-dimensional (3D) flow-through electrochemical reactor filled with granular activated carbon (GAC) was employed for the treatment of greywater. Polarization of GAC by the electric field, without the direct contact with the terminal current feeders, resulted in oxidant production and degradation of the adsorbed/electrosorbed contaminants. This in turn enabled electrochemical regeneration of GAC and an improved performance compared to a conventional two-dimensional (2D) electrochemical system. The synergy between electrooxidation and GAC adsorption enhanced the performance of the 3D system by up to 21% and 23% in terms of COD and TOC removal, respectively, compared to the summed up performances of GAC and 2D electrochemical systems operating separately. In long-term operation of the 3D system with a previously saturated GAC, the regeneration efficiency of GAC was increased from 42 to 65% over 31 consecutive runs. Disinfection efficiency was evaluated using Escherichia coli (E. coli), spores of Clostridium perfringens (SCP) and somatic coliphages (SOMCPH) as model organisms for pathogenic bacteria, protozoan surrogate and viruses, respectively. GAC could not remove any of the abovementioned microbial indicators. 2D and 3D electrochemical systems achieved similar log removals of E. coli (4.6–5.1 log), SCP (0.1–0.6 log) and SOMCPH (3.2–3.3 log). However, the proportions of viable cells from the total cells adsorbed onto the GAC was reduced from 72% to 22% when an electric field was applied, further confirming that electrochemical polarization of GAC caused the killing of the adsorbed microorganisms. Simultaneous adsorption/electrosorption and electrocatalysis in the GAC packed bed lowered the energy consumption from 46 kWh kg COD⁻¹ removed in conventional 2D system, to 30 kWh kg COD⁻¹ removed in the 3D electrochemical system, thus enabling significant savings in the operational costs.