Development of a continuous electrochemical reactor incorporated with waste-derived activated carbon electrode for the effective removal of hexavalent chromium from industrial effluent

Being a recognized carcinogen, hexavalent chromium is hazardous to both human and environmental health. Thus, it is imperative to regulate and oversee their levels in a variety of industries, including textiles, dyes, pigments, and metal finishing. This study strives to reduce Cr(VI) in wastewater by using capacitive deionization in conjunction with an activated carbon-based electrode and a continuous electrochemical reactor (CER). Activated carbon derived from rubberwood sawdust demonstrated excellent properties, including a high surface area of 1157 m² g^-1. The electrical conductivity and mechanical stability of the electrode were enhanced by the incorporation of synthesized expanded graphite (EG) into the AC. Key parameters were optimized via systematic batch electroreduction experiments with an optimal response surface design. The efficacy of the fabricated CER was proved when it successfully reduced Cr(VI) in a 5 mg L^-1 solution within 15 min under optimized conditions, in contrast to the considerably longer durations anticipated by conventional methods. Validation of these findings was done by treating industrial wastewater of 30 mg L^-1 in the CER. The electroreduction of Cr(VI) followed the Langmuir isotherm with a maximum capacity of 13.491 mg g^-1 and pseudo-second-order kinetics. These results indicate that the combined use of the modified AC electrode and CER holds potential as a sustainable and economical approach to effectively eliminate Cr(VI) from wastewater.