Electrocoagulation of chromium in tannery wastewater by a composite anode modified with titanium: parametric and kinetic study

Abstract

ABSTRACT To overcome the color index problem of the iron electrode and guarantee the high treatment efficiency of chromium (Cr), this study used a titanium electrode to remove Cr from the synthetic and real tannery wastewater. The effects of electrode material, reaction voltage, pH value and reaction time on the removal efficiency of Cr ions were investigated by electrocoagulation (EC). The results demonstrate that (Al + Ti)–C composite electrode had a high Cr removal efficiency (98.88%) and did not increase the color index of effluent. The optimal EC conditions were the pH value of 6 and a voltage of 5 V that contributed to the around 100% current efficiency. Regarding the morphologies of Cr, a majority of removed Cr was accumulated in the residual sludge, and the Cr 3+ in wastewater was mainly formed by the combination of Cr and hydroxide, e.g. [Cr(OH) 2 + ] and [Cr(OH) 2+ ]. Finally, the kinetics of removing Cr and chemical oxygen demand by EC was in accordance with the pseudo-first-order kinetic model and pseudo-second-order kinetic, respectively. Overall, the composite anode modified by titanium to remove Cr can increase the treating effect without the increase of the color index.