Denitrification and neutralization treatment by direct feeding of an acidic wastewater containing copper ion and high-strength nitrate to a bio-electrochemical reactor process

The feasibility of the direct denitrification treatment of copper metal pickling wastewater by using a bio-electrochemical reactor process was investigated experimentally. Carbon electrodes were installed in the reactor as the anode and cathode and denitrifying microorganisms were fixed on the surface of the cathode. The reactor was continuously operated by applying an electric current and feeding acetate. In this reactor, copper ion removal and denitrification proceeded simultaneously and the pH value of the treated water was increased almost to neutral. The electric current that passed through the cathode contributed to the removal of the copper ion and the generation of hydrogen gas. The generated hydrogen gas as well as the added acetate was effectively utilized for denitrification. A theoretical evaluation of pH in the effluent suggested that the pH increase was mainly caused by the generation of hydroxyl ion during denitrification. In addition, the inorganic carbon species generated during denitrification with acetate and by the electrochemical oxidation of anodic carbon acted as a buffer to minimize a further increase of pH at higher nitrate removal efficiencies. These results demonstrated that copper ion removal, denitrification and neutralization could be achieved simultaneously by using a single bioelectrochemical reactor.