Direct Treatment of an Acidic and High‐Strength Nitrate‐Polluted Wastewater Containing Heavy Metals by Using a Bio‐electrochemical Reactor

Abstract

AbstractThe fundamental performance of a bio‐electrochemical reactor for treatment of metal pickling wastewater was investigated experimentally. A carbon anode and cathode were installed in the reactor. On the cathode, denitrifying microorganisms were immobilized. Continuous experiments were carried out by feeding a synthetic wastewater containing nitrate and binary heavy metal ions (copper and lead) at different loads and current densities. Acetate was added at 1.0 of C/N mass ratio which was less than the stoichiometric amount for the overall denitrification reaction. Experimental results indicated that the dissolved copper and lead removal, denitrification, and neutralization, could be achieved simultaneously in a single bio‐electrochemical reactor. Dissolved heavy metals were removed by electrochemical deposition on the cathode and by other phenomena such as the formation of insoluble suspensions and sorption on suspended bacterial sludge. Denitrification proceeded effectively with the utilization of both the added acetate and the hydrogen gas generated by electrolysis of water. The pH value increased close to neutral value due to the occurrence of denitrification, although the influent pH was less than 3. The removal efficiencies of heavy metals and nitrate increased with an increase in the current density. The denitrification rate decreased with increasing lead loading. The electric current was indispensable for sustaining stable treatment in the reactor.