Influence of anode material on electrochemical oxidation for the treatment of tannery wastewater

The treatment of tannery wastewater by electrochemical oxidation, mediated by an electro-generated species was carried out under galvanostatic conditions in an electrochemical reactor equipped with anodes based on noble metals and metal oxides (Ti/Pt–Ir, Ti/PbO2, Ti/PdO–Co3O4 and Ti/RhOx–TiO2). The decrease in time of chemical oxygen demand, nitrogen (TKN and ammonia), Cr and sulphides was monitored. The study showed that the rate of pollutant removal was significantly influenced by the type of anode material and electrochemical parameters. Different mechanisms contributed to the removal of pollutants when the reactor operated under conditions close to the limiting current for chlorine evolution and under much higher current density, with the reactor performing better at a high current/voltage. The kinetic pseudo-first order model applied for the interpretation of the results showed that the Ti/Pt–Ir and Ti/PdO–Co3O4 anodes performed better than the other two electrodes under the majority of tested conditions, with the highest rate of removal obtained for ammonia (kinetic rate constant ). Electrochemical oxidation can be applied as a post-treatment after the conventional biological process in order to remove the residual ammonia with low energy consumption (0.4 kWh m−3).