The improvement on total nitrogen removal in nitrate reduction by using a prepared CuO–Co3O4/Ti cathode

In this work, a CuO–Co3O4/Ti composite was prepared via the coating-calcination method and employed as a cathode for the NO3−-N reduction to increase the removal efficiency of total nitrogen (TN). SEM, EDS, and XRD characterization results indicated that CuO and Co3O4 were successfully introduced to the surface of Ti. The CuO–Co3O4/Ti electrode eventually removed NO3−-N with the main products of N2, NH4+-N and NO2−-N. In comparison to the Co3O4/Ti electrode, the better hydrogen evolution properties of the CuO–Co3O4/Ti electrode resulted in pH increase and NH3 gas release, so the TN removal for CuO–Co3O4/Ti electrode was improved approximately 20%. The presence of Cl− with the concentration up to 1000 mg L−1 greatly promoted the removal of TN from 40.1% to 94.0%, as a result of NH4+-N oxidation with free chlorine produced from the anode. Furthermore, the CuO–Co3O4/Ti electrode was applied to conduct three types of actual wastewater (biological effluent of municipal wastewater and industrial wastewater, and a regeneration concentrate from an anion exchange process) for nitrate removal. The highest TN removal efficiency (78.5%) and current efficiency (54.5%), and the lowest energy consumption (2 × 10−4 kWh mg−1 TN) were obtained for the regeneration concentrate, suggesting the feasibility of the CuO–Co3O4/Ti electrode to the water with high conductivity and high Cl− concentration for removing TN by the reduction of nitrate.