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A Co/Ti electrode for nitrate reduction was prepared by electrode-deposition. In the single-compartment electrolysis cell, nitrate (100 mg/L) removal reached nearly 100% after 3 h electrolysis under the current density of 20 mA cm–2 by using the Co/Ti electrode as cathode, and the main reduction products were ammonium nitrogen (66.5%) and nitrogen gas (33.5%). This performance on nitrate removal was comparable to a Co3O4/Ti electrode, and the electroactivity of the Co/Ti electrode towards nitrite reduction was higher than that of a Co3O4/Ti electrode. The Co/Ti electrode exhibited an improved stability with 18.7% of mass loss and 25.5% of Co dissolution compared with the Co3O4/Ti electrode after ultrasonic interference. The presence of chlorine ion (1,000 mg/L) could promote the total nitrogen (TN) removal to approximately 100% after 3 h electrolysis because of the ammonium oxidation by the free chlorine produced from the anode. In the presence of calcium (50 mg/L) and phosphate (0.5 mg/L), the nitrate removal decreased from 85.4 ± 1.5 to 57.7 ± 3.5% after ten reuse cycles. This result suggests that Ca and P should be pre-removed before the electro-reduction of nitrate. HIGHLIGHTS Co/Ti electrode was prepared by electrode-deposition with nitrate removal of nearly 100%.; The Co loss was improved comparing with the electrode prepared by thermal decomposition.; The higher electroactivity towards nitrite reduction led to no nitrite detected.; Ca and P decreased the nitrate removal for its precipitation onto the electrode.

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.