Practical considerations for the electrochemical denitrification of real wastewater

Abstract

High concentrations of nitrate (NO₃⁻) in water is a serious threat to the environment and human health. Therefore, there is an urgent to explore and develop real wastewater treatment methods. In this study, the electrochemical reduction of NO₃⁻ using brass as the cathode and IrO₂–RuO₂/Ti as the anode was studied, and the influence of various conditions, including the current density, conductivity, initial pH, Cl⁻ concentration and, coexisting matter (PO₄³⁻, CO₃²⁻, Ca²⁺, and organics), were systematically investigated. The optimized method was verified for the reduction of NO₃⁻ in simulated wastewater and real wastewater. It was found that in the presence of 500 mg L⁻¹ Cl⁻, a reduction rate above 80% could be readily achievable for 50 mg L⁻¹ NO₃⁻–N in 100 min electrolytic treatment at a current density of 10 mA cm⁻². The presence of CO₃²⁻ and Ca²⁺ had no significant effect on NO₃⁻ reduction, but the presence of PO₄³⁻ could substantially decrease the reduction rate of NO₃⁻–N due to the competitive adsorption of HPO₄²⁻ and H₂PO₄⁻ on the brass electrode. The interference from PO₄³⁻ could be largely alleviated by the addition of Ca²⁺ to the sample solution. The presence of organic matters also adversely influenced the reduction rate of NO₃⁻–N, whereby the reduction rate of NO₃⁻–N decreased to 71.1% in a solution with 200 mg L⁻¹ COD. As the organic matter could be degraded in prolonged electrolytic treatment, our method showed good adaptability for real water treatment. The results obtained in the present study demonstrated that the electrolytic method with brass as the cathode and IrO₂–RuO₂/Ti as the anode not only had a satisfactory efficiency for NO₃⁻–N removal but also exhibited good durability in real water treatment.