LAUSR

A combined anode, Ti/IrO2 (0–3.5 h)–Ti/RuO2 (3.5–7 h) is designed to promote the removal of high concentration of nitrate by a stepwise method. During the electrolysis process, Ti/IrO2 is used as anode at the first stage to promote the generation of ammonia-N and then Ti/RuO2 is switched as anode at the next stage to enhance the chlorine evolution. The generated Cl2 will further react with H2O to produce ClO−, which will oxidize ammonia-N to N2, therefore improve the nitrate removal efficiency. Results shown that both of the reduction of nitrate and oxidation of the by-product of ammonia-N are enhanced and the total nitrogen removal efficiency is 85% when the initial nitrate concentration is 500 mg L−1. The avoid using cation exchange membrane not only efficiently reduces the operation cost but also simplifies the operation and maintain procedure.Graphical Abstract