Removal of nitrate using an activated rotating cylinder electrode

•Copper activated with cupric oxide is efficient for the reduction of nitrate to ammonia.•Periodical potential reversal is necessary to reactivate the cathodic surface.•A reactor with a rotating cylinder cathode is efficient for the removal of nitrate.

The removal of nitrate from a synthetic effluent, 30 mmol dm−3 KNO3 in 0.1 mol dm−3 K2SO4 as supporting electrolyte, is analysed by means of its reduction to ammonia using an undivided electrochemical reactor with a copper rotating cylinder cathode. The cathode was activated by a film of cupric oxide, anodically produced at a potential of 0 V against saturated calomel electrode, SCE. In some experiments, to avoid the deactivation of the cathode, a periodic potential reversal, PPR, technique was applied making the rotating electrode work 5 min as a cathode and 5 min in reactivation. The application of both strategies, cathode activation and the use of a PPR procedure, improved the reactor performance. Under these working conditions, with this specific synthetic effluent, ammonia was the main product of the reduction of nitrate obtaining a molar yield of 86% and a current efficiency of 90% with a nitrate conversion of 92% in an experiment of 1 h at −1.2 V, vs. SCE, as cathodic potential.