Electrochemical removal of nitrate ion from aqueous solution by pulsing potential electrolysis

The main problem in the process of the electrochemical removal of nitrate from aqueous solutions and wastewaters, when the electrolysis is performed at a constant potential, is the production of more toxic side-products than nitrates, such as NO2− and NH3. This work deals with the removal of nitrate by square, sinusoidal and triangular wave pulsing potential electrolysis. In this way, the nitrates are reduced during the cathodic cycle mainly to NO2− and NH3 and consequently, during the anodic cycle, the produced NO2− and NH3 are oxidized to NO3− and gaseous products, respectively.The experimental results on a Cu60Zn40 electrode showed that square asymmetrical pulses having a frequency of 50 Hz and duration in the cathodic and anodic limit of 80 and 20% of the period, respectively, are more effective than sinusoidal and triangular as regards to the removal efficiency (%RE) of nitrate.The minimum selectivity (%S) for both nitrite and ammonia was obtained in the frequency range of 30–50 Hz. At frequency values higher than 200 Hz the %RE of nitrate is decreased because the ions are not able to follow the potential changes and this leads to limited Faradaic reactions.When the electrolysis was performed by applying square pulses having a constant cathodic limit of −1.7 V versus Ag/AgCl and anodic limit ranged from 0.50 to 3.00 V, a minimum in the %S of nitrite and ammonia was observed at 1.50 V. This minimum was attributed to the ability of the formed surface oxides of brass to oxidize ammonia and nitrite.