Removal of nitrate ion from water by electrochemical approaches

This study is focused on the mechanism of nitrate removal from aqueous solutions by electrochemical denitrification process (EDN) in an undivided electrolytic cell. The sacrificial (Fe and Al) electrodes and Inert (graphite (Gr)) electrode are employed for evaluation of operational parameters, namely current density, electrolysis time and sodium chloride concentration. The experimental results reveal that nitrate-N removal efficiency of 92% for Al-Fe (anode-cathode) and 80% for Fe-Fe are achieved at a current density of 25 mAcm(-2) and 180 min electrolysis time in 100 ppm of NaCl when the initial nitrate-N concentration is 100 ppm. However, during this process approximately 20 ppm of ammonia-N is also formed. Ammonia-N generated is significantly lower compared to the amount of nitrate-N removal. It can be attributed to the fact that nitrate ion can be removed by both electrocoagulation (EC) and electrochemical reduction (ER) processes simultaneously. Experiments using Al, Fe and Gr as cathodes as well as anodes indicate that the contribution of EC increases when dissolving anodes are used. Further confirmation of nitrate-N removal by EC pathway is obtained by quantitative estimation of nitrate present in the sludge. During EDN, pH of the solution also increases with ammonia generation. (C) 2015 Published by Elsevier Ltd.