Nitrate reduction by electrochemical processes using copper electrode: evaluating operational parameters aiming low nitrite formation

This work aims to present different electroreduction and electrocatalytic processes configurations to treat nitrate contaminated water. The parameters tested were: current density, cell potential, electrode potential, pH values, cell type and catalyst use. It was found that the nitrite ion is present in all process variations used, being the resulting nitrite concentration higher in an alkaline pH. The increase in current density on galvanostatic operation mode provides a greater reduction of nitrate (64%, 1.4 mA cm−2) if compared to the potentiostatic (20%) and constant cell potential (37%) configurations. In a dual-chamber cell the nitrate reduction with current density of 1.4 mA cm−2 was tested and obtained as a NO3− reduction of 85%. The use of single chamber cell presented 32 ± 3% of nitrate reduction, indicating that in this cell type the nitrate reduction is smaller than in dual-chamber cell (64%). The presence of a Pd catalyst with 3.1% wt. decreased the nitrite (1.0 N-mg L−1) and increased the gaseous compounds (9.4 N-mg L−1) formation. The best configuration showed that, by fixing the current density, the highest nitrate reduction is obtained and the pH presents a significant influence during the tests. The use of the catalyst decreased the nitrite and enhanced the gaseous compounds formation. Highlights Electroreduction can be used to treat contaminated water with a high nitrate concentration.; Galvanostatic mode promotes a high nitrate reduction.; Increase in current density improves the nitrate reduction.; The Pd catalyst decreases the nitrite and increases the formation of the gaseous compounds.; This system does not need a catalyst separation stage of water after reaction.