Strategies for Nitrate and Nitrite Removal: Closing the Loop Using Membrane Electroreduction and Catalytic Reduction Processes

Abstract

The excessive use of fertilizers is the primary cause of increasing contamination of surface water and groundwater by nitrate ions. To address this problem, this study explores an optimized electroreduction method using a current-voltage approach to reduce nitrate ions. The nitrate electroreduction process employed a copper cathode (Cu) and titanium coated with titanium and ruthenium oxides (Ti/70TiO230RuO2) anode. The use of a current density beyond the limiting one promoted a greater reduction of nitrate. A current density of 3.5 mA/cm2 produced 91% nitrate reduction, resulting in 85 mg/L of N-Nitrite. Subsequently, the research investigates the use of electroreduction and catalytic processes for the treatment of this nitrite brine, aiming at high selectivity for gaseous compounds. To this end, active carbon fiber containing a Pd catalyst was employed. The electroreduction of nitrite achieved 28% and 36% reduction, using a Ti/70TiO230RuO2 anode and Ti/70TiO230RuO2 or Cu cathodes, respectively, at a current density of 2.3 mA/cm2, producing only ammonium ions. On the other hand, the use of nitrite catalytic reduction allowed the complete reduction of N-Nitrites, with high selectivity to gaseous nitrogen (97%). The combined approach of electrochemical reduction, using a current density above the limiting one, and catalytic reduction, with Pd-based carbon fibers, offers several benefits, including selectivity, efficiency, versatility, and sustainability. As such, it represents a promising strategy for the removal of nitrates from water with high selectivity to gaseous compounds, addressing an urgent environmental challenge.