Superior reduction of nitrate with simultaneous oxidation of intermediates and enhanced nitrogen gas selectivity via novel electrochemical treatment

This study reports an electrochemical reduction of the NO3 − along with oxidation of the in-situ generated NH4 + with maximum selectivity of the N2 gas as the final product. The use of aluminum as a cathode and Ti/RuO2 as an anode showed enhanced electrochemical nitrate reduction at the cathode and oxidation of the ammonium ion at the anode. Effects of various parameters like initial NO3 − concentration (Co = 100−400 mg L−1), a dose of the Cl− as NaCl (NaCl = 100−400 mg L−1), current density applied (j = 83.3-333.3 A m−2), solution pH (pH = 4–10) and electrolysis time (t = 0−120 min) were studied in terms of NO3 − reduction and total nitrogen (TN) removal efficiencies. Current efficiency (CE) was elaborated with respect to end products like N2, NO2 − and NH4 +. Specific electrical energy consumption (SEC) was calculated in kWh kg−1 NO3 − removed for the electrochemical process. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were utilized for understanding the oxidation/reduction mechanism over electrodes and the characteristics of the electrodes in a different solution. The studied mechanism suggested a circular conversion of NO3 − through complex processes into the N2 gas as the final product. The ultimate nitrate and TN degradation efficiency of ≈95% with N2 selectivity of ≈100% were achieved at the optimum condition of Co = 100 mg L−1, NaCl = 300 mg L−1, j = 333.3 A m−2, pH = 6 and time = 120 min with SEC = 927.4 kW h kg−1 NO3 − removed.