Electrochemical removal of nitrate from wastewater with a Ti cathode and Pt anode for high efficiency and N2 selectivity

Abstract In this work, electrochemical denitrification using a Ti cathode and Pt anode was studied with the objective of enhancing the removal efficiency of NO3− and the selectivity of NO3− to N2. We first determined the optimal working potential and initial pH value for the activity and selectivity of NO3− removal by constant-potential electrolysis experiments; in this case, a working potential of −1.26 V and an initial pH value of 6 were optimal. Then, the anodic oxidation of the ammonia byproduct was investigated by varying the cathode/anode surface area ratios, suggesting that anodic oxidation played an important role in electrochemical denitrification. Under optimal conditions, the NO3− removal efficiency could reach 82.1% with a N2 selectivity of 81.3%; moreover, a current efficiency of 63.9% was achieved, surpassing most of the reported electrochemical denitrification processes. Additionally, in situ Fourier transform infrared (in situ FTIR) spectroscopy and cyclic voltammetry were used to determine the reduction mechanism. Results indicated that acidic conditions were suitable for direct and indirect nitrate reduction, while NO3− was mainly reduced via direct reduction under alkaline conditions; moreover, the reaction route of NO3− conversion was verified