Kinetics of nitrate reduction with the packed bed iron bipolar electrode

• Electrochemical nitrate reduction kinetics with ZVI-BP electrode were investigated.
• ZVI-BP electrode system had high faradaic current and current efficiency.
• Ammonia oxidation was related with catalytic oxidation and paired electrolysis.
• Magnetite was corrosion product of the ZVI-BP electrode.
• Nitrate reduction modeling can help to design the scale-up reactor.

This study investigated the kinetics of nitrate reduction with the zero-valent iron bipolar (ZVI-BP) electrode. The kinetics of the nitrate reduction was considered with respect to the initial concentration of nitrate and the flow rate. Increasing the initial concentration of nitrate enhanced the nitrate reduction rate and there was the proper flow rate (20 mL/min) to achieve the highest nitrate reduction rate (6.2 h−1). But increasing the initial nitrate concentration rather decreased conversion ratio of nitrate to ammonia from 54.5% to 45.9% because of the ammonia oxidation to nitrogen gas as electro-catalytic oxidation. The highest reaction rate was obtained when the experimental hydraulic retention time (HRT) was analogous to the theoretical HRT. The current efficiency was over 100% because of low current density and the redox reaction with Fe2+/Fe3+ redox couple. The corrosion of the ZVI-BP electrodes was characterized by using the X-ray Diffraction (XRD) and the field emission scanning electron microscope (FE-SEM). Magnetite was the major corrosion product and it had potential to enhance the nitrate reduction. The modeling of nitrate reduction had similar trend with experimental data and the verification of the modeling parameter will help the up-scale design of the system.

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