Denitrification enhancement by electro-adsorption/reduction in capacitive deionization (CDI) and membrane capacitive deionization (MCDI) with copper electrode

The green and efficient removal of nitrate (NO3-) in groundwater is a primary concern nowadays, and membrane capacitive deionization (MCDI) is an emerging technology for the removal of nitrate (NO3-) from water. In this study, a novel electrochemical system for nitrate denitrification removal was established, wherein the economic non-noble metal copper was used as the electrode material to achieve harmless removal of nitrate in a single electrochemical cell. The effects of applied voltage, initial NO3- concentration, and co-existing matters on NO3- denitrification removal during electro-adsorption/reduction system were deeply investigated. The results showed that the NO3- denitrification removal increased with raised voltage and in proportion to the initial NO3- concentration within certain limits, wherein the removal rate reached a maximum of 53.3% in the single-solute solution of 200 mg L-1 NaNO3 at 1.8 V. Nevertheless, overhigh voltage or initial NO3- concentration would have a negative effect on nitrate removal, which was caused by multiple factors, including side reactions in the so-lution, fouling of activated carbon fiber and anion exchange membrane, and corrosion of copper electrode. The presence of NaCl also had a negative effect on the removal of nitrate, which was mainly caused by fouling of ACF/IEM and redox reaction on account of the chloride ions. This study provides a potential economical alternative for the NO3- denitrification removal to achieve a more environmentally friendly outcome.