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 solution, 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.