Lab-scale experiments with a monovalent ion selective membrane capacitive deionization for nitrate removal

Groundwater with high nitrate concentrations requires treatment before potable use. Conventional treatment methods such as nanofiltration and reverse osmosis can be used for desalination of most solutes. In contrast, a monovalent selective membrane capacitive deionization (mMCDI) can be used for selective nitrate removal. We use a nanofiltration membrane and anion exchange membranes with an additional neutral layer (AEM-Neutral) or a polyamide layer (AEM-PA) for selective nitrate removal with mMCDI by using a solution of mixed monovalent and polyvalent ions. Monovalent ion selectivity in short-term experiments is up to 17.3 with a nanofiltration membrane, up to 1.7 for AEM-Neutral and up to 5.2 for AEM-PA, whereby the specific energy consumption and water recovery depends on cell structure, applied electric voltage, flow rate and desorption time. Selective nitrate removal with AEM-PA or AEM-Neutral at 0.8 V demonstrated a specific energy consumption of 2 Wh g −1 removed nitrate, lower than pressure-driven membrane processes. • NF membranes are very selective towards nitrate but show a low removal efficiency. • Coated AEMs show a selectivity towards nitrate with a high removal efficiency. • mMCDI can be an alternative for NF/RO for nitrate removal in groundwater. • A low voltage and a high flow increase the monovalent ion selectivity in mMCDI.