Modular Treatment of Arsenic-Laden Brackish Groundwater Using Solar-Powered Membrane Capacitive Deionization (MCDI) (Vietnam)

To develop easy-to-implement and low-energy water treatment plants, pilot trials for groundwater desalination and arsenic removal were carried out at the Mekong Delta in Vietnam. Desalination was conducted by membrane capacitive deionization (MCDI), which can show low specific energy consumption (SEC) compared to other desalination technologies. Anoxic groundwater with elevated As(III) and dissolved iron (Fe(II)) was treated using a pre-oxidation/adsorption step called subsurface arsenic removal (SAR). The main advantage of the in situ SAR process is that no As-laden waste is produced. The two different qualities of the treated water from two different stages of the pilot plant can be used for various purposes and can be modularly adjusted in volume according to requirements. The pilot plant was operated using a solar PV system and a small wind turbine. Results show that SAR can reduce the As- and the Fe-concentration to below drinking water limits. The MCDI lowers the total dissolved solids (TDSs) concentration of 1560-188 mg/L. The overall process (well pump to product tap) needs an SEC = 3.97 kWh/m3, which is supplied (127%) by renewable energy.