Modular treatment of arsenic-laden brackish groundwater using solar-powered subsurface arsenic removal (SAR) and membrane capacitive deionization (MCDI) in Vietnam

Abstract

Abstract To evaluate energy efficient concepts for the modular treatment of brackish water, pilot trials for groundwater desalination and arsenic (As) removal were carried out in the Mekong Delta, Vietnam. Groundwater here is affected by naturally occurring high iron (Fe2+) and As concentrations, while, in coastal regions, groundwater is additionally contaminated by high salinity mostly due to seawater intrusion. Desalination was conducted by membrane capacitive deionization (MCDI), which shows low specific energy consumption (SEC). Anoxic groundwater with As(III) and Fe2+ was treated using a pre-oxidation step called subsurface arsenic removal (SAR) with the main advantage that no As-laden waste is produced. The pilot plant was operated using a photovoltaic system (3 kWp) and a small wind turbine (2 kWp). The SEC of drinking water produced was 3.97 kWh/m3. Total dissolved solids (TDS) of 1,560 mg/L were lowered to 188 mg/L, while Fe2+ was reduced from 1.8 mg/L to the below detection limit and As from 2.3 to 0.18 μg/L. The results show that SAR is a feasible remediation technique for Fe2+ and As removal in remote areas, and demonstrate the potential of MCDI for brackish water desalination coupled with renewable energies. However, improvements in energy demand of the MCDI module can still be achieved.