Partial Desalination of Saline Groundwater: Comparison of Nanofiltration, Reverse Osmosis and Membrane Capacitive Deionisation

Abstract

Saline groundwater (SGW) is an alternative water resource. However, the concentration of sodium, chloride, sulphate, and nitrate in SGW usually exceeds the recommended guideline values for drinking water and irrigation. In this study, the partial desalination performance of three different concentrated SGWs were examined by pressure-driven membrane desalination technologies: nanofiltration (NF), brackish water reverse osmosis (BWRO), and seawater reverse osmosis (SWRO); in addition to one electrochemical-driven desalination technology: membrane capacitive deionisation (MCDI). The desalination performance was evaluated using the specific energy consumption (SEC) and water recovery, determined by experiments and simulations. The experimental results of this study show that the SEC for the desalination of SGW with a total dissolved solid (TDS) concentration of 1 g/L by MCDI and NF is similar and ranges between 0.2–0.4 kWh/m3 achieving a water recovery value of 35–70%. The lowest SECs for the desalination of SGW with a TDS concentration ≥2 g/L were determined by the use of BWRO and SWRO with 0.4–2.9 kWh/m3 for a water recovery of 40–66%. Even though the MCDI technique cannot compete with pressure-driven membrane desalination technologies at higher raw water salinities, this technology shows a high selectivity for nitrate and a high potential for flexible desalination applications.