Desalination of Nakhon Ratchasima groundwater in Thailand by membrane capacitive deionization.

Abstract

A single-pass mode of membrane capacitive deionization (MCDI) stack unit was fabricated for alternative desalination in local brackish groundwater. Nakhon Ratchasima (Korat), Thailand, is in the northeastern region and mostly faced the salinity groundwater problem. A commercial coconut shell-based activated carbon (PAC) was used for electrode material due to an available and cost-effective choice. Comparing two different specific surface areas of PAC (1153 and 2145 m² g^-1) for the electrode material was studied regarding a basic electrosorption capacity. It revealed that the more hydrophilic surface of PAC and lower internal resistance, the higher electrosorption performance was observed, regardless of the specific surface area in the case of a similar pore structure. The MCDI stack unit with a large active area (16 × 16 cm²) of 80 pairs of electrodes (a large lab-scale unit) demonstrated a sufficient removal efficiency in single-pass mode to reduce salinity and hardness in Korat groundwater, composed of multi-coexisting ions (TDS ~ 2000 mg L^-1). A relative selectivity coefficient (RSC) demonstrated that highly charged cations with smaller hydrated ionic radii predominantly played a crucial role in removal efficiency. While the initial concentration was strongly affected by the same charged ions. Total removal efficiency (RE_total) and ion removal efficiency (RE_ion) revealed performance stability during 20 days of operation and produced purified water with acceptable standards for consumption. Finally, this finding demonstrated the possibility of applying the PAC1-MCDI stack unit for natural groundwater desalination with a satisfactory desalination performance. We hope that the data in this study can be beneficial guidance for further practical MCDI system improvement and setup in a local area of Thailand, dealing with the salinity groundwater problem. PRACTITIONER POINTS: Desalination of brackish groundwater by membrane capacitive deionization (MCDI). Hydrophilic surface of activated carbon materials predominantly influenced a higher electrosorption performance. Relative selectivity coefficient mainly relied on ionic charges and hydrated ionic radii. Using MCDI for local brackish groundwater desalination applications produced water safe for consumption.