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.

Assessing the suitability of desalination techniques for hydraulic barriers

“…2). Since CAPEX has the highest cost component in total costs of ED (details in Table 2 | Saline groundwater (SGW) composition and target characteristics for desalination within ADR Parameter SGW 13,14,26 Drinking water regulation 23 Guidelines for recharge/irrigation 15,24,25 TDS [mg/L]/ Electrical Conductivity [mS cm −1 ] 1000-20,000 mg L −1 ; 1000-20,000 mS cm −1 usually <600 mg L −1 should be similar to present freshwater conditions, (<450 mg L −1 , <0.7 mS cm −1 , preferable no deionised water) Sodium Adsorption Ratio [−] 1.5-25.0 no data available <10, depending on electrical conductivity and crop resistance…”

“…Comparative desalination techniques and case studies NF, RO, and ED are standard brackish water desalination technologies and are therefore included in our comparative analysis. Even though, CDI is examined mostly in laboratory scale and is controversy discussed in the literature 61,[68][69][70] , we included CDI and MCDI as potentially suitable technology in our study due to a high retention of sodium chloride 13,71,72 , recent economic analyses 52,62,63 and increasing interest in this technology 73 . A literature study for costs and SEC for brackish water desalination demonstrate the suitability of the preselected desalination technologies according to the before described requirements according quantity (>100 L d −1 ), quality (25% < R NaCl < 90%) and SEC (generally <2.5 kWh m −3 ).…”

“…Saline groundwater effected by seawater intrusion usually show a sodium chloride concentration exceeding the drinking water and irrigation limit values 13,14 . SGW is classified in slightly, moderately, highly and very highly SGW due to their electrical conductivity or chloride concentration 15,16 (Table 1).…”

“…Referring to Escalante et al 21 , so far there exists no general guidelines or fixed limit concentrations for sodium and chloride concentrations for managed aquifer recharge. According to this publication and van der Bruggen 22 , the target concentration produced by desalination should meet regional conditions for optimal recharge and final use as the limit quality for drinking water 23 and irrigation 13,24 (Table 2). According to Martin 25 , the concentration for recharge water should equal the natural composition of the initial present freshwater concentration to reduce swelling, dissolution, precipitation, and clogging processes, which results in reduction of hydraulic conductivity of the aquifer.…”

Influence of the Zeolite ZSM-22 Precursor on a UF-PES Selective Substrate Layer for Salts Rejection

“…The search for effective saltwater fillers and selective nanofiltration (NF) membranes is still growing in interest [1,2]. This is surged by the fast increase in population growth, industrial development, climate change, and other related aspects, which expand the requirement for freshwater and subsequently the need for brackish and saltwater desalination via membrane technologies [3][4][5][6].…”