Integration of nanofiltration, ion exchange, and electrodialysis with bipolar membranes for the valorisation of brines: From seawater desalination plants to on-site chemicals production facilities

Abstract

Water scarcity is a growing concern due to population growth, climate change, pollution, and inadequate water management. Innovative approaches are necessary to secure a reliable water supply to address this challenge. Seawater desalination has emerged as a promising option to supplement freshwater resources, but its by-product (i.e., salt-concentrated brine) poses a significant environmental threat. Current disposal methods include direct disposal, evaporation ponds, and, in specific cases, land application in irrigation for low-salinity brines, but these practices have negative environmental consequences. As a result, alternative strategies for brine management directed to materials circularity by process integration are being developed. Integration of membrane technologies, such as Nanofiltration, has shown promising efficiency for improving pre-concentration, while Electrodialysis with bipolar membranes (EDBM) can transform brines into chemicals. Additionally, Ion Exchange processes could be used as a polishing stage to ensure the safe operation of EDBM by reducing the levels of divalent cations responsible for membrane scaling. This study proposes integrating three technologies and assesses their feasibility by conducting a techno-economic analysis using previously developed simulation tools. Results suggest that the proposed technologies integration can be a promising alternative of Minimum Liquid Discharge system to treat desalination brines, while producing high-purity chemicals. Finally, the economic results demonstrated a minimum total Levelized Cost of NaOH of 344 €/tonNaOH. This indicates that the system proposed in this study is cost-effective and competitive with current market supplies.