Performance evaluation of nanofiltration membranes for SWRO brine valorisation: Insights from a pilot plant under real conditions

• NF pilot plant for valorisation of actual SWRO brine in an open research testbed. • Efficient nanofiltration membranes with high rejection and selectivity values. • High-purity of the monovalent-rich stream using NF (98% NaCl) • Key performance analysis at different recovery rates in a NF pilot plant. • Concentrate stream enriched in divalent ions (Mg 2+ , Ca 2+ , SO4. 2− ) The success of a desalination brine valorisation process heavily depends on the effectiveness of the pre-treatment stage, which purifies the brine by reducing the concentration of ions that could form insoluble compounds and hinder system performance. This study focused on testing an innovative nanofiltration (NF) pilot plant operating with 144 m 3 /d of actual brine from an upstream seawater reverse osmosis (SWRO) pilot plant located in the Canary Islands (North Atlantic Ocean). The NF membranes tested (NE8040-40) played a critical role, demonstrating exceptional rejection rates for divalent ions, therefore also increasing their concentration in the divalent-rich stream, setting the stage for future valorisation of the related by-products. Simultaneously, these NF membranes allowed the achievement of a high-purity monovalent-rich stream with Na + and Cl – concentrations reaching approximately 98 %, potentially enabling the generation of valuable commercial products in subsequent stages. The NF system was thoroughly assessed under different conditions of flow, pressure, and recovery rates, incorporating extensive process monitoring with comprehensive sensor data.