Sustainable off-grid hybrid desalination with zero brine discharge for water and salt recovery

This work presents the design and analysis of an off-grid zero brine discharge (ZBD) hybrid desalination system for simultaneous water and salt recovery. The system integrates reverse osmosis, electrodialysis, and crystallization technologies to optimally exploit their complementary advantages under variable operating conditions and is fully powered by renewable energy, ensuring sustainable operation based on green electricity. Seawater is first treated by reverse osmosis (RO) to achieve high water recovery. The resulting brine is then processed in an electrodialysis stage, producing two streams: a high-salinity stream sent to a crystallizer and a low-salinity stream, close to seawater concentration, safely discharged to the sea. A final crystallization step enables additional freshwater recovery and the complete elimination of brine discharge through solid salt production. A combined cost and thermodynamic assessment is performed within a simultaneous optimization framework, in which all design and operating decisions are optimized concurrently. This approach minimizes the risk of overlooking high-quality feasible solutions that are difficult to identify using sequential or heuristic methods. The results indicate that the hybrid configuration significantly improves water recovery compared to standalone technologies while minimizing environmental impact. The proposed system provides a fully sustainable desalination solution for remote and water-scarce regions.