Synergistic optimization of membrane distillation-reverse electrodialysis for sustainable desalination and salinity gradient power generation

Water desalination, dominated by seawater reverse osmosis, presents issues such as low water recovery (∼50 %), brine management challenges, and high energy consumption. In this study, an optimized strategy integrating membrane distillation (MD) and reverse electrodialysis (RED) is proposed to reduce the energy demands and environmental footprint of MD brine. Extensive lab-scale experiments on MD and RED demonstrated a novel parametric optimization of feed concentrations, temperatures, and flow conditions to maximize water recovery and energy output. The MD design achieved a maximum flux of 27 L per square meter per hour (LMH), enhancing water recovery by up to 80 %. The RED stack reached an open circuit voltage of 0.55 V and a maximum power density of 0.47 W/m² at 60 °C and 5 M MD brine concentration. The study emphasizes the process intensification achieved through the integration of MD and RED, where synergistic interactions between desalination and energy recovery significantly enhance system efficiency. Moreover, specific thermal energy consumption calculations indicate that using low-grade waste heat is synergistic with process intensification and aligns with the circular economy paradigm.