Power-free bipolar membrane electrodialysis for acid-alkali production in river estuaries

Recent studies suggest that 2–2.6 TW blue energy can be harvested by mixing coastal seawater with freshwater world widely, but the extractable part was limited due to undesired development of conversion techniques. In this study, a novel power-free bipolar membrane electrodialysis process is proposed for the closed-loop utilization of salinity gradient energy and the salt resources in seawater. The system was evaluated using theoretical and experimental methods. Significance of the various membrane modules and operational conditions was evaluated. Based on fluid dynamics simulations and fluid online imaging technologies, a prototype electro-membrane reactor was fabricated to maximize the achievable energy and acid/base products. The acid production rate reached 6.9 mmol h−1 when feeding simulated seawater (30 g/L NaCl) and river water (1 g/L NaCl). The protocols provided in this work offer an effective route for developing advanced membrane processes for the harvesting of salinity gradient energy and acid-alkali production.