Return flow ion concentration polarization desalination: A new way to enhance electromembrane desalination

In electromembrane desalination processes such as electrodialysis (ED) and ion concentration polarization (ICP) desalination, ion-depleted boundary layers constitute the desalted, product stream, yet also cause high resistivity and voltage drop. Directly manipulating fluid flow streams is a new method to break this fundamental trade-off for electromembrane desalination. In this work, we are introducing a novel electromembrane desalination architecture that allows a feed stream to return to the feed inlet side of the membrane (hereby named as return-flow (RF) architecture) to improve the energy efficiency by re-distributing and controlling the depleted boundary layer, even at high current values. The technical feasibility of this idea was examined in ICP desalination process (RF-ICP) with a wide range of feed salinity from 10 to 70 g/L. For a partial desalination, RF-ICP (similar to 75 cm(2) of membrane area) has achieved similar power consumption compared to batch-ED with 3 times bigger membrane area (200 cm(2)) with a higher area efficiency for salt removal, which translates into lower optimal desalination cost. The techno-economic analysis of RF-ICP have been performed for the treatment of 70 g/L brine waste. For partial desalination of 70 brine down to 35 g/L, RF-ICP desalination achieved overall water cost as low as $2.57/m(3) ($0.41/barrel). This could translate into reduction in total water cost up to 31% for zero brine release scenarios, depending on the concentrated brine treatment cost. These results show that return flow architecture can improve the performance of electromembrane desalination, enabling more flexible water treatment for many real-world applications. (C) 2019 Elsevier Ltd. All rights reserved.