Coupling of electromembrane processes with reverse osmosis for seawater desalination: Pilot plant demonstration and testing

Abstract

Reverse osmosis (RO) is the most widespread technology to produce drinking water from seawater (SW). However, the integration of different membrane processes offers interesting alternatives. In this work, electromembrane processes were integrated with RO to desalinate real seawater in a pilot plant with 25 m3/day capacity. Electrodialysis (ED, either two-stage or single stage), shortcut reverse electrodialysis (scRED) and assisted reverse electrodialysis (ARED) pre-desalinated seawater before RO with the ED-ED-RO, ED-RO, and scRED-ARED-RO process schemes. Treated wastewater was used as salt sink in the scRED-ARED tests. The performance of the pilot plant can be summarized as follows: water recovery of ~27–51%, productivity of ~7–14 L/(m2 h) in the electromembrane processes and of ⁓19–31 L/(m2 h) in the RO process, energy consumption of 3.5–8.4 kWh/m3. The ED-RO configuration yielded the maximum productivity of the electromembrane step, while the scRED-ARED-RO integration reached the minimum energy consumption. Overall, the energy performance of the pilot plant (especially in the ED-RO and scRED-ARED-RO schemes) was comparable to that of a standalone SWRO system. The field tests demonstrated that the coupling of electromembrane processes with RO is feasible and suggest the possibility to develop alternative and competitive industrial pants for seawater desalination.