A pilot plant investigation on a real seawater brine valorisation via electrodialysis with bipolar membranes

Environmental concerns related to industrial wastewater streams can be minimized by employing zero/minimum liquid discharge strategies, recovering high-value materials to make them economically competitive. However, selective recovery of minerals requires suitable reactants, such as acid and alkaline solutions. To this aim, Electrodialysis with Bipolar Membranes (EDBM) can be employed to in-situ produce chemicals. This work studies a semi-industrial scale EDBM unit, fed by either a real seawater brine or a synthetic NaCl solution. Risk mitigation approaches adopted to guarantee continuous operation are described. EDBM performance, as operating conditions vary, is evaluated under two control strategies (i.e., flowrate and pressure control). The pressure control strategy guarantees higher performance, minimizing undesired convective fluxes. Values of current efficiency and specific energy consumption of 68 % and 2.4 kWh kg−1, respectively, were obtained for the alkaline product at 1.1 mol L−1 concentration. Multi-ion transport within membranes is evaluated under pressure control strategy. The analysis highlights a dominant passage of Cl−1 and Na+ in the acid and alkaline stream, respectively, resulting in products containing >90 % of Cl−1 (acid stream) and > 98 % of Na+ (alkaline stream). These results proved the attractiveness of the EDBM process in treating real brine to produce acid and alkaline solutions.