An innovative beneficial reuse of seawater concentrate using bipolar membrane electrodialysis

Because of the demand for acid solutions in seawater desalination pretreatment and the difficulty of transporting sulfuric acid or hydrochloric acid, seawater concentrate from an RO system was used as the feed for the production of mixed acid by bipolar membrane electrodialysis (BMED) after the removal of calcium ions and magnesium ions. In this experiment, the feasibility of the process was tested using a laboratory ED-cell with an effective area of 88 cm2. Based on the configuration of the BP-C-A-BP, the mixed acid solution was produced in the acid compartment, and the base solution was produced in the base compartment. The results showed that 1 mol/L mixed acid and sodium hydroxide could be produced continuously at a constant current density of 57 mA/cm2 and a flow rate of 0.30 L/h in the continuous-mode BMED. After the production of the acid and base solution, membrane fouling was inspected by measuring the stack resistance and using electron microscopy and surface elemental analysis. No visible fouling deposits on the surface of the CEMs (AEMs) were observed, and there was an increased stack resistance, thus proving that the BMED process for mixed acid production with pretreated RO concentrate is suitable for a long-term run.