Operation-driven stabilization of batch bipolar membrane electrodialysis for NaOH regeneration from SWRO brine

Batch bipolar membrane electrodialysis (BMED) is a promising approach for NaOH regeneration from saline streams; however, its performance often deteriorates during operation. Performance deterioration can arise from multiple factors, including membrane fouling, scaling, and operation-driven changes in solution properties; however, its behavior under realistic brine conditions remains insufficiently understood. In this study, we found that performance deterioration in batch BMED was associated with operation-driven evolution of the electrochemical environment during batch operation. Under realistic brine conditions, continuous changes in solution properties were accompanied by sustained current decay and reduced NaOH production. To address this limitation, an operation-driven control framework was developed, combining passive control through solution volume configuration and active regulation using threshold-based operation. Passive control delayed the onset of performance deterioration, while active control stabilized system behavior by dynamically regulating the electrochemical environment. As a result, NaOH concentration increased from 0.63 M to 1.75 M, accompanied by improved current efficiency (~60%) and reduced specific energy consumption (~2.6 kWh kg −1 NaOH). The strategy also enabled high NaOH concentration (3.14 M) under high-salinity brine, demonstrating its robustness. These findings highlight the importance of operation-driven control for achieving stable and efficient NaOH regeneration in batch BMED. • Performance decay in batch BMED is driven by conductivity evolution • Passive volume control delays but does not prevent deterioration • Active conductivity regulation stabilizes electrochemical conditions • Operation-driven control improves efficiency and reduces energy use • Up to 1.7 M NaOH achieved with ~60% current efficiency