Quantifying the kinetics-energetics performance tradeoff in bipolar membrane electrodialysis

Bipolar membrane electrodialysis (BMED) is a promising, cost-effective technology for treating highly saline wastewater toward zero-liquid-discharge. Instead of producing low-value minerals of sodium chloride and sulfate, BMED can produce a valuable concentrated acid and base for industrial reuse. In this study, we first develop a numerical model to describe the mass transfer and energy consumption of a BMED process. We then present a systematic framework based on performance tradeoff curves for evaluating the performance of a BMED process that captures the inherent tradeoff between energy efficiency and the kinetic rate of the process. Such a performance tradeoff provides the technical basis for comparison between different BMED operations and systems and for technoeconomic analysis. Using such a framework and Na2SO4 as a model feed solution, we evaluate the impacts of initial feed concentration, target concentration of NaOH, and the ratio between the initial volumes of feed and seed base solutions on the BMED performance. Finally, we also demonstrate that a novel 3D junction bipolar membrane can enhance the performance of the BMED process.