Improvement in the desalination performance of membrane capacitive deionization with a bipolar electrode via an energy recovery process

In the practical implementation of capacitive deionization (CDI), membrane CDI with a bipolar electrode (bipolar MCDI) is emerging as one of the alternative CDI platforms due to its favorable cell configuration for scale-up and low current originating from the serial connection of electrodes. Nevertheless, one obstacle to practical use is that there are few studies about the energy recovery process for the high energy efficiency of bipolar MCDI, requiring further research. Therefore, in this study, we propose a bipolar MCDI process with energy recovery and assess its potential by analysis of a lab-scale module with a single stack and nine stacks of the bipolar electrode (i.e., 2.4 V and 12 V system, respectively) and a pilot-scale module with 250 stacks (i.e., 300 V system). As a result, the energy consumption of the bipolar MCDI systems was reduced by 43% and 41% in the lab-scale modules with 2.4 V and 12 V systems, respectively, via energy recovery. Furthermore, the energy recovery led to a 40% reduction in the energy consumption of bipolar MCDI, even in the pilot-scale modules of the 300 V system. The results suggest that energy recovery in bipolar MCDI can be one of the essential processes and it has a strong potential for implementation in real industrial and environmental applications.