Improving the energy utilization efficiency of flow electrode capacitive deionization (FCDI) with multiple series flow electrodes.

[Display omitted] • The series connection method of flow electrode ST-SC and MT-SC in multi-stage FCDI were proposed. • Flexible current control each level device to decrease ENRS. • MT-SC operating mode was more energy-efficient and efficient than traditional single stage devices. • The MT-SC operating mode could fully utilize the energy released during the desorption process. This article proposed a three-stage flow electrode capacitive deionization (FCDI) device, in which the flow electrodes were connected in series and circulated among the three stages. Four different methods of flow electrode series connection (ICC, SCC, ST-SC, and MT-SC) were investigated. The results showed that the MT-SC mode achieved the best desalination performance and saved 43.47 % of energy. To further reduce energy consumption, the current of the three-stage device was further optimized using flexible current, and the mode with gradually decreasing current (15 mA-10 mA-5 mA) was the most effective. Moreover, the effects of flow rate, influent salt concentration and current on the desalination performance of the three-stage FCDI device were studied. A fair comparison was made between the desalination performance of three-stage and single-stage FCDI devices, and the results showed that the multi-stage FCDI device with series flow electrodes can fully utilize the energy released during the short-circuit desorption process to reduce the energy consumption of desalination. Therefore, the multi-stage FCDI devices were more energy-efficient and economical than traditional single-stage devices. [ABSTRACT FROM AUTHOR]