Batch mode and continuous desalination of water using flowing carbon deionization (FCDI) technology

•Continuous membrane capacitive deionization process•90% water recovery and > 99% desalination rate•Unprecedented salt adsorption capacity of 260 mg NaCl/g carbon

We report batch and continuous electrochemical desalination utilizing the ion adsorption capacity of a slurry containing carbon particles. Two carbon suspensions and the feed water are fed into the electrochemical cell operated according to the principle of membrane assisted capacitive deionization (MCDI). In a batch mode operation after the desalination step is complete the adsorbed ions are discharged from flowing electrodes to the same portion of water using polarity reversal. Operation with 15 g NaCl/l water solution resulted in extremely high apparent salt adsorption capacity (SAC) value of 260 mg/gdry carbon. This value is much higher than the highest value of SAC reported until now — 14.3 mg/g. The reason for this phenomenon is not clear and further research is currently performed. In a new truly continuous process, both slurry streams are continuously recirculated between the desalination module and a regeneration/concentration module operated with the same functionality but with reversed potential. Ions desorb from the flowing electrodes and concentrate through the membranes into a purge stream. We prove continuous operation with desalination rate of more than 99% for an initial salt concentration of 1 g NaCl/l. Concentration factors depend on the recovery, with 90% water recovery being demonstrated easily.

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