Production of high purity water using membrane-free electrodeionization with improved resin layer structure

A novel membrane-free electrodeionization (MFEDI) process has been proposed and tested successfully for high purity water production in our previous work. However, to prevent the ions backward migration, the electrode polarity had to be reversed during regeneration, which complicated the regeneration process, reduced the regeneration efficiency and shortened the electrode life. In order to avoid the electrode polarity reversal and enhance the regeneration efficiency, the resin layer structure and the types of mixed resins were changed in this work to form a MFEDI without electrode polarity reversal which was then tested by desalinating the synthetic two-pass RO permeate of seawater with a total of 40 operational cycles. Results demonstrated that the backward migration of Na+ ions was prevented effectively; the weak-type resins facilitated the water dissociation and promoted the regeneration of strong-type resins significantly. Both good purification and effective regeneration were achieved. The conductivity of effluent was 0.060-0.063 μS/cm only. The energy consumption and the water recovery were 0.24 kW h/m3 water and 96.1%, respectively. Repetitive experimental results showed this MFEDI system could work stably.