Production of high-purity water by continuous electrodeionization with bipolar membranes: Influence of concentrate and protection compartment

Main advantages of continuous electrodeionization with separated beds of cation- and anion-exchange resins and bipolar membranes are compared with other established electrodeionization concepts. Co-ion leakage from the concentrate into the diluate through ion-exchange membranes of limited permselectivity has been identified as the main reason for increased diluate conductivity. Diluate conductivity can be strongly reduced by either a “protection compartment” between the diluate and the concentrate compartment or by a concentrate compartment filled with an ion-exchange resin. In both cases a part of the diluate produced should be used as rinse for the protection or concentrate compartment. Experimental results with two electrodeionization modules comprising either separated beds with protection compartment or concentrate compartment filled with ion-exchange resin are presented and discussed. The influence of the flow rate through the protection compartment, the flow directions in different compartments, the feed water conductivity, the current density as well as the current density distribution on the process performance is investigated.