Patent ID: 7520971

Claim:
An electrodeionization apparatus comprising: a cathode; an anode; concentrating compartments into which concentrated water is introduced; desalting compartments for desalting water, said concentrating compartments and desalting compartments being alternately formed by arranging a plurality of cation exchange membranes and a plurality of anion exchange membranes alternately between the cathode and the anode, each of the desalting compartments having an upper stream zone and a lower stream zone; and ion exchange resins filled in the desalting compartments, said ion exchange resins comprising an anion exchange resin and a cation exchange resin, said anion exchange resin and cation exchange resin being completely mixed together throughout each of the desalting compartments, wherein when a mixing ratio of the anion exchange resin to a total amount of the anion exchange resin and the cation exchange resin is expressed as A volume % at the upper stream zone in each of the desalting compartment and expressed as B volume % at the lower stream zone in each of the desalting compartment, A is 66 to 80 and B is 50 to 65; or A is 55 to 65 and B is 66 to 80.