Abstract: An apparatus for producing deionized water, comprising an electrodialyzer having cation exchange membranes and anion exchange membranes alternately arranged to form demineralizing compartments and concentrating compartments and having ion exchangers accommodated in the demineralizing compartments, and designed to conduct an electric current while supplying water to be treated to the demineralizing compartments, wherein a spacer is arranged in each concentrating compartment to maintain the thickness of the concentrating compartment, and the cation exchange membranes or the anion exchange membranes are incorporated in their dry state in the electrodialyzer, whereby water is supplied to the electrodialyzer, while each ion exchange membrane is brought in contact with the spacer by a pressure from the demineralizing compartment side.

Abstract: An apparatus for producing deionized water consisting essentially of an electrodialyzer having cation exchange membranes and anion exchange membranes alternately arranged between a cathode and an anode to form demineralizing compartments and concentrating compartments, and ion exchangers accommodated in the demineralizing compartments, wherein a pressure of from 0.1 to 20 kg/cm2 is exerted between the ion exchangers accommodated in the demineralizing compartments and the cation exchange membranes and anion exchange membranes defining the demineralizing compartments.

Abstract: An apparatus for producing deionized water comprising an electrodialyzer having cation exchange membranes and anion exchange membranes alternately arranged between a cathode and an anode to form demineralizing compartments and concentrating compartments, and ion exchange resin particles packed in the demineralizing compartments, wherein the ion exchange resin particles are a mixture of at least two groups of ion exchange resin particles having a particle size distribution such that particles having particle sizes of from 75 to 125% of the average particle size, are at least 85 wt % of the total amount, and the average particle size of a group of ion exchange resin particles having the maximum average particle size, is at least 1.5 times the average particle size of a group of ion exchange resin particles having the minimum average particle size.

Abstract: An apparatus for producing deionized water consisting essentially of an electrodialyzer having cation exchange membranes and anion exchange membranes alternately arranged between a cathode and an anode to form demineralizing compartments and concentrating compartments, and ion exchangers accommodated in the demineralizing compartments, wherein a pressure of from 0.1 to 20 kg/cm.sup.2 is exerted between the ion exchangers accommodated in the demineralizing compartments and the cation exchange membranes and anion exchange membranes defining the demineralizing compartments.

Abstract: A method for producing deionized water by self-regenerating type electrodialysis deionization, which comprises (i) using a deionized water-producing apparatus containing an electrodialyzer comprising cation exchange membranes and anion exchange membranes alternately arranged between an anode compartment provided with an anode and a cathode compartment provided with a cathode, demineralizing compartments compartmentalized with anion exchange membranes on the anode side and compartmentalized with cation exchange membranes on the cathode side, and concentrating compartments compartmentalized with cation exchange membranes on the anode side and compartmentalized with anion exchange membranes on the cathode side, the electrodialyzer having ion exchangers accommodated in the demineralizing compartments, and (ii) applying a voltage while supplying water to be treated to the demineralizing compartments to remove impurity ions in the water to be treated, wherein at least a part of the untreated water or already treate