DESALTING APPARATUS

PROBLEM TO BE SOLVED: To reduce the deterioration of ion exchange membranes in a deionization apparatus by installing an ion exchange means filled with a weakly acidic cation exchange resin in a circulation line for refluxing condensed water discharged from a deionization apparatus. SOLUTION: City water is desalted by a desalting apparatus equipped with a reverse osmosis device 1 and electric deionization devices 2, 6. Condensed water from the condensation chambers of the deionization devices 2, 6 is pumped by transfer pumps 4, 7 to reflux it to the inlets of the chambers. An ion exchange apparatus 3 filled with a weakly acidic cation exchange resin is installed in one circulation line to prevent scale generation in the ion exchange membranes of the deionization devices 2, 6. When the conductivity of treated water in the devices 2, 6 has exceeded a prescribed value, the ion exchange membranes are washed by passing a strong acid solution. At a time point when the hardness of treated water in the ion exchange apparatus 3 has exceeded a prescribed value, the regeneration of the weakly acidic cation exchange resin is performed.