Patent ID: 7083730

Claim:
A method of producing purified water and sodium chloride from salt water that contains sodium chloride, the method comprising: feeding the salt water to a reverse osmosis unit; operating the reverse osmosis unit to separate the salt water into a permeate of purified water which is recovered and a retentate that contains sodium chloride that is concentrated with reference to the salt water; feeding the retentate to an electrodialysis unit having a plurality of membranes, wherein at least one electrodialysis membrane is a univalent anion-selective membrane and at least one other electrodialysis membrane is a univalent cation-selective membrane; operating the electrodialysis unit to separate the retentate into a diluate that is depleted in sodium chloride with reference to the retentate, and a concentrate that is concentrated in sodium chloride with reference to the retentate, wherein at least a portion of the diluate is recycled back to the feed to the reverse osmosis unit; feeding the concentrate to a salt-recovery unit; and operating the salt-recovery unit to recover sodium chloride from the concentrate.