| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing freshwater having the quality of drinking water from salt water in high efficiency and at a high recovery rate. SOLUTION: The method for producing freshwater from salt water by using a freshwater production apparatus provided with nanofiltration membrane units arranged in series in two or more stages and a desalination unit comprises the steps of: warming the salt water to be supplied to the first-stage nanofiltration membrane unit by using a heating unit; making the warmed salt water pass through the first-stage nanofiltration membrane unit; making the nanofiltrate from the first-stage nanofiltration membrane unit pass through the second-stage nanofiltration membrane unit; making the salt-concentrated water from the second-stage nanofiltration membrane unit or the succeeding unit pass through the desalination unit to produce desalted water; and mixing the desalted water with the nanofiltrate from the second-stage nanofiltration membrane unit or the succeeding unit to produce freshwater. COPYRIGHT: (C)2008,JPO&INPIT
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