| 摘要 |
PROBLEM TO BE SOLVED: To provide a separation method capable of more stably obtaining a low concentration solution from a high concentration solution in high yield, with less energy, at a lower cost and with high efficiency. SOLUTION: In the reverse osmosis separation method of sea water or salt water by which reverse osmosis membrane module units arranged at multi-stages are used and concentrated water in a reverse osmosis membrane module unit at a front stage is raised in pressure and fed to a reverse osmosis membrane module unit at the subsequent stage and treated, the reverse osmosis membrane module units arranged at multi-stages are operated such that operational pressure P (n) of the reverse osmosis membrane module at the (n)th stage and the operational pressure P(n+1) at the (n+1)th stage are in the range of the following equation ; 1.15<=P(n+1)/P(n)<=1.8.
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