| 摘要 |
PROBLEM TO BE SOLVED: To efficiently and more inexpensively obtain a solution of a low concentration from a solution of a high concentration with less energy is a high yield by providing a means for adjusting a pressure of a permeated water or a flow rate of a permeated water at least single stage of a reverse osmosis membrane module unit arranged at multi-stages. SOLUTION: A supply liquid (a seawater)6 is pressurized at about 9.0 MPa by a booster pump 1, supplied to a reverse osmosis membrane module unit 2 on the first stage, and the supply liquid 6 is separated into a permeated liquid 3 of a low concentration permeated a membrane, and a concentration liquid 4 of a high concentration which does not permeate the membrane. Herein, a pressure of the permeated water is adjusted to a pressure of the supply liquid by a permeated water pressure adjusting valve 7. When, for example, a pressure of about 4.4 MPa is applied to the permeated water side, an effective pressure of subtracting an osmotic pressure and the permeated water pressure from the supply liquid pressure is suppressed to about 2.0 MPa, and a fouling can be prevented. The supply water in the reverse osmosis membrane module unit 10 on the second stage is concentrated, and an amount of the permeated water can be also sufficiently obtained while the fouling is prevented because the permeated pressure becomes high.
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