MULTISTAGE SEPARATION SYSTEM USING REVERSE OSMOSIS MEMBRANE

摘要

A separation system for obtaining a low concentration solution with high quality stably from a high concentration solution at high recovery ratio is provided to obtain a constant and stable recovery ratio by controlling a module recovery ratio within vessels of respective stages to an allowable limit value or less, and improve efficiency and reduce cost even without an additional device such as a booster pump by disposing reverse osmosis membranes with different separation performance on respective stages. In a separation system comprising a plurality of vessels in which plural membrane modules are installed in parallel to form a stage, and at least two stages gathered to be arranged in series, a multistage separation system using the reverse osmosis membranes is characterized in that the reverse osmosis membranes are disposed in such a combination that a reverse osmosis membrane mounted on a rear stage(4) of the separation system has a 25 to 250% higher specific permeate flux than a reverse osmosis membrane mounted on a front stage(3) of the separation system. Each of the membrane modules has a recovery ratio of 15% or less. The separation system comprises two or more stages, and the number of the vessels in the rear stage is 1/4 to 3/4 of that of the vessels in the front stage. The membrane modules are spiral-wound type modules.