| 摘要 |
PROBLEM TO BE SOLVED: To provide a two-stage reverse osmosis treatment apparatus and method capable of stably and inexpensively obtaining treated water of excellent quality without requiring an expensive and exclusive alkali addition amount controller. SOLUTION: In a two-stage reverse osmosis membrane treatment apparatus equipped with a first stage reverse osmosis membrane treatment apparatus for treating raw water to obtain primary transmitted water, an alkali addition means for adding alkali to primary transmitted water and a second stage reverse osmosis membrane treatment apparatus for treating supplied primary transmitted water to obtain secondary transmitted water, a membrane having a region, where the fluctuation of the electric resistivity of secondary transmitted water to the fluctuation ofΔpH±0.5 becomes±0.2 MΩ.cm or less within a pH range of 7-9 when the electric conductivity of the supply water to the second reverse osmosis membrane treatment apparatus is 5μS/cm and the concentration of free carbonate thereof is 5 mg CaCO3/L is used as the reverse osmosis membrane of the second stage reverse osmosis membrane treatment apparatus. A method for adding a constant amount of alkali in this apparatus is provided.
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