| 摘要 |
PROBLEM TO BE SOLVED: To suppress adhesion of slim to a membrane and prevent deterioration of the membrane by an oxidizing agent by adding silver ion and a reducing agent. SOLUTION: In order to carry out membrane separation treatment by supplying raw water to a reverse osmosis membrane module by a raw water pump P1, a reagent containing Ag<+> and a reducing agent is injected into a reagent tank 1 by a reagent pump P2. As a Ag<+> source, water-soluble silver salts such as AgNO3 , AgSO4 , AgCl, etc., may be used and among them, AgNO3 is preferable in a view point of solubility. NaHSO3 may be used as the reducing agent. In this membrane separation method, it is preferable to use a separation membrane protective reagent, in which an Ag salt and the reducing agent are integrated, and the water soluble silver salt such as AgNO3 is so added as to be 1-50μg/l of Ag<+> concentration in raw water and at the same time the reducing agent such as NaHSO3 is so added as to be equal to or more than the residual chlorine in the raw water in mole concentration.
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