| 摘要 |
PROBLEM TO BE SOLVED: To more reliably kill microorganisms existing on or near the surface of a separation membrane by carrying out a water acidifying step in which the pH of water supplied to a membrane separation apparatus is adjusted to a specified value or less while separating and purifying water using the membrane separation apparatus compared with a conventional method in which high concentration sodium hydrogensulfite is added intermittently. SOLUTION: In a membrane separation apparatus, e.g. a reverse osmosis membrane apparatus, a liquid to be treated is supplied to a membrane module under pressure and separated into permeated and concentrated liquids so as to carry out the production of fresh water, concentration or separation. The membrane can reliably be sterilized by setting the pH at <=4 and the sterilization is effectively applied to membrane filtration using seawater as water to be supplied. An acid is ordinarily used for pH adjustment and sulfuric acid is preferably used because it is economical. In order to attain <=ph 4, >=120 ppm sulfuric acid is preferably added. Sulfuric acid is preferably added for 0.5-2.5 hr at intervals of 1 day, 1 week o 1 month.
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