| 摘要 |
PROBLEM TO BE SOLVED: To facilitate the pH control of water to be treated, to reduce apparatus cost and running cost and to prevent the discharge of carbon dioxide to the atmosphere in a pH control method of water for adding a slaked lime aqueous solution to water to be treated to raise the pH of water to be treated and subsequently adding carbonic acid to water to be treated to lower the pH thereof. SOLUTION: Carbonic acid is added to water to be treated by directly dissolving carbon dioxide in water to be treated through a gas permeable membrane. For example, carbon dioxide in a carbon dioxide cylinder 44 is introduced into a carbon dioxide dissolving apparatus using a gas permeable membrane through a carbon dioxide introducing pipe 46 and dissolved in the water to be treated in a carbon dioxide dissolving tank 40 through the gas permeable membrane by the carbon dioxide dissolving device 50.
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