| 摘要 |
PROBLEM TO BE SOLVED: To obtain high quality water high water recovery ratio by subjecting concentrated water of the first of RO devices (reverse osmosis membrane separators) arranged in series to RO treatment by an RO device separately placed, and subjecting the permeated water to deaeration treatment together with the concentrated water in order by the RO devices arranged in series to make the treated water be feed water to the first RO device. SOLUTION: After raw water is subjected to pretreatment such as flocculation and sedimentation, membrane filtration, and active carbon treatment as the need arises, acid is added to it to form the solute into CO2 which is easily removed by a deaerator 2. In the deaerator 2, CO2 in the raw water is changed to a gaseous phase to remove it. In three-stage RO treatment, after the concentrated water of a first RO device 3 is subjected to RO treatment by a fourth RO device 6 and the obtained permeated water is subjected to deaeration treatment together with the concentrated water of second and third RO devices 4, 5 by a deaerator 7, the deaerated water is reused as feed water to the first RO device 3. By returning the permeated water obtained by subjecting the concentrated water of the first RO device 3 to RO treatment and the concentrated water of the second and third RO devices 4, 5 to reuse them, water recovery is sharply increased.
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