To provide an operational method of a
reverse osmosis membrane device for improving
water quality of treatment water of a
reverse osmosis membrane device, especially,
boron removal rate, in treating
treated water with the
reverse osmosis membrane device by adjusting pH.SOLUTION: A first reverse
osmosis membrane device 1, a second reverse
osmosis membrane device 2, and a water sending channel 3 are included. A water sending channel 4 of treatment water W2 and an exhaust channel 5 of concentrated water W3 are respectively connected to the second reverse
osmosis membrane device 2. Also, a NaOH
aqueous solution supply source 6 is connected to the water sending channel 3. Moreover, first
pH measurement means 11 for measuring pH of
treated water W1 is provided, and second
pH measurement means 12 for measuring pH of the concentrated water W3 is provided. pH of the
treated water W1 of the second reverse osmosis membrane device 2 is measured by the first
pH measurement means 11, and pH of the concentrated water W3 of the second reverse osmosis membrane device 2 is measured by the second pH measurement means 12, and an addition amount of NaOH
aqueous solution from the NaOH
aqueous solution supply source 6 is controlled so as to have a relation of: pH of supply water W1≤pH of the concentrated water W3.SELECTED DRAWING: Figure 1