PURPOSE: To enhance washing effect and to enable the repeated use of a chemical solution while inexpensively performing the washing of a membrane with good efficiency, by contacting the chemical solution with the membrane in a state divided into plural times and reusing the chemical solution used in washing on and after a second stage without treating the same.
CONSTITUTION: (n) Chemical solution tanks 11W13 are provided in order to wash a membrane in a multistage fashion. At first, an all amount of the chemical solution such as a NaOH solution of the chemical solution tank 11 is supplied to a washing tank 3. The chemical solution is sent to the concn. chamber 1a of a membrane separation apparatus 1 through piping 5 and returned to the washing tank 3 through piping 40. The solution transmitted through the membrane 2 is guided to an activated carbon filter tower 6 through pipings 50, 50a and purified to be introduced into a recovery chemical solution tank 21 from piping 51. After first stage washing, air is passed through the pipings 5, 40 to send the contents therein to the washing tank 3 and subsequently withdrawn to a concentrate tank. In second stage washing, the chemical solution of the chemical solution tank 12 is transferred to the washing tank 3 and sent to the concn. chamber 1a before returned to the washing tank 3. The solution transmitted through the membrane 2 is introduced into the recovery chemical solution tank 22 from pipings 50, 52. This operation is successively repeated.
FURUICHI MITSUHARU
ICHIYANAGI NAOTO
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