PURPOSE: To reduce the pressure loss of both the piping for discharging treated liquid and the piping for back-washing without enlarging the diameter of pipe for both pipings and to carry out a speedy back-washing by providing the vent piping for back-washing liquid to the upper part of a hermetic vessel provided with hanging hollow thread membrane filter modules.
CONSTITUTION: The vent piping 54 for back-washing is provided to the upper part of the hermetic vessel 31 of an outer pressure type hollow thread membrane filter device. When the back-washing is carried out, the supply of the liquid to be treated from a piping 36 for supplying the liquid to be treated is stopped, and the outlet valve 45 of the piping 44 for discharging the treated liquid is closed. Then, a stop valve 55 is opened to discharge the treated liquid 46 filling the upper part than the open part 54a of the piping 54 and the inside of the piping 44 and the air piping 47 for back-washing. In this state, when the stop valve 55 is closed, a stop valve 51a of the vent piping 51 is opened, a stop valve 52a is closed, and a stop valve 49 is opened to supply compressed air to the air piping 47 for back-washing, then, the treated liquid 46 is instantly pressurized and the impurities stuck to the outer surface of the thread membrane are exfoliated and washed out.
KATO MOTOI
WATANABE MASARU
