Patent ID: 7276171

Claim:
A method for cleaning a separation membrane of an out-of-basin type for filtering tank water with circulation, the method comprising the steps of: connecting the separation membrane to a biological treatment tank through a circulation passageway; connecting the separation membrane to a waste sludge line having a discharge location separate from the biological treatment tank, returning at least a portion of backwash drain containing sludge peeled from a surface of the separation membrane to the biological treatment tank through one of a backwash drain passageway and a circulation passageway in a backwash process with water; peeling the sludge from the surface of the separation membrane by a backwash with water to discharge the sludge out of a membrane module containing the separation membrane; cleaning the surface of the separation membrane with chemicals after the backwash with water; and discharging the chemicals and sludge removed by the chemicals through the waste sludge line to the discharge location separate from the biological treatment tank such that the chemicals are not introduced into the biological treatment tank.