Patent ID: 8641904

Claim:
A method for backwashing a filtration membrane comprising the steps of: housing a filtration element within a casing, said filtrate element being formed of a ceramic filtration membrane comprising a substrate layer defining a secondary side of the ceramic filtration membrane and a separation layer formed on said substrate layer and defining a primary side of the ceramic filtration membrane; supplying raw water to the primary side of the ceramic filtration membrane and filtering the raw water to form filtrate water, which is removed from the casing via a filtrate water feed pipe and a filtrate water header pipe, wherein the filtrate water header pipe is arranged on a lower side of the filtrate water feed pipe; and supplying backwashing air to the ceramic filtration membrane via the filtrate water feed pipe when the ceramic filtration membrane is clogged with an obstructing material formed from filtering the raw water, wherein the backwashing air is supplied in the following stages: supplying backwashing air controlled to a pressure not exceeding a bubble point of the substrate layer from the filtrate water feed pipe to the secondary side of the ceramic filtration membrane to gradually push out filtrate water that is built-up within the ceramic filtration membrane to the primary side of the ceramic filtration membrane, and discharging the built-up filtrate water from a lower header pipe connected to the casing; increasing a pressure of the backwashing air to a controlled pressure exceeding the bubble pressure of the substrate layer but not exceeding a bubble pressure of the separation layer from the filtrate water feed pipe to the secondary side of the ceramic filtration membrane to gradually push out filtrate water that is built-up in the separation layer to the primary side of the ceramic filtration membrane, and discharging the built-up filtrate water from the lower header pipe connected to the casing; and increasing a pressure of the backwashing air to a controlled pressure exceeding the bubble pressure of the separation layer from the filtrate water feed pipe to the secondary side of the ceramic filtration membrane to peel off the obstructing material from the primary side of the ceramic filtration membrane with the backwashing air.