Abstract: A method of backwashing a membrane filtration module (4), said module (4) including one or more membranes (5) located in a feed-containing vessel (3), the membranes (5) having a permeable wall which is subjected to a filtration operation wherein feed containing contaminant matter is applied to one side of the membrane wall and filtrate is withdrawn from the other side of the membrane wall, the method including: removing liquid from the feed-containing vessel (3) until the level of liquid in the feed-containing vessel (3) falls to a first level (L2) below an upper level of the membranes; suspending the filtration operation; performing a liquid backwash of the membrane wall until liquid level within the feed-containing vessel (3) rises to a second predetermined level (L1) above said first level; aerating the membrane surface with gas bubbles to dislodge fouling materials therefrom; performing a sweep or drain down of the feed-containing vessel (3) to remove the liquid containing the dislodged contaminant matter

Abstract: A method and apparatus for backwashing a membrane filtration system wherein permeate remaining present in the filtration system wherein permeate remaining present in the filtration system when the filtration process is stopped or suspended is used to provide liquid for backwashing the membrane pores during a backwashing process.

Abstract: A method and filtration module (5) for providing gas bubbles within an array of vertically disposed porous hollow membranes (6) to clean the outer surfaces of said membranes (6) when the array is immersed in a liquid by feeding (10) the gas bubbles into the array transversely of the vertical axis of the array. In one preferred form, the gas bubbles are retained within the array using a sleeve (11) surrounding the array (6) at least along part of its length.