a removal system for membranes in a membrane filtration system of the type where the membranes are supported on a membrane support rack in a tank or vessel which , in use , contains liquid to be filtered . the tank comprises a selectively operable opening which in an open position allows the removal of the membranes from the tank . the membrane support rack is movable relative to the tank to move said membranes through the opening , in its open position , to a position outside the tank .