A device for micro-, ultra-, or nanofiltration that includes one or more flat filter modules having flat filter elements arranged in parallel and at a distance from each other and gas injectors of one or more gas lifting systems for producing a circulating cross flow directed tangentially to the surface of the flat filter elements and having at least one rising area, in which the cross flow flows substantially vertically upward, and at least one falling area, in which the cross flow flows substantially vertically downward, in which the rising area flows through 10 to 100% and the falling area flows through 10 to 100% of an inlet-flow volume of the at least one flat filter module.