Abstract: In a method of filtration, a liquid to be filtered is brought into contact with the surface of a filter medium and is passed through the filter medium. A supernatant liquid layer is created on the surface of the filter medium, and the upper level of the liquid layer is suitably controlled. A hydraulic path is organized in the liquid layer, and a stream of the liquid to be treated is brought to the inlet of the hydraulic path. Liquid that has passed through the filter medium is recovered for n cycles by reinjecting the liquid into the supernatant layer at the outlet of the hydraulic path, producing in a section of the path a meeting of two opposed streams. The treated liquid is then drawn off after n cycles.