Abstract: The invention relates to a method for washing a filter intended for cleansing a contaminated liquid and having a granular bed, a drainage system located beneath the bed, means for introducing first and second liquid flows into the bed, wherein the first liquid flow is operative to fluidize solely upper bed layers at least locally, and the second liquid flow is operative to fluidize the bed throughout the whole of its depth. The method teaches ejecting the flows of liquid selectively into the bed through orifices which are placed in the bed at a location between the highest point and the lowest point therein and which are substantially equidistant from the upper surface of the bed; and by introducing the first liquid stream into the upper layers of said bed in a smaller quantity and at a corresponding smaller rate than the second liquid stream, such that the bed layers located beneath these upper layers will be unaffected by the ongoing bed washing operation.

Abstract: The present invention relates to a filter provided with a filter bed consisting of a granular material, which does not comprise layers of coarser material. In the filter bed at least one liquid distributor is arranged which defines an expansion space otherwise defined by areas of repose for the bed material, in which space at least one outflow opens above the areas of repose. The distributor is so designed, that the liquid can flow out of the openings with great energy and fill the cavity and fluidize the whole bed, which enables homogenous rinsing of the bed. The opening of the distributor is larger than the mean grain size of the filter bed material and allows fiber, pieces of plastic and similar impurities to pass through the distributor and be removed from the filter.