The effluent enters the feed compartment and flows into the space between the filter discs. It flows through the mesh, passing to the discharge compartment, while the solids are retained on the filter disc surface. As the amount of retained solids increases, they tend to agglomerate and, due to the rotation of the discs, to crawl over the filter surface, exerting a cleaning effect. Once the retained solids exceed a certain volume, the machine starts to discharge them automatically. The filter screens are periodically cleaned by a system of backwashing nozzles.