Abstract: A filter apparatus having a backwash head arranged to up-flow backwash one filter cell at a time, and a scavenging means having a fluid intake head arranged to communicate with at least two cell ports at the same time to downflow scavenge each filter cell the first time when the backwash head is in a position to backwash one filter cell and a second time when the backwash head is in a position to backwash a succeeding filter cell. Turbidity monitoring means having a monitor inlet conduit mounted on the fluid intake head, is arranged for communication with the cell port adjacent the end of the fluid intake head that trails during the backwash run, to monitor turbidity of fluid from each cell port only after the associated filter cell has scavenged at least once.

Abstract: A method and apparatus for cleaning a filter apparatus in which liquid influent is passed through web filter material on a rotatable filter frame into a filter effluent compartment and wherein the filter material is intermittently backwashed during a filter time by a suction device at an outer side of the filter material which draws filtered liquid from filtered effluent compartment in a backwash direction through the filter material, and wherein the filter material on the filter frame is subjected to a wash operation during a wash time by directing a high pressure liquid spray at one side of the filter material. The pressure in the suction device during backwashing is monitored, and the wash operation is initiated after the pressure in the suction device reaches a preselected sub-atmospheric pressure.