Fixed-disk filter units for dewatering industrial sludges, including paper sludges, municipal sewage, tertiary filtration, water reuse, process streams, and surface water treatment that reduces overall horsepower and permits removal of each individual disk while the filter remains in operation, the filter consisting essentially of a plurality of fixed filter disks which remain fixed while a rotating center shaft supports respective backwash arms for backwashing each filter disk, the rotating center shaft serving as a header for removal of solids from the filter, a timer for timing a backwash cycle, which is initiated by headloss across the filter, electrically actuated valves for segregating the backwash header and clean the filter disks on that portion of the header, insuring complete cleaning of the filter cloth while minimizing the rate at which backwash water is returned to a treatment facility