A rotary disk filter and a module for building a filter support for a rotary disk filter are disclosed. The rotary disk filter may comprise a drum, which is rotatable about its central longitudinal axis. The rotary disk filter may be adapted to receive a liquid which is to be filtered. In one implementation, the rotary disk filter may comprise at least one disk-shaped filter member which on the outside of the drum extends outwards in the transverse direction of the drum, and which has a filter support and at least one filter portion supported thereby. A first liquid duct may extend from the drum through the filter member and out through the filter portion. The filter portion may be made of filter segments, which are detachably secured to the filter support. At least one second liquid duct may extend between adjoining filter segments to provide liquid communication between the filter segments. The module may comprise two inner support portions and two outer support portions for at least partial enclosure of two adjoining filter segments, and an intermediate support portion adapted to be arranged between the two adjoining filter segments.