The filter apparatus for an incoming liquid which includes a retentate and a permeate includes a housing with a frame and a hollow drum assembly mounted for rotation within the housing about a fixed central cylinder. The drum assembly has openings in the drum wall. An inlet assembly delivers the incoming liquid under pressure to the drum assembly. A filter assembly is mounted to the inside of the drum. A trough assembly is mounted so as to be in communication with the central cylinder and is in a fluid-tight relationship to the interior surface of the filter assembly as the drum rotates past the trough assembly. A manifold is fixedly mounted but has a substantially fluid-tight relationship with the exterior of the drum, and is configured to cover successive columns of drum openings as the drum rotates. Pressurized gas is directed to the manifold at selected times, such that as the drum turns, and retentate is collected on the interior surface of the filter as the incoming liquid is forced through the filter assembly, pressurized fluid from the manifold dislodges the retentate off into the trough and out the outlet assembly.