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. 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 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 and configured to cover successive columns of openings of the drum wall as the drum rotates. Pressurized gas is directed to the manifold, so that as the drum turns, and retentate is collected on the interior surface of the filter, pressurized fluid from the manifold dislodges the retentate into the trough and out an outlet assembly.