Abstract: Each face of the disc for sewage aeration includes a multiplicity of recesses. The recesses of one face have no communication with those of the other face and are precisely dimensioned so that the sewage, which is essentially water, flows into and out of each recess without leaving an accumulation of deposits in the recess. This is accomplished with no reduction of and possibly an increase in the aeration efficiency of the disc.

Abstract: The specification discloses an improvement in rotary drum screens for the filtration of liquids which comprise (a) a drum having a central horizontal axis and a radially outer surface, (b) a plurality of microscreen grids mounted on the radially outer surface of the drum, each of the microscreen grids comprising a screen which is divided into a large number of small cells by walls which extend radially with respect to the drum, (c) means for introducing the liquid to be filtered into the interior of the drum, (d) means for rotating the drum about its central axis, (e) a backwash header mounted outside the radially outer surface of the drum, and (f) a backwash receiving trough mounted within the drum for collecting filtrate accumulated on the screen. The liquid to be filtered is introduced into the drum at one end thereof, and the drum is supported so that it is partially submerged in the filtered liquid.