Abstract: Disclosed is a bioreactor apparatus having a bed of buoyant media pellets floating within a filtrate to be processed. The apparatus includes a tank having a peripheral wall for containing filtrate and a bed of media pellets. A central manifold is rotatably supported within the tank the central manifold being mounted for rotation about a vertical axis and having a plurality of longitudinally spaced openings intermediate its ends, the openings adapted to eject filtrate in a generally horizontal direction and along a substantially vertical plane toward the wall of the tank. A thrust manifold, generally parallel to the axis of the central manifold has a plurality of longitudinally spaced openings intermediate its ends directed horizontally and generally perpendicularly to the plane. The thrust manifold is supported in association with the central manifold inwardly adjacent the tank wall and offset rearwardly of the plane to rotate with the central manifold.