In a composter having a horizontally elongated rotating drum, material is fed into the drum through an opening in a stationary end plate having an annular marginal area which overlaps, in sealing relationship, an annular intake end wall of the drum. Material passes through a central opening in an annular exit end wall of the drum, and falls by gravity onto a cylindrical screen which is fixed to, and rotates with, the exit end wall. The annular end walls are in axial register with, and surrounded by, external trunnions on the drum which ride on pairs of supporting rollers. Frusto-conical rings are welded to the end walls, and to the inside of the drum at locations opposite the edges of the trunnion rings to reduce metal fatigue. The exit end rollers allow for axial expansion of the drum. The interior wall the drum is lined with a rubber.