Abstract: An apparatus for drying moist solid or semi-solid materials, such as sewerage sludge, municipal waste, industrial waste, agricultural waste, and the like, includes a dryer unit having a plurality of stacked heating chambers, each of the heating chambers above the lowest heating chamber having a conveyor belt for transporting the material through the associated heating chamber and depositing it on a lower heating chamber, the lowest of the stacked heating chambers including a conveyor belt for transporting the material therethrough and discharging the material from the dryer unit. The apparatus utilizes a combination of convective heat transfer, in the form of a heated gas which rises upwardly through the dryer unit through successive heating chambers, and radiative heat transfer, provided by radiative heating units disposed above the conveyor belt in each heating chamber.