Abstract: An apparatus of an elongated polygon-shaped vessel having a longitudinal axis, and an internal volume, wherein the elongated vessel is rotatably mounted about its longitudinal axis, and wherein optionally, the internal volume is divided into a plurality of transverse chambers having a polygonal cross-section shape, and can optionally be further divided into a plurality of longitudinal sections, an inlet for receiving material, and an outlet for removing material, is useful, for example, as a composter for municipal solid waste (MSW), source separated organic waste, yard waste, sewage sludge, and of organic hazardous waste, as a wet mill to reduce the sizes, mix, and screen materials, such as MSW, source separated organic waste, yard waste, sewage sludge, and organic hazardous waste, and as a rotating vessel, such as a cement kiln or ball mill.