NOVELTY - Composting device comprises a composting tank (2, 7) rotatable about a fictitious axis of rotation. An air duct (12, 22) is provided for air exchange between the interior and the exterior of the composting tank. It extends through a wall part (11, 21) of the composting tank into the interior of the composting tank, which wall part is on a side (10) of the composting tank, intersecting the axis of rotation.    USE - The device is used for composting material containing organic matter.    ADVANTAGE - The device results in a more effective aeration with the rotatable composting tank. The air duct aerating or deaerating the composting tank. Aeration and/or deaeration can take place in a natural manner, or by fans and/or compressors. It extends into the interior of the composting tank, and services the material situated further down the tank. During aeration, introduced air is prevented from leaking away prematurely and, in case of deaeration, ambient air is prevented from being drawn in at the deaeration side. As the first wall part is at first side of the composting tank, intersecting the axis of rotation, the location where the first air duct extends through the first wall part of the composting tank can be in the direct proximity of the axis of rotation. The air duct is held effective position for aeration when the composting tank is rotated.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for composting material containing organic matter. A conveyor screw (16, 26) is located in the interior of the air duct. The axial direction of the conveyor screw is parallel to the longitudinal direction of the air duct. The conveyor screw operatively returns into the composting tank material from the composting tank having ended up in the air duct. The wall part and/or the air duct are bearing-mounted in a wall part of the composting tank which, during rotation of the composting tank, rotates along with the composting tank. The air duct aerates the composting tank. The walls of the air duct located in the interior of the composting tank are perforated for air passage from the interior of the air duct to the interior of the composting tank. The air duct terminates in the interior of the composting tank above the level to which the composting tank is filled with the material.    DESCRIPTION OF DRAWING(S) - The figure shows, in side view, a longitudinal cross section of a composting device.    Composting tank (2, 7)    Side (10)    Wall part (11, 21)    Air duct (12, 22)    Conveyor screw (16, 26)