NOVELTY - Organic material is dried by bringing the total solids content to 30% to permit composting, then processing by batches. Each batch is divided into phases, the first by breaking the cell structure of the organic material by composting and reducing the moisture content to 65-55%; the second by thermal drying using energy external to the batch, preferably produced from composting other batches.    USE - For drying organic material e.g. sludges and other possible support substances for the manufacture of fuel.    ADVANTAGE - The process is simple, manageable and environmentally friendly. It can be used to manufacture fuel efficiently and economically from odorous sludges and other organic materials because the free energy of the process itself is used for drying and the end product can replace conventional fuels for existing boilers without any special arrangements.    DETAILED DESCRIPTION - The organic material from sludges and possible support substances for the manufacture of fuel is dried utilizing mechanical composting by bringing the total solids content of the organic material to 30% to permit composting, and the mixed and pre-dried materials are divided into batches where each batch is processed in two principal phases. In the first phase, the cell structure of the organic material is broken by composting to permit thermal drying and the moisture content is reduced to 68-50, preferably 65-55%, and in the second phase, the materials of the batch are dried using thermal energy external to the batch, preferably produced by composting other batches.    An INDEPENDENT CLAIM is included for a tunnel composting plant for manufacturing fuel from organic materials and possible support substances using mechanical composting comprising several composting tunnels (13) with an air treatment system that includes duct damper devices (11) that can be independently operated on the feed side so that fresh air and circulation air in an optional ratio can be connected to the air feed of each composting tunnel, a fresh air feed system with heating devices (17), an exhaust air system with gas scrubbing devices (15), and a circulation air system (14,18,19) to lead the exhaust air back to the composting tunnels.    DESCRIPTION OF DRAWING(S) - The figure shows a composting plant especially for drying.    Duct damper devices (11)    Composting tunnels (13)    Duct dampers (14)    Gas scrubber (15)    Heating devices (17)    Main auxiliary exhaust duct (18)    Auxiliary exhaust duct (18')    Circulation air duct (19)