PURPOSE: To obtain a dried fuel containing a large amount of organic components, being readily burnt, moldable into any shape, by immersing sewerage sludge, etc., in a hot oil in a closed container and dehydrating the sludge by heating under a specific condition under reduced pressure.

CONSTITUTION: Sludge produced by treatment process or final process for BOD, COD, etc., of dehydrated and evaporated water, washed water, steamed water or steaming for animal containing gelatin, protein, etc., chicken, fine bone, internal organ, skin, feather, etc., or sludge of precipitated coagulated component in sewerage is immersed in an oil preheated at about 60W90°C in a closed container. Then the sludge is heat-treated in a heated animal oil, fish oil or a vegetable oil as a heating medium while controlling the oil temperature in the container by stirring under low reduced pressure at 10W20mmHg initially and then under high reduced pressure at 740W750mmHg, the sludge is dehydrated and taken out from the closed container to give the aimed fuel.