To attain a dried product with a value less than a specified moisture rate by a method wherein a liquid material having a specified moisture rate not less than a specified percentage is changed by a flask type vacuum drying machine into a cake and further fed into a cylindrical aeration agitating drying machine.

A material such as a syotyu distillation waste liquid or surplus sludge discharged from a sewage processing plant or raw sewage having a high moisture rate of more than 90% is rapidly condensed down to a moisture rate of about 50 to 60% under an operation of a flask type vacuum driving machine 1 capable of evaporating and dehydrating into surrounding gaseous phase from its surface. The condensate is one taken out after about 2 hours and fed into the cylindrical aeration agitating and drying machine 18 through a shooter 37. Material condensed by the flask type vacuum drying machine 1 and formed into a cake- shape like sake-kasu or the like mat receive hot air from below while it is being agitated on a porous bottom plate 22 of the cylindrical aeration agitating and drying machine 18. With such an arrangement as above, moisture content in the material can be efficiently evaporated and such material as the one having a moisture rate of 10% or less is dried at a fast evaporating speed without damaging an agitating vane 2. The dried product is utilized as a rough feed having high quality and also the dried may become an organic fertilizer of high quality.