To dry sludge to be treated at one time in a shorter period than the conventional method.

In a sludge drying method, a primary sludge drying vessel 1 where water contained in sludge M fed onto filter sand 4 passes through the filter sand 4 and sand pipes 5 to be discharged from a drain hole 3 in the bottom 2a of a drying vessel body 2, and a secondary sludge drying bed 8 connected to the side of the primary sludge drying vessel 1 are used. About 2/3 of the upper layer of the sludge M in the primary sludge drying vessel 1 is transferred to the secondary sludge drying bed 8 to be extended therein when the water content of the sludge M in the primary sludge drying vessel 1 becomes equal to or less than about 75%, and the sludge M in the secondary sludge drying bed 8 is discharged from it when the water content of the sludge M in the secondary sludge drying bed 8 becomes equal to or less than about 40%. Subsequently the sludge remaining in the primary sludge drying vessel 1 is transferred to the secondary sludge drying bed 8, and then new sludge to be treated is fed into the primary sludge drying vessel 1.

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