PURPOSE: To make it possible to dry a dehydrated sludge cake without requiring fuel cost and to attain effective utilization of sludge, by using the dry excretion residue obtained by drying a dehydrated excretion residue without requiring fuel cost as fuel.

CONSTITUTION: The excretion residue 3 removed from excretion 1 is dehydrated by a dehydrator 8 such as a screw press dehydrator to obtain a dehydrated excretion residue 9 with water content of about 60%. This dehydrated excretion residue 9 is supplied to a hermetically closed aerating dryer 10 to form a packed bed. Air 12 emitted from an aeration blower 11 for supplying oxygen necessary for the respiration of microbes is introduced into the aeration tank of a biological treatment process 5 from the lower part of the aerating dryer 10 to perform the aeration drying of the dehydrated excretion residue. By passing the emitted air of the aeration blower 11 through the dehydrated excretion residue in the aerating dryer 10, the dehydrated excretion residue 9 can be effectively dried without requiring cost to obtain a dry excretion residue 13. This excretion residue 13 is incinerated in an incinerator 20 as solid fuel and utilized as a heat source.