PURPOSE: To reduce easily and efficiently the generation of malodors and perform above mentioned dehydration and removal of settled sludge, by adsorbing settled sludge on the surfaces of moving bodies, and dehydrating the same then moving the sludge to a prescribed position to cut off the exertion of a negative pressure and exerting the own weight or a positive pressure thereon.

CONSTITUTION: Sewage is supplied through an inflow port 3 into a settling tank 1, and the greater part of water is removed through an overflow port 4 and the settled sludge through an opening 5. Roll assemblies 6, 6' for adsorption provided in the opening 5 consist of hollow stationary shafts 7 and clad cylindrical shafts 8, and are rotated while the shafts 8 are brought into tight contact with each other. The sludge is thus adsorbed onto the adsorption surfaces 13 consisting of screen nets 14 on the surfaces of the assemblies 6, 6' by the effect of the negative pressure generated by a vacuum generator 16 consisting of a vacuum tank and a jet pump, whereby the sludge is dehydrated. The dehydrated water is contained in a vacuum tank. The adsorbed sludge is rotated and moved to the position of the injection port 12 of the shafts 7 and is removed continuously by the positive pressure of a compressor 17 from the port 12 so as to be dropped onto a transfer belt 19.