PURPOSE: To wash scum of sewage, sludge, etc. surely in a short time with a small amt. of water by partitioning the inside of a water tank to a washing tank and a dust removing tank, producing swirling flow and reverse swirling flow in the washing tank to wash the scum then passing the water into the dust removing tank.

CONSTITUTION: The inside of a water tank 10 is partitioned to a washing tank 14 and a dust removing tank 16 by means of a movable partition plate 12. Scum is charged into the washing tank 14 and air diffusion nozzles 18, 20 are opened alternately to generate swirling flow and reverse swirling flow alternately in the tank 14, whereby the malodorous components in the scum are eluted. After the washing, swirling flow is generated by the nozzle 18 and at the same time, the plate 12 is slightly moved upward to form a water passing clearance. Further, transfer flow is injected toward the water passing clearance through a transfer nozzle 28 to feed the scum in the tank 14 into the tank 16. Thereafter a dust removing device 34 is driven to carry out the stuck and recovered scum by means of a carrying out device 40. The scum is recovered easily by such mechanism without requiring fresh water.