PURPOSE: For efficient sludge treatment with reduced period for filtering, dehydration, and evaporation, high pressure gas is introduced into sludge which is then dried in a sun drying bed.

CONSTITUTION: Various treatment processes of sewage, industrial waste, etc. produce sludge. Such sludge is introduced into a closed agiter where it is mixed with high pressure air or other gases, alternatively with compressed water containing dissolved high pressure air. This causes solid material in the sludge to combine with bubbles, reducing its apparent density and flow up as porous solid material, leaving clear water at lower section. Further treatment in a sun drying bed facilitates filtering the separated water and evaporating water from the porous solid material. The process, thus, effectuates reduced period for filtering, dehydration, and evaporation as well as saving for processing area.