It is the separation of the pollutants in the wastewater, especially oil, from the wastewater by floating with microbubbles. The microbubbles are formed by dissolving the air in water under pressure to remove a portion of the treated water. Dissolved air is recirculated back into the DAF system and the flocks are deposited on the surface as a result of contact with the flock particles. Heavy particles precipitate to the bottom. Foam and bottom sludge deposited on the surface are taken to sludge dewatering units. Treated water is discharged from the outlet sluice with its charm.