The separation efficiency of Total Suspended Solids in a DAF cell depends substantially on the generation of uniformly sized microscopic air bubbles.
A part of the clarified water, generally 25 to 30% of the feed rate, is pressurized through a centrifugal pump to about 65 meter head and let into a cylindrical Air Mixing Tube through a nozzle at one end. The nozzle is so oriented inside the tank that the jet of water churns spirally along the inside wall of the tube forming a vortex along the central axis of the tube.
Into this tube is brought compressed air which passes through a microscopically porous medium placed adjacent to the inside wall of the tube.
The tube produces a saturated air-water mixture because the rate of absorption of any gas in a liquid is directly proportional to the pressure in which the dissolution takes place.
The air-water mixture that comes out of the other end of the tube passes through a pressure release valve where the pressure is reduced to the level of the incoming wastewater feed. At this stage, air bubbles of 30 - 50 microns are produced profusely which get released into the wastewater thereby giving the necessary buoyancy
to the suspended solids to rise to the surface of the water in the flotation tank.