DAF is a gravity seperation process whereby the separation of two phases is achieved by increasing the specific gravity difference of the two phases. This is achieved by attaching micro air bubbles, brought about by saturating water with air under pressure, and then expanding the wa terstream through valves to atmospheric pressure. These micro bubbles nucleate onto the solid particles to be separated, thus lowering the specific gravity and allowing contaminants to rise to the surface.
Suspended solids, grease and oil are very efficiently removed by DAF, and a combination of screening and DAF results in BOD/COD removals upto 60% depending on the application.However, a combination of flocculation and floatation can result in BOD removals of around 80-90%.