Flotation unit

As opposed to settling, flotation is a solid-liquid or liquid-liquid separation process which is applied to particles whose density is lower than that of the liquid they are in. In water treatment flotation units are mainly used for oil separation and for sludge separation.

Flotation units can be:
1.Dissolved Air Flotation (DAF), Dissolved Gas Flotation (DGF), Induced Air Flotation (IAF), Induced Gas Flotation (IGF).
2.Compact Flotation units.

Dissolved-air flotation is a very effective solid-liquid separation process used in water treatment, as an alternative to sedimentation, to lower the solids concentrations before granular filtration. Compared to sedimentation, the advantages are:
smaller surface and volume;
better treated water quality;
higher concentration of thickened sludge.

The removal is achieved by dissolving pressurized air in the water. The dissolved air releases thousands of tiny bubbles which are able to carry to the surface the flocs. This system is used where the suspended solids are in low concentration and their specific gravity approaches the one of the water. The system is interesting in case of low temperature or for sedimentation of water containing light suspended solids as algae, organics, colours, fuel, BOD, COD, lube oils, etc.

Similar applications are:
dissolved Gas Flotation (DGF): in some application DGF units do not use air as the flotation medium due to the
  explosion risk, but Nitrogen gas is used instead to create the bubbles;
induced Gas Flotation (IGF): treatment process that clarifies wastewaters (or other waters) by the
  removal of suspended oil;
induced Air Floatation (IAF): a variant of the DAF unit that is commonly used in oil fields and for ballast water treatment.

Increasingly stringent environmental discharge requirements plus the constant pressure to reduce equipment footprint have led to the development of the Compact Flotation Unit. These systems are ideally suited for offshore applications and for oil separation from water.
The Compact Flotation Unit is based upon a complex combination of multiple separation techniques. It operates by combining the well-established principles of gas flotation, oil droplet coalescence and centrifugal separation into a single process unit.
The system can operate in single step unit or in series units.