Dissolved Air Flotation

Dissolved Air Flotation, referred to by its acronym of DAF, is a method of removing contaminants from wastewater that have a tendency to float, such as fine solids. Pressurized air is injected into a water stream which is commonly sourced from post-treatment clarified water. That water is mixed with the incoming untreated water where the dissolved air is no longer pressurized and comes out of the solution in tiny bubble form. These bubbles attach to the contaminants and together they rise to the surface. The contaminants can then be skimmed off and disposed. Clarified water exits through the bottom of the tank to ensure the floating contaminants do not continue past the unit.

Figure 1: Diagram of a DAF unit (Komline-Sanderson, 2015)

The solids to be removed may be too fine to be caught by the rising bubbles. In these cases, coagulants and/or flocculants are used to aggregate them into larger clusters. The coagulants and flocculants are added either in a preceding tank or piping system.
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DAF systems will have a smaller footprint than a settling system as there is more active movement in a DAF system. It is an indoor system as it should not freeze. The timing of any chemical additions for aggregation of soils must be carefully considered as it will take time to properly bind the solids. If they are added too close to the DAF, full flocculation will not occur and that chemical will be wasted.

​References

• Mundi, G. S. (2013). Assessment of Effective Solids Removal Technologies to Determine Potential for Vegetable Washwater Reuse (Master's thesis). NovemberRetrieved from https://atrium.lib.uoguelph.ca/xmlui/bitstream/handle/10214/7737/Mundi_Gurvinder_201312_Msc.pdf?sequence=3
• Komline-Sanderson. (2015). Applications. In Dissolved air flotation. Retrieved December 14, 2015, from http://www.komline.com/images/tab_DAF_app.png