Principles of Dissolved Air Flotation
Dissolved Air Flotation (DAF) is used as a method to separate contaminants from various wastestreams.
When a gas is mixed with a liquid under pressure, the gas dissolves into that solution. When the pressure is
released, the gas escapes and forms tiny air bubbles in the liquid. These tiny bubbles attach themselves to
any solids and coagulated material and carry it to the surface.
The patented Redux™ Clarifier accumulates the floating mass at the top of the cone. This floating
mass of contaminants is held there by the constant stream of bubbles rising in the Clarifier [see below].
| Phase 1 |
Phase 2 |
Phase 3 |
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| figure 2. Flow Chart of a patented Redux™ Clarifier DAF |
In Phase 1, clean water from the bottom of the Clarifier flows back to the process or to discharge. As
the mass in the top of the Clarifier grows, the discharge of clean water is interrupted by closing the discharge
valve, causing the level in the Clarifier to rise. The contaminants are forced out the top of the Clarifier and
collected for further dewatering in Phase 2. When the discharge valve opens in Phase 3, clean water
again flows to the process.
DAF Theory
Henry's Law
The amount of air that can be absorbed by a liquid is directly proportional to the pressure of the gas.
Simply stated, at a constant temperature, the greater the pressure the more air can be absorbed into water.
Nucleus Theory
Tiny bubbles coming out of solution will attach to any small particle
(the contaminants in the waste water), forming life jackets of the contaminants and carrying them to the surface.
Stokes Law
The combining of a sufficient number of air molecules with the contaminants results in the combined air/solids
mass having a specific gravity which is less than the liquid. Therefore, the solids that would eventually settle
or remain in suspension float to the surface where they can be removed from the top of the cell.
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