Process Description
The feed water to the DAF float tank is often (but not always) dosed with a coagulant (such as ferric chloride or aluminum sulfate) to flocculate the suspended matter.
A portion of the clarified effluent water leaving the DAF tank is pumped into a small pressure vessel (called the air drum) into which compressed air is also introduced. This results in saturating the pressurized effluent water with air. The air-saturated water stream is recycled to the front of the float tank and flows through a pressure reduction valve just as it enters the front of the float tank, which results in the air being released in the form of tiny bubbles. The bubbles adhere to the suspended matter, causing the suspended matter to float to the surface and form a froth layer which is then removed by a skimmer. The froth-free water exits the float tank as the clarified effluent from the DAF unit.
Some DAF unit designs utilize parallel plate packing material, lamellas, to provide more separation surface and therefore to enhance the separation efficiency of the unit.
DAF systems can be categorized as circular (more efficient) and rectangular (more residence time). The former type requires just 3 minutes; an example is a Wockoliver DAF system. The rectangular type requires 20 to 30 minutes; a typical example is a Syskill DAF system. One of the bigger advantages of the circular type is its spiral scoop.
Read more about this topic: Dissolved Air Flotation
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