Modern high rate DAF clarifiers have advanced to such an extent that they could overshadow conventional settling clarifiers in wastewater treatment. 

DAF hydraulic loading has increased from 1 L/m2.s to 2.5 L/m2.s and for a triple stacked unit to 7.5 L/m2.s. The detention time has decreased from 30 minutes to 3 minutes. Air dissolving is improved and now requires only 10 seconds retention time in the air mixing tube instead of the previous 60 seconds. The smaller size and weight of a modern DAF unit allow for inexpensive construction and flexibility of erection using prefabricated units. The availability of excellent flocculating chemicals gives a high stability of operation and high clarification degree.

DAF ADVANTAGES

Low capital and operational costs
Continuously self-cleaning
Totally integrated
Minimal maintenance
Space saving and low foundation costs
High quality clarified water

high chemical efficiency

Easily relocatable 

Wock-Oliver's DAF , Dissolved air floatation clarifier has been widely used for industrial wastewater treatment. The typical industrial wastes treated by flotation are paper mill backwater, oily wastewater as well effluents from sugar, dairy, textile industries and tanneries.

Process description[edit]

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 coagulate the colloidal particles and/or a flocculant to conglomerate the particles into bigger clusters.

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. Bubbles form at nucleationsites[4] on the surface of the suspended particles, adhering to the particles. As more bubbles form, the lift from the bubbles eventually overcomes the force of gravity. This causes the suspended matter to float to the surface where it forms 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.[1]

Some DAF unit designs utilize parallel plate packing material (e.g. 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.