Dissolved air flotation is a wastewater treatment machine that clarifies wastewaters (or other waters) by the removal of suspended matter such as oil or solids. The removal is achieved by dissolving air in the wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank.

The released air forms tiny bubbles which adhere to the suspended matter causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device. Generally standard DAF dissolved air flotation machine is enough for most of the wastewater treatment applications, you don't need a sludge hopper at tank bottom, unless the wastewater contains a little more heavy solids.

The feed water to DAF dissolved air flotation machine is often (but not always) dosed with a coagulant (such as ferric chloride or aluminum sulfate) to coagulate the colloidal particles and/or flocculants to conglomerate the particles into bigger clusters.

A portion of clarified effluent water leaving the DAF tank is pumped into a small pressure vessel (called air drum or saturator) into which compressed air is also introduced. This process saturates pressurized effluent water with air under pressure(2.5-4kg/cm²).

The air-saturated effluent water 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. This immediately results in the recycled effluent water becoming supersaturated with air as millions of tiny bubbles form(Φ5-20μm).

These bubbles attach to, and form within, the solids or chemical flocculants entering the vessel, causing them to float to the surface where they are retained and subsequently removed by a skimmer.