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What is dissolved Dissolved Air Flotation (DAF)

Dissolved air flotation (DAF) techniques are generally used to remove insoluble impurities, fats and oils from a liquid. Flotation is also often used to remove the (light) flocks formed during coagulation from the effluent stream.

Dissolved air flotation

The air is dissolved in the water under pressure (higher saturation concentration) in a pressure vessel. By subsequently reducing the pressure again, relaxation, small gas bubbles are created in the order of magnitude of 20-60 µm. These micro air bubbles are introduced into a flotation unit to remove substances from the water by means of flotation. The removal takes place by attaching small air bubbles to the contamination, after which it floats to the surface. The contamination floating on top of the liquid is then removed with a scraper. The formation and distribution of water and air plays an important role in this.

Applications of dissolved air flotation

Dissolved Air Flotation techniques are generally used to remove insoluble impurities, fats and oils, heavy metals, suspended matter, sludge and other impurities from a liquid. Often used to treat waste water to lower the COD values prior to discharge into a sewer or biological treatment in a WWTP.

Type and implementation of flotation

The choice of which flotation unit is most suitable for the water to be treated depends on the substances present (sludge content), the possible pre-dosing of chemical aids in a coil pipe flocculator and of course the desired capacity. Some embodiments of the flotation unit also have a lamella package (internal) or a sand trap. The Flotation units from Logisticon Water Treatment can be supplied in stainless steel, plastic (glass fiber reinforced) or steel coated.

Difference between DAF and IAF

Air bubbles can be introduced into the fluid stream in various ways. When this happens by dissolving the air in a pressurized liquid stream and releasing it into the installation, we speak of "dissolved air flotation" also called DAF. The micro gas or air bubbles are created in the order of magnitude of 20-60 µm. Air or gas can also be introduced into the water mechanically, with the help of porous elements and / or rotating elements, air/gas is introduced at the bottom of the tank. This results in air bubbles with a size of 1-3 mm. We then speak of "induced air flotation" or IAF. Logisticon applies DAF flotation in most cases. They can be rented or bought. If a DAF flotation is combined with a filtration, this is called DAFF: Dissolved Air Flotation Filtration.

Alternative to air one can also use nitrogen. This is often used in a dangerous environment, such as volatile substances that which can burn or explode in combination with oxygen.

What does flotation look like?

The effect of flotation is shown in the picture. The relaxation of the air introduced into a holding tank at the right place in the flotation installation causes the formation of tiny air bubbles, which carry the suspended contaminants to the surface. The effectiveness of the technique can be controlled, amongst other measures quite well by varying the air dosage. With DAF flotation it is possible to separate emulsions from organic liquids (oil or fat in water) in addition to floating flocks and solids in some cases. The flotation installations can also be equipped with a lamella package for those contaminants that are too heavy to float. There is then a separate sludge drain for this.