What is flotation?

Flotation is similar to sedimentation in that suspended particles are separated from the water by their dissimilar densities. The difference is that in flotation the particles rise to the surface because they are lighter than water. They may be naturally lighter than water, such as oil (natural flotation), or be made lighter than water by the use of air bubbles which attach themselves to the particles (air flotation).


A much-used flotation installation is the Dissolved Air Flotation (DAF) unit. In this unit, air is dissolved in water under high pressure. The air-water mixture is subsequently fed into a flow-through tank that is subject to a partial vacuum. Because pressure in the tank is lower, small bubbles will form in the water. These air bubbles attach themselves to the suspended particles present and carry them upwards. A scraper continually scrapes the surface sludge out of the tank.