Dissolved air flotation (DAF) is one of the most versatile and effective processes in water, wastewater and desalination treatment.

Dissolved air flotation (DAF) is one of the most important and effective processes in the treatment of all types of water, both in industrial and urban wastewater treatment, water processing, water reuse and desalination processes. It can be installed at different points of the water treatment line due to the multiple design possibilities of the dissolved air flotation units.

On several occasions, the dissolved air flotation system is installed at the beginning of the water treatment process, immediately after pretreatment to remove grease and oil. It can also be installed at the biological treatment inlet to reduce the pollutant load. On many other occasions, it is placed at the end of the water treatment line to clarify the water before it is discharged. In desalination, where the development of fiberglass is beginning to establish itself as a construction material, it also works to protect membranes from the presence of algae in the water. In addition, it can be installed at the top of the sludge treatment line as a sludge thickener to reduce the volume. Dissolved air flotation is based on a physicochemical process that separates solid and liquid particles by the addition of very small air bubbles. . These bubbles adhere to the solid particles and give them a high upward velocity. Once on the surface, the solids, the sludge, are mechanically extracted into the hopper. Dissolved air flotation provides a rise rate 5 times higher than the settling rate in a conventional settling tank, which saves time and space.

Flocculation and coagulation

The wastewater is constantly pumped into the flocculation tube, a zigzag-shaped tube that facilitates the mixing of the water with the chemical reagents. The coagulant is added there. This chemical can destabilize suspended particles or colloids to facilitate subsequent solid-liquid separation. Some of the most commonly used coagulants in water treatment are aluminum sulfate, ferrous sulfate, ferric chloride or aluminum polychloride.

Then, in the same tube, the flocculant is added. This is an oppositely charged polymer to attract smaller flocs or colloids to form larger flocs. In this way, micro air bubbles adhere to the larger flocs to create particles with less density than water and make flotation possible.

Sludge on one side, water on the other side

After solid-liquid separation, a portion of the treated water, approximately 30%, is recirculated to be mixed with wastewater. A developed injection system distributes the saturated water pressure in the flotation unit. In this way, the bubbles generated can reach the ideal size to favor floc flotation.

Finally, on the surface of the flotation unit, a scraper system carries the sludge generated towards the hopper to collect it, while the clarified water is discharged into a drainage channel on the opposite side. Meanwhile, the heavier particles that could not reach a density lower than that of the water are kept in the sedimentation chamber to be recirculated to the beginning of the water treatment line and receive the appropriate treatment.