• Dissolved air flotation (DAF) is a widely used clarification process. DAF removes particles from water using air bubbles that collide and attach to particles. The particle bubble aggregates are then separated once they rise to the surface of the tank.
  • It has applications in several fields which include drinking water, municipal and industrial wastewater, in situ treatment of lakes for algae and seawaters for algae and oil spills.
  • The most common method of producing air bubbles is the pressurized recycle flow method. In this method, a recycle flow of treated water is pumped to a saturator vessel where air is added under pressure and dissolved.
  • The pressurized-recycle flow from the saturator is then introduced into the contact zone of the DAF tank. The pressure change across nozzles causes the dissolved air to come out of the solution in the form of small air bubbles.
  • Influent from equalization tank is pumped to the DAF unit before flocculation. After DAF unit, the wastewater goes to flocculator for further removal of TSS and then it moves to the aeration tank for proper aeration

Advantages of using DAF over other clarification processes

  • DAF is more efficient in removing low-density floc then sedimentation processes.
  • The problem of algae clogging filters and reducing filter run times usually occurs in the plants. But DAF is effective in removing algae from water supplies. In fact air bubbles formed in DAF can also remove some taste and odour compounds from the water which can be consider as a secondary benefit.
  • DAF is more effective than sedimentation in removing pathogens such as Giardia cysts and Cryptosporidium oocysts.
  • DAF plants have a lesser footprint compared to sedimentation plants on account of smaller tanks. In some cases DAF is placed over filtration reducing the plant footprint further.
  • DAF produces floating sludge with higher percent of solids which possibly reduces sludge treatment and disposal.
  • Energy savings is higher in DAF compared to sedimentation plants as smaller motors are used to run the flocculator, longer filter runs, and less filter backwashing of filters.