Industrial wastewater often contains suspended solids, oil, grease, and other contaminants that must be removed before biological treatment or discharge. One of the most effective technologies for removing these pollutants is the Dissolved Air Flotation system, commonly known as DAF.
In this article, we explain how DAF works, its key components, and why it is widely used in industrial wastewater pretreatment.
What Is Dissolved Air Flotation (DAF)?
Dissolved Air Flotation (DAF) is a physical-chemical wastewater treatment process that removes suspended solids (SS), oil, grease, and other floating materials.
The process works by dissolving air in water under pressure and then releasing it at atmospheric pressure in a flotation tank. This creates very fine microbubbles, which attach to contaminants and float them to the surface for removal.
DAF systems are widely used in industries where wastewater contains high levels of solids or fats that are difficult to settle.
Working Principle of a DAF System
A typical DAF system works through several key steps:
Chemical Conditioning
Before entering the DAF unit, wastewater is usually treated with chemicals such as:
Coagulants (e.g., PAC or alum)
Flocculants (polymer)
These chemicals cause small particles to combine into larger flocs, making them easier to float.
Air Dissolution
A portion of treated water is recycled and saturated with air in a pressure tank.
Under high pressure, air dissolves into the water.
Microbubble Formation
When the pressurized water is released into the flotation tank:
Pressure drops suddenly
Dissolved air forms microbubbles (20–50 μm)
These bubbles attach to suspended particles.
Flotation Process
The bubbles lift the contaminants to the surface of the tank, forming a floating sludge layer.
A mechanical scraper then removes the sludge.
Meanwhile, the clarified water flows out from the bottom or side of the tank.
Main Components of a DAF System
A typical DAF unit includes the following components:
Flotation Tank
The main separation zone where bubble-particle flotation occurs.
Air Dissolving System
Includes:
Air compressor
Pressure tank
Recycle pump
This system generates the microbubbles.
Chemical Dosing System
Used to add coagulants and polymers for better separation.
Sludge Scraper
A chain or rotating skimmer that removes the floating sludge layer.
Effluent Collection System
Ensures clarified water exits the unit efficiently.
Advantages of DAF Systems
Compared with traditional sedimentation tanks, DAF systems offer several advantages.
High Removal Efficiency
DAF is particularly effective for removing:
Suspended solids
Oil and grease
Algae
Fine particles
DAF vs Traditional Sedimentation
Although sedimentation tanks are widely used, they are not always effective for wastewater containing:
Low-density solids
Oil and grease
Very fine particles
In these cases, DAF systems offer better performance and faster separation.
For many industrial wastewater pretreatment systems, DAF is used either before or instead of sedimentation tanks.
Dissolved Air Flotation (DAF) is a highly efficient and reliable technology for removing suspended solids, oil, and grease from industrial wastewater.
Because of its high separation efficiency, compact design, and flexible operation, DAF systems are widely used in many industrial pretreatment processes.
For industries dealing with high suspended solids or oily wastewater, DAF is often one of the most effective solutions available.
Need Help Selecting a DAF System?
If you are planning a wastewater treatment project and need help selecting the right DAF equipment, our engineering team can provide technical support and customized solutions.
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Dissolved Air Flotation (DAF) Systems and how they can improve your wastewater treatment efficiency.