How a Dissolved Air Flotation (DAF) System Works for Wastewater
Sep 14, 2026
How a Dissolved Air Flotation (DAF) System Works for Wastewater
First and foremost, a Dissolved Air Flotation (DAF) system is a highly efficient water clarification technology. Its primary purpose is to separate suspended solids (TSS), fats, oils, grease (FOG), and other low-density particles from a liquid stream.
In essence, a DAF system is an important part of many Wastewater Treatment Plant (WWTP) pretreatment stages. It tackles problematic contaminants such as high TSS levels and fats, oils, and grease (FOG) at an early stage.
By removing these pollutants early, a DAF system can significantly reduce the load on downstream biological treatment processes, help optimize chemical consumption, and improve the overall performance of the wastewater treatment process.
The DAF process can be broken down into four essential stages:
⚙️ 1. Chemical Coagulation and Flocculation (Pretreatment)
Before the wastewater enters the main DAF tank, coagulants such as aluminum or iron salts and flocculants such as polyelectrolytes are typically added.
These chemicals neutralize electrical charges and cause fine suspended particles and colloidal matter to bind together, forming larger, fluffy agglomerates called “flocs.”
This step is crucial because larger flocs are much easier for the microbubbles to attach to during the flotation process.
💨 2. Dissolution and Release of Air (Bubble Generation)
This is the heart of the DAF system — creating a large number of extremely fine bubbles.
Dissolution (Pressurization)
A portion of the clarified effluent or clean water is diverted into a pressure vessel called the saturation tank or air-dissolving tube.
Compressed air is injected into this stream under pressure, typically around 4–6 bar. At this elevated pressure, a significant amount of air dissolves into the water, forming a pressurized, air-rich solution.
Release (Depressurization)
The pressurized, air-rich water is then discharged through special pressure-release nozzles into the main DAF flotation tank, which is normally at atmospheric pressure.
The sudden pressure drop causes the dissolved air to come out of solution and form a large number of microscopic bubbles, typically around 20–40 micrometres in diameter.
These microbubbles provide the flotation force required for efficient solid-liquid separation.
⬆️ 3. Bubble Attachment and Flotation (Separation)
In the contact zone of the DAF tank, the released microbubbles mix with the chemically pretreated wastewater.
The microbubbles attach to the surfaces of flocs, oil droplets, and other suspended particles. Once attached, the overall density of the bubble-particle agglomerates becomes lower than that of water, causing them to rise to the surface under buoyancy.
This creates a floating layer of sludge, commonly called the “float” or “scum,” on the surface of the DAF tank.
At the same time, the clarified water remains below the floating layer and moves toward the treated-water collection area.
🧹 4. Sludge Skimming and Collection (Final Clarification)
Sludge Skimming
The accumulated floating sludge layer is continuously or intermittently removed from the surface by chain-driven or spiral skimmers.
The collected sludge is directed into a sludge trough and can then be sent for further sludge dewatering, treatment, or disposal, depending on the project requirements.
Clear Effluent Withdrawal
The clarified water remains in the lower portion of the flotation tank. It is collected uniformly through a system of collection pipes or launders and discharged from the DAF unit.
Depending on the overall treatment process, the clarified effluent can then proceed to biological treatment, MBR, UF, RO, or other downstream treatment processes, or be reused when the required water quality is achieved.
💡 Key Advantages and Typical Applications
DAF is especially effective for contaminants whose density is close to or less than that of water, including:
Fats, oils, and grease (FOG)
Suspended and colloidal solids
Algae and fibers
Emulsified oils
Other low-density particles
With appropriate chemical conditioning and proper system design, DAF can achieve high removal efficiency. Actual performance depends on wastewater characteristics, chemical dosage, hydraulic loading, air-to-solids ratio, and overall process design.
Common Applications Include:
Industrial wastewater – food processing, dairy, meat processing, pulp and paper, petrochemical, and metal finishing industries.
Municipal wastewater – as a primary treatment step or for sludge thickening.
Drinking water treatment – for removing algae, turbidity, and other suspended particles.
Oil-water separation – for applications such as refinery and marine wastewater treatment.
In summary, a Dissolved Air Flotation (DAF) system combines chemical conditioning, pressure-dissolved air, and physical flotation to provide a robust and widely adaptable solution for solid-liquid separation in wastewater treatment.
The effectiveness of DAF makes it an important pretreatment technology for many industrial wastewater treatment applications, particularly where high levels of TSS, oil, grease, and floating or colloidal solids need to be removed before downstream treatment.
DAF Wastewater Treatment Solutions from Hinada
At Hinada Water Treatment Tech Co., Ltd., we are more than just an equipment supplier. We provide water and wastewater treatment solutions based on each customer's specific water quality, treatment capacity, and project requirements.
Our DAF systems can be integrated with other wastewater treatment technologies, including MBR membranes, UF systems, RO systems, sludge dewatering, and packaged wastewater treatment systems, to create a complete and efficient treatment process.
With expertise in wastewater treatment equipment and membrane technologies, Hinada supports customers from process design and equipment manufacturing to installation and commissioning, providing practical solutions for industrial and municipal wastewater treatment projects.
To discuss how a DAF system can be integrated into your wastewater treatment process, contact the Hinada team to discuss your project requirements.
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