What is a Dissolved Air Flotation (DAF) Unit?
A Dissolved Air Flotation (DAF) unit is an efficient water treatment device primarily used to remove suspended solids (SS), oils, colloidal substances, and other lightweight pollutants from wastewater. Its core principle involves dissolving air into water and then suddenly releasing it to form microbubbles, which attach to contaminants, reducing their density and causing them to float to the surface for separation.
Working Principle
- Air Dissolution System:
Air is forcibly dissolved into recycled water (or raw water) under high pressure (typically 0.3–0.5 MPa), forming saturated dissolved air water. - Release Phase:
The pressurized water passes through a pressure-reducing valve into the flotation tank, where the sudden pressure drop releases air as microbubbles (20–50 microns). - Attachment and Flotation:
The microbubbles adhere to pollutants (e.g., oil droplets, suspended particles), forming "bubble-particle" aggregates that rise rapidly due to their lower density. - Separation:
Floating sludge accumulates on the surface and is removed by a scraper, while clean water exits from the bottom. Some treated water may be recycled back into the dissolution system.
Key Components
- Pressure dissolution tank: Dissolves air under high pressure.
- Release device: Converts dissolved air water into microbubbles.
- Flotation tank: Separation zone where pollutants float.
- Skimmer (scraper): Removes surface sludge.
- Recycle pump: Supplies high-pressure recycled water.
Types of DAF Systems
- Full-flow pressurized: Entire wastewater stream is pressurized (energy-intensive, suitable for small flows).
- Partial recycle: Only part (30–50%) of treated water is recycled for air dissolution (energy-efficient, widely used).
- Vacuum type: Releases bubbles under negative pressure (rarely used).
Applications
- Industrial wastewater: Oil, grease, and colloid removal in petroleum, chemical, food, paper, and textile industries.
- Municipal sewage: Replaces primary sedimentation or aids sludge thickening.
- Drinking water treatment: Algae and color removal.
Advantages
- High removal efficiency (especially for lightweight pollutants).
- Short retention time (15–30 min), compact design.
- Adjustable bubble size for different water qualities.
Due to its high efficiency and flexibility, the DAF unit is widely used in pretreatment or advanced treatment in water and wastewater treatment systems.
Contact us now for a tailored solution.
Julie
Email: sales@filtrationchina.com
Mobile / WA / WeChat: +86 159 2865 0174
