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What is Dissolved Air Flotation?
Dissolved Air Flotation (DAF) is a physico-chemical separation process used for the removal of suspended solids, oils, fats, and other light contaminants from wastewater.
Principle of Operation
A partial stream of the treated water is saturated with air under pressure (4-6 bar). When this recycle stream is depressurised, microbubbles measuring 20–40 µm in diameter are released. These fine bubbles attach themselves to aggregates previously formed by coagulation and flocculation, lifting them to the surface of the water.
Pre-treatment
Appropriate pre-treatment is essential for optimal performance:
- Coagulation: Addition of metal salts (e.g. ferric chloride, PAC) to destabilise colloidal particles
- Flocculation: Addition of polymer to form larger flocs
- pH Adjustment: Setting the optimal pH for coagulation
Typical Performance Data
- Fat/oil removal: >95%
- TSS removal: >95%
- Phosphorus removal: >90% (with precipitation)
- COD reduction: 60–85%
Fields of Application
DAF units are deployed across numerous industries:
- Food and beverage industry
- Abattoirs and meat processing
- Petrochemical and refinery sector
- Metal processing industries
- Pre-treatment prior to biological treatment stage