Dissolved air flotation (DAF) downstream of an MBBR floats biofilm-origin suspended solids to the surface using micro-bubbles, then skims them off. DAF can handle the lighter, finer solids that MBBR produces better than gravity settling, making it a strong alternative to the secondary clarifier — especially for compact plants and industrial applications.
Why DAF works well after MBBR
MBBR effluent solids are often smaller and less dense than activated-sludge flocs, which makes gravity settling slower. DAF reverses the separation mechanism: micro-bubbles attach to the particles and lift them to the surface, regardless of particle density. This gives reliable removal even for the light, irregular biofilm fragments that a gravity clarifier struggles with.
DAF units also have a much smaller footprint than gravity clarifiers for the same duty, which suits compact or modular plants. Coagulant and polymer dosing ahead of the DAF typically improves performance. The floated sludge is collected as a concentrated float and dewatered separately.
Design factors
Downstream DAF after MBBR (indicative — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Separation | Flotation (micro-bubbles) | — | Effective for light biofilm solids. |
| Footprint | Smaller than clarifier | — | Good for compact/modular plants. |
| Chemistry | Coagulant + polymer | — | Usually dosed ahead of DAF. |
| Sludge | Concentrated float | — | Collected and dewatered separately. |
Frequently Asked Questions
When should I use DAF instead of a clarifier after MBBR?
Does DAF need chemical dosing?
Can DAF replace the secondary clarifier entirely?
Related Pages
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