The harvest step — how the float layer thickens at the surface, reaches 3–8% solids, and is removed by mechanical or hydraulic skimming without breaking the float.
The Science Behind Dissolved Air Flotation
The separated solids accumulate as a float layer at the surface. Managing its build-up, solids concentration (typically 3–8%) and removal — by mechanical scraper or hydraulic flooding — is what turns flotation into a continuous process and sets the dryness of the sludge sent downstream.
From rising blanket to skimmed sludge
Rising aggregates consolidate into a coherent surface blanket.
Typically 3–8% — drier than gravity-settled sludge.
A slow flight scraper beaches and pushes float to a collection trough.
Periodic level rise floats the blanket over a weir — no moving parts.
Beach angle and weir set float dryness and capture.
Float passes to screw press, centrifuge or digestion.
| Method | Float solids | Notes |
|---|---|---|
| Mechanical scraper | 4–8% | Drier float; flight/chain scraper |
| Hydraulic flooding | 2–4% | No moving parts; wetter float |
| Combined / dual | 3–6% | Flexibility across loads |
Continue across the DAF science series
The micro-bubble DAF overview and hub.
Read MoreAggregate density and Stokes rise that size the tank.
Read MoreHandling and dewatering the DAF float.
Read MoreEstimate cake dryness and polymer demand.
Read MoreThe packaged DAF unit, sized to your influent.
Read MoreOur process engineers design dissolved air flotation from first principles — float layer & skimming and the full bubble physics — for guaranteed removal at minimum lifecycle cost.
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