The chemistry that makes flotation work — coagulants (ferric, alum, PAC), flocculant polymers, charge neutralisation and zeta potential, plus coagulant-free operation.
The Science Behind Dissolved Air Flotation
Most DAF duties are conditioned chemically: a coagulant (ferric, alum or PAC) neutralises particle charge and a polymer flocculates the destabilised solids into larger, more hydrophobic, more floatable aggregates. This page covers coagulant selection, dosing, zeta potential, jar testing and when DAF can run coagulant-free.
Destabilise, flocculate, float
Coagulants collapse the electrical double layer so particles aggregate.
Ferric chloride/sulphate, alum and PAC — chosen by pH and floc.
High-MW polymers bridge particles into large, floatable flocs.
Dosing to near-zero zeta gives the best aggregation.
Bench jar tests set coagulant, polymer and pH before scale-up.
High-FOG streams can float on air alone with little or no chemical.
| Chemical | Typical dose | Role |
|---|---|---|
| Ferric chloride | 50–200 mg/L | Coagulation, P removal |
| Alum | 50–150 mg/L | Coagulation |
| PAC (polyaluminium) | 20–100 mg/L | Coagulation, wide pH |
| Polymer (flocculant) | 0.5–5 mg/L | Floc growth |
| Acid / alkali | to optimal pH | Coagulation window |
Continue across the DAF science series
The micro-bubble DAF overview and hub.
Read MoreCollision and attachment mechanics that capture particles.
Read MoreCoagulant and polymer dosing for DAF.
Read MoreEstimate coagulant and polymer demand.
Read MoreWhat DAF removes and how well - TSS, FOG, P, metals, algae.
Read MoreOur process engineers design dissolved air flotation from first principles — coagulation chemistry and the full bubble physics — for guaranteed removal at minimum lifecycle cost.
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