Pressurised recycle flow dissolves air into treated water, which is then released at atmospheric pressure to create the flotation bubble blanket.
Free interactive DAF sizing calculator. Calculate dissolved air flotation surface area, recycle flow, saturator volume, and power.
FOG removal food industry DAF systems for fat oil grease recovery food processing.
DAF systems for oil and gas produced water and refinery wastewater treatment.
Design DAF systems for correct hydraulic loading. Surface area, rise rate and detention time calculations for your flow.
A portion of treated effluent is pressurised and saturated with air in the air dissolution tank.
The pressurised water is released through a pressure reduction valve into the flotation zone.
As pressure drops, dissolved air comes out of solution, forming micro-bubbles throughout the water.
Typically 10-30% of influent flow is recycled, adjustable based on treatment requirements.
Uses treated water for air dissolution, reducing pumping requirements and energy consumption.
Recycle rate can be optimised for different influent conditions and treatment goals.
Using treated water ensures consistent air saturation and bubble formation.
Proven technology with straightforward operation and minimal maintenance requirements.
Dissolved Air Flotation is a physico-chemical separation process that removes suspended solids, oils, greases, and colloidal matter from wastewater. Pressurised water saturated with air is released into the flotation zone, generating microbubbles that attach to flocculated particles and float them to the surface as a concentrated sludge blanket. The clarified water exits below the floating sludge layer.
Recycle stream pressurised to 4-6 bar in a saturation vessel with optimised retention time.
Pressure release through proprietary nozzles generates 20-80 µm bubbles with high attachment efficiency.
Rising velocity of bubble-particle agglomerates exceeds settling velocity, forcing separation.
Mechanical scrapers or hydraulic suction systems continuously remove concentrated float.
| Hydraulic Loading | 5 – 15 m³/m²/h |
| Solids Loading | Up to 15 kg SS/m²/h |
| Air-to-Solids Ratio | 0.02 – 0.1 kg air/kg SS |
| Recycle Ratio | 10 – 50% of influent flow |
| Flotation Zone Depth | 1.5 – 3.0 metres |
| Retention Time | 10 – 30 minutes |
| Drive Power | 0.37 – 2.2 kW (scraper mechanism) |
| Construction | SS304, SS316L, or carbon steel with epoxy coating |
95 – 99% suspended solids reduction depending on flocculant selection and upstream conditioning.
>98% oil and grease removal for emulsified and free-floating hydrocarbons.
40 – 70% COD removal depending on solids fraction and coagulant optimisation.
Complete dissolved air flotation systems for industrial and municipal applications.
View PageThe recycle stream carries the bubble payload that drives flotation. Right-sizing matters.
A portion of clarified effluent is pressurised, saturated with air at 4–6 bar, then released back into the inlet to create microbubbles. This is the standard pressurised-recycle DAF configuration.
Recycle as % of forward flow: 15–50% typical. Low-A/S duties: 15–25%. High-A/S oily duties: 35–50%. Higher recycle → more bubbles but more dilution.
A/S = (air solubility × recycle ratio × saturator efficiency) / influent solids concentration. Solve for recycle ratio given target A/S.
Higher pressure (8–10 bar) lifts air solubility, reduces recycle ratio. Useful when influent solids are very high. Trade-off: higher pump energy, more demanding pressure vessel.
Centrifugal multistage for 4–6 bar saturator; high-pressure positive-displacement for 8+ bar. NPSHa > 3 m at pump inlet. VFD allows recycle-ratio tuning.
Specific orifice or check valve at recycle injection creates the pressure drop that nucleates microbubbles. Wear-resistant materials (tungsten carbide) for long life.
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