Dissolved Air Flotation (DAF), Induced Gas/Air Flotation (IGF/IAF) and Dissolved Gas Flotation (DGF) all float contaminants to the surface with rising bubbles — but they make those bubbles in very different ways, and that one difference decides which is right for your water. This is the engineering comparison, from a builder of both.
The whole comparison comes down to how the bubble is generated. Dissolved-type units (DAF, DGF) saturate water with gas under pressure and release it to nucleate very fine bubbles; induced-type units (IGF/IAF) shear gas into the water mechanically, making coarser bubbles. Fine bubbles give the highest clarity on light, flocculated solids; coarse bubbles are robust and compact for heavy free-oil duties. Everything else — energy, footprint, retention time, target contaminant — follows from that.
The three flotation families compared
| Parameter | DAF (Dissolved Air) | IGF / IAF (Induced Gas/Air) | DGF (Dissolved Gas) |
|---|---|---|---|
| Bubble generation | Air dissolved in pressurised recycle (4–6 bar) then released | Gas sheared in mechanically (impeller, eductor, sparger) | Inert gas dissolved under pressure then released (DAF principle, gas instead of air) |
| Bubble size | Fine, 30–50 micron | Coarse, ~100–1,000 micron | Fine, 30–50 micron |
| Best for | Low-density solids, algae, FOG, light flocs, fibres | High free-oil loads, robust/dirty duties | Oily water where air is unsafe (hydrocarbons, anoxic) |
| Retention time | Moderate (lamella-aided, compact) | Short per cell, usually multi-cell | Moderate |
| Energy | Moderate (saturator + recycle pump) | Low–moderate (mechanical aerators) | Moderate + gas supply |
| Clarity / fine solids | Highest | Lower (coarse bubbles) | High |
| Typical sectors | Municipal, food & beverage, industrial, desalination pre-treatment | Refinery, petrochemical, produced water | Offshore oil & gas, hazardous/inert-blanketed service |
DAF saturates a recycle stream with air at 4–6 bar in a saturator vessel; when that water is released back into the flotation cell, the sudden pressure drop nucleates a cloud of 30–50 micron micro-bubbles (Henry’s law in reverse). Those fine bubbles attach to coagulated/flocculated particles and lift them to the surface as a float, which a skimmer removes. The fineness of the bubbles is the point: it gives the highest clarity and is unbeatable on low-density solids — algae, fats/oils/grease, protein, fibres and light chemical flocs.
It is the default choice for municipal clarification, food-and-beverage effluent, and as seawater RO pre-treatment (algae and TEP removal). DAF needs coagulation/flocculation upstream and a saturator + recycle pump, so it carries a little more mechanical complexity than induced units — repaid in effluent quality and a small footprint (especially lamella-aided).
IGF makes bubbles mechanically — a rotating impeller, eductor or sparger shears gas directly into the water — producing much coarser bubbles (~100–1,000 micron). The result is a rugged, compact, usually multi-cell unit with short per-cell retention. It tolerates high and variable free-oil loads that would overwhelm a fine-bubble DAF, which is why it dominates refinery and produced-water de-oiling. The trade-off is lower polishing clarity on fine solids: coarse bubbles don’t capture the smallest particles as efficiently. (IAF is simply the air-driven version; IGF the general gas term.)
DGF works exactly like DAF — dissolve gas under pressure, release to nucleate fine bubbles — but uses an inert gas (nitrogen or fuel gas) instead of air. That matters wherever introducing oxygen is unsafe or undesirable: hydrocarbon streams, offshore platforms and explosive/anoxic service, where an air blanket would create an ignition risk or oxidise the process. You get DAF-grade fine-bubble clarity with gas compatibility, at the cost of a gas supply and blanketing system. Offshore produced-water packages are frequently DGF or gas-blanketed IGF for exactly this reason.
Start from the contaminant and the environment
| If your priority is… | Choose |
|---|---|
| Highest clarity on fine/light solids, algae, FOG | DAF |
| Seawater RO pre-treatment (algae, TEP) | DAF |
| High, variable free-oil loads (refinery, petrochem) | IGF / IAF |
| Compact, robust, tolerant of upsets | IGF / IAF |
| Oily water where air is unsafe (offshore, hydrocarbons) | DGF (or gas-blanketed IGF) |
| Fine-bubble clarity and an inert atmosphere | DGF |
Send us the contaminant, the loads and the environment — our engineers will recommend DAF, IGF or DGF, size it, and (where useful) pilot it on your actual water before you commit.
Flotation technology, sizing and applications
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