When suspended solids, oil or grease are the problem, the choice usually comes down to a dissolved air flotation unit or a settling tank. Both clarify water; they just push the dirt in opposite directions. Here is how to decide which belongs in your plant.
How Each One Works
Sedimentation lets particles denser than water sink under gravity — slow, simple, no moving parts beyond a scraper. DAF dissolves air into a pressurized recycle stream and releases it as micro-bubbles that attach to flocs and float them to the surface, where a chain scraper skims the sludge blanket off.
Choose DAF When…
- The dirt floats or barely sinks: fats and oils, grease, algae, fibers, flotables from food, slaughterhouse, dairy, car-wash and textile effluent.
- Space is tight: DAF clarifies at 5–10× the surface loading of a settler, so the footprint shrinks accordingly.
- You want drier sludge: a floated blanket skims off at 2–4% solids, versus watery underflow from many settlers.
- Loads swing: with coagulant dosing ahead, DAF rides shock loads that would blow solids over a settler weir.
Choose Sedimentation When…
- Particles are heavy: grit, metal hydroxide flocs after precipitation, mineral solids — gravity is free and reliable.
- Power must stay minimal: a settler has no saturation pump running around the clock.
- Flows are large and steady: at municipal scale, big clarifiers stay hard to beat on cost per cubic meter.
The Numbers That Decide It
Send a one-liter sample to any local lab and get SS, oil & grease, and COD. As a rule of thumb from our quoting desk: oil & grease above ~50 mg/L or SS dominated by light organics points to DAF; dense inorganic solids point to settling; and many plants sensibly run both — DAF for the greasy stream, a settler after chemical precipitation.
Email the analysis to jinhaofeng298@163.com and we will size the unit, the dosing that feeds it, and the sludge handling behind it — as one quoted package.