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Lab-to-decision summary
- Label Value
- --- ---
- Best first test Jar test with parallel flotation and settling observation
- Key density threshold About 1.02–1.05 g/cm³ for borderline solids
- Typical DAF surface loading 3–8 m/h
- Typical lamella equivalent loading 1–3 m/h
- DAF tends to fit Light, oily, filamentous, variable solids
- Lamella tends to fit Denser, more stable, readily settling solids
- Commissioning focus Reagent trim, recycle pressure, sludge handling, solids capture
What the jar test should reveal
A useful jar test does not just show whether solids separate. It should show how fast they separate, whether the floc remains intact, and whether the separated phase is a skim, a sludge, or a mixed layer. If the sample forms buoyant, oily, or flaky agglomerates that rise cleanly, flotation is usually favored. If it forms dense, compact aggregates with a clear settling front, sedimentation is usually favored.
Jar test and selection workflow
- Collect representative samples across normal and peak conditions.
- Run coagulant and flocculant dosage screening before the separation test.
- Observe settling and flotation behavior in parallel.
- Measure or estimate particle density for the solids fraction.
- Compare results against the 1.02–1.05 g/cm³ decision zone.
- Map the expected hydraulic loading to DAF or lamella operating ranges.
- Select the technology with the wider stable operating window.
- Commission with stepwise chemical and hydraulic optimization.
Why is the density range around 1.02–1.05 g/cm³ so important?+
It is a borderline zone where solids may neither settle cleanly nor float reliably. Small changes in chemistry, floc structure, or entrained air can strongly affect the outcome.
Can a jar test alone decide between DAF and lamella settling?+
It is a strong first filter, but not enough by itself. Particle density, variability, hydraulic loading, and commissioning behavior should confirm the choice.
What is the most common commissioning mistake after choosing DAF?+
Overdosing chemicals too early. That can create bulky, water-rich sludge and reduce separation efficiency, so dosage should be trimmed gradually.
Equipment we supply for this
Engineering Hub: get this sized for your plant
Describe your goal, effluent limit or sludge volume and receive a technology shortlist plus a sizing proposal – by email, no phone call required.