Calcium-carbonate and struvite scale builds on saturator packing, release nozzles, and tank internals — throttling air, distorting bubbles, and cutting performance. This guide covers scale chemistry and how to keep internals clean.
Recognise the problem fast, then work through the causes and solutions below.
What you see: Hard scale on nozzles and packing in hard-water or lime-dosed plants reduces air dissolution and blocks orifices.
What you see: Struvite (Mg-ammonium-phosphate) forms on internals in nutrient-rich feeds (digestate, food/dairy), especially at higher pH.
What you see: Patchy white-water and rising saturator ΔP as orifices and packing voids clog.
| Check | Target / Action | Typical value |
|---|---|---|
| Feed hardness/alkalinity | Set descale frequency | Site-specific |
| Coagulation pH | Avoid carbonate precip. | 6.0–7.5 |
| Descale agent | Acid clean | ~5% citric acid |
| Saturator ΔP | Trend & trigger clean | Rising = fouling |
| Recycle source | Cleanest point + strainer | Low solids |
Set up correctly, dissolved air flotation turns this failure mode into a controllable, high-performance process.
DAF nozzles, packing and weirs are designed for inspection and acid cleaning, so scale is managed on a planned cycle rather than as a failure.
Because coagulation pH is actively controlled, the operating window can be kept below the carbonate-precipitation threshold while still flocculating well.
Drawing recycle from clarified effluent and straining it keeps the most scale-sensitive component — the saturator — clean.
Saturator pressure drop and bubble quality give early, measurable warning of scaling long before clarification suffers.
NPSH, air ingress, and impeller wear that destabilise the recycle.
Cutting saturator, recycle, and air-system energy without losing performance.
Viscosity, gas solubility, and freezing effects on winter flotation.
Safe sequencing, priming, and stagnation control around stop/start.
Emulsified oil, FOG breakthrough, and demulsification chemistry.
Diurnal swings, batch dumps, and shock loads that destabilise the cell.
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