Hydrogen-sulphide odour and a dark, gassy float blanket signal anaerobic activity in or upstream of the DAF. This guide covers septic feed, float decomposition, and how prompt flotation keeps the process aerobic.
Recognise the problem fast, then work through the causes and solutions below.
What you see: Feed is already anaerobic from long sewers or balancing tanks; the DAF cannot fix upstream septicity alone.
What you see: Float left too long turns anaerobic, generates gas, rises, and re-entrains — releasing odour.
What you see: Odour traced to scum lines, hoppers, or downstream holding rather than the cell surface.
| Check | Target / Action | Typical value |
|---|---|---|
| Float residence | Skim before it turns | <4 hours |
| Upstream balance | Aerate / turn over | Avoid stagnation |
| Sulphide control | Nitrate / oxidant dosing | To suppress H₂S |
| Scum lines | Flush, no dead legs | Routine cycle |
| Vent odour | Biofilter / carbon | Sensitive sites |
Set up correctly, dissolved air flotation turns this failure mode into a controllable, high-performance process.
DAF removes solids fast and, when skimmed promptly, keeps the float fresh and aerobic — the surest defence against odour.
Pulling BOD-rich solids out quickly reduces the substrate available for sulphate-reducing bacteria downstream.
Variable-speed skimming clears the blanket before decomposition starts, so gas generation and re-entrainment never get going.
DAF units can be covered and vented to odour control, containing any residual odour at source for sensitive locations.
Calcium-carbonate and struvite scale on nozzles, packing, and internals.
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.
Our process engineers diagnose and resolve complex DAF performance issues on site or remotely — from chemistry and air systems to hydraulics and sludge handling.
Our expertise spans multiple industries with sector-specific water treatment solutions.