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DAF Cold-Weather Operation

Low temperature changes water viscosity, gas solubility, and reaction rates — and brings a freezing risk to exposed units. This guide covers winter performance shifts and how to keep flotation reliable in the cold.

Symptoms You’ll See

Recognise the problem fast, then work through the causes and solutions below.

Slower, weaker floc in winter Reduced rise velocity / thinner float Higher coagulant demand Freezing on exposed pipework Instrument lines freezing

Higher viscosity slows flotation

What you see: Cold water is more viscous, so bubbles and flocs rise more slowly and the effective loading rate falls.

Likely Causes & Solutions

  • Bubble rise slowed by viscosity: Modestly increase recycle/air to compensate, and avoid running at the top of the loading band in winter.
  • Floc settling/rising slower: Lengthen flocculation slightly and confirm float quality; do not overload the cell.
  • Loading at summer design in winter: De-rate throughput in the coldest months if effluent quality drifts.

Coagulation chemistry shifts with temperature

What you see: Reaction and hydrolysis rates fall; the warm-weather dose and pH may no longer be optimal.

Likely Causes & Solutions

  • Higher coagulant demand: Re-run jar tests at winter temperature and re-set dose/pH for the season.
  • Slower polymer activation: Allow longer polymer make-down/ageing; confirm it is fully activated before dosing.
  • Fixed seasonal set-points: Adjust SCADA set-points seasonally rather than leaving summer values.

Freezing risk on exposed plant

What you see: Outdoor pipework, dosing lines, and instrument tubing can freeze, causing blockages and false readings.

Likely Causes & Solutions

  • Exposed pipework freezing: Trace-heat and insulate vulnerable lines (recycle, dosing, instrument tubing).
  • Stagnant lines freezing: Keep flow in lines or provide drain-down for shutdowns in hard frost.
  • Frozen instrument tappings: Heat-trace impulse lines so pressure/level instruments stay live.

Cold-weather checklist

CheckTarget / ActionTypical value
Loading rateDe-rate if neededLower in coldest months
Recycle/airCompensate for viscosityModest increase
Coagulant doseRe-jar-test seasonallyWinter optimum
PipeworkTrace-heat & insulateRecycle, dosing, instruments
Set-pointsAdjust seasonallyNot fixed summer values

How DAF Solves It Effectively

Set up correctly, dissolved air flotation turns this failure mode into a controllable, high-performance process.

Compensate without rebuilds

Because air and recycle are adjustable, the viscosity penalty of cold water is offset with control changes, not new equipment.

Re-tunable chemistry

Seasonal jar testing keeps coagulation optimal year-round, so winter flocs stay strong and liftable.

Enclosable & heat-traceable

DAF units can be housed or trace-heated, making reliable cold-climate and outdoor operation straightforward.

Predictable physics

The temperature effects on gas solubility and viscosity are well understood, so winter de-rating can be planned rather than discovered.

↓ riseCold = slower flotation
SeasonalRe-jar-test
Trace-heatFreeze protection
De-rateColdest months

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