DAF retrofit
The basin is fine. The bubbles are not.
Most flotation plants that underperform do not need new civil works. They need a different gas source. The distinction matters because it is the difference between a three-day job and a six-week one.
Four symptoms of an ageing DAF
- The recycle ratio keeps climbing. It started at 20% and someone has pushed it to 30% or more to hold the effluent. That is a symptom of lost dissolution efficiency, not of insufficient flow.
- Release nozzles block. Every blockage is a local dead zone, and the fix — cleaning nozzles — is labour that never appears in the operating budget.
- Fine particles pass through. Conventional 20–100 µm bubbles collide poorly with particles below 10 µm and with emulsified oil. The unit is working exactly as designed; the design has a floor.
- Sludge is watery. A broken float layer carries water with it, so haulage volumes rise even when the dry solids captured are unchanged.
Three tiers, priced in downtime as well as capital
| Tier | What changes | What stays | Window | Expected outcome |
|---|---|---|---|---|
| 1 · Gas source | Nanobubble generator replaces the release system | Tank, scrapers, civil works, pipework | ≈3 days | Bubble size down two orders of magnitude; chemical dosing typically 30–50% lower |
| 2 · Contact zone | Tier 1 plus staged injection manifold and revised contact zone | Tank and scrapers | 1–2 weeks | TSS removal into the 90%+ band on suitable feed |
| 3 · New skid | Complete ARFU unit, old basin decommissioned or kept as buffer | Site, permits, discharge point | 4–6 weeks | 94% TSS, 0.18 kWh/m³, 50% footprint |
Measure these five things before you choose a tier
- Inlet and outlet TSS, with the sampling point and time of day. A single grab sample is not a baseline.
- Recycle ratio and dissolution pressure. If the pressure has been raised to compensate, the release system is the problem.
- Particle size distribution of the feed. Below 10 µm, a conventional unit will always struggle; that is the strongest argument for Tier 2 or 3.
- Float dry-solids content and haulage cost. Sometimes the payback is in sludge volume, not in effluent quality.
- Available footprint and isolation capability. A single-train plant with no bypass needs a longer window than the table above, and that changes the recommendation.
What a retrofit will not do
Keep these expectations honest
- It will not fix short-circuiting. If the basin has dead zones or a broken baffle, a better bubble just takes a different path through them.
- It will not remove dissolved oil. Flotation lifts free and dispersed oil. Dissolved oil needs oxidation or biological treatment.
- It will not double capacity. Expect 10–30% more hydraulic throughput at equal effluent quality on a well-designed basin; the larger gains come from chemical and sludge savings.
- It will not work without pre-screening. Rags and grit destroy nozzles faster than they destroy pumps.
Reference: Cui Jiagou mine water 2×75 m³/h, flotation + 20 nm SiC, accepted at 0.18 NTU and 94% TSS; 500 t/h nanobubble flotation system at 99.8% TSS removal on a high-solids feed. Both are new-build and retrofit references respectively; we will name which applies to your site once we have seen the basin.
Send three photographs: the basin, the release header, the float
Plus the last twelve months of effluent data. That is usually enough to say which tier applies — and whether a retrofit is worth doing at all.
Start a retrofit review → How ARFU works