Conventional DAF or CDFU? A Side-by-Side Comparison Backed by Five Operating Cases

The word flotation covers a wide range of equipment, and the gap between one system and another is larger than most procurement documents acknowledge. Conventional dissolved air flotation (DAF) has been in service for decades and has genuine strengths, but it also carries familiar pain points: long retention time, large footprint, high chemical consumption and oil-removal efficiency that moves around with influent quality. The CDFU (Cyclonic Dissolved Gas Flotation Unit) independently developed by SINOKLE takes a different route through patented technology. What follows is a direct comparison rather than a narrative.

What the CDFU actually is

The CDFU (Cyclonic Dissolved Gas Flotation Unit) cyclonic dissolved air flotation device is a new-generation, high-efficiency, compact, sealed and pressurised flotation system built on SINOKLE patented technology and first of its kind in China. It combines cyclonic centrifugal separation, micro-bubble generation and dissolved air flotation in one vessel, and the combination is what achieves fast separation of waste oil, emulsified oil and suspended solids.

The working principle is geometric. Micro-bubbles of 5–30 µm mix with the wastewater and enter a cyclonic flow. Centrifugal force drives the bubbles and oil droplets toward the centre, where they coalesce into scum and are discharged with nitrogen from the oil outlet, while cleaned water leaves from the bottom outlet. Because the separation happens along a radial path rather than by gravity settling through a deep tank, the vessel can be small and the residence time short.

Head to head, aspect by aspect

• Retention time. Conventional DAF runs 15–40 min; the CDFU holds under 5 min, only 1/8 to 1/3 of conventional. That ratio translates almost directly into tank volume.
• Single-stage oil removal. Conventional DAF achieves 60%–85%; the CDFU achieves over 90%.
• Single-stage suspended-solids removal. 50%–70% for conventional DAF against over 80% for the CDFU.
• Removable particle size. Conventional DAF handles particles larger than 5 µm; the CDFU reaches below 3 µm, a clear advantage for fine particles and emulsified oil.
• Bubble quality. Conventional systems produce 5–100 µm bubbles with average uniformity; the CDFU produces 5–30 µm bubbles of good uniformity. Uniformity, not the mean, is what makes capture predictable.
• Operation and sludge discharge. Conventional DAF is manual and open, with a mechanical scraper; the CDFU is automatic, enclosed and pressure-driven, with no mechanical power and no on-site oil-gas leakage.
• Structure and footprint. Conventional DAF needs reinforced-concrete civil works and a long lead time; the CDFU is a pressure-vessel skid, factory-prefabricated, at only 1/3 the footprint.
• Energy and chemical use. The CDFU uses only 10% of the energy of conventional IGF, with gas at 1%–3% of throughput, low chemical and sludge demand, and tolerance of 10%–120% flow variation.

Five cases that test the claims

Oil-depot draw-off water

A CDFU combined with a KHC coalescing oil remover forms a purely physical process with fully enclosed operation, off-gas routed to the oil-gas recovery system, and recovery of high-quality light oil for direct reuse. The configuration is widely used in tank farms of CNPC, Sinopec and China Power.

Treatment plant flotation upgrade

A two-stage CDFU scheme was adopted: the first stage performs purely physical demulsification with oil recovery and no hazardous waste, and the second stage needs only a small dose of PAC. Effluent oil and suspended solids both come in at or below 20 mg/L.

Oily fire-fighting wastewater

Here a CDFU and MACT combination reached oil removal of 90% or more and withstood 10%–120% flow fluctuation, which is what makes skid-mounted rapid emergency treatment practical — the load arrives without warning and cannot be paced.

Fracturing flowback fluid

The train runs CDOF gel-breaking and viscosity reduction, then CDFU high-efficiency oil and solids removal, then fine filtration. Skid equipment can be vehicle-mounted for on-site operation, and the filtered water meets reuse standards.

Pharmaceutical wastewater

Upstream CDFU with 5–20 µm ultra-fine bubbles achieved SS removal above 95% and extended catalyst life by more than 30%; a pilot at a large Inner Mongolia pharmaceutical group succeeded.

What the comparison really shows

Behind the table sits a divergence of two technological routes. Conventional flotation seeks balance in "big tanks plus long retention" — a reasonable answer when land is cheap and influent is predictable. The CDFU re-engineers efficiency with cyclonic flow and micro-bubbles, which pays off where space is tight or where influent moves. For a new project, skid-mounting means faster construction and fewer civil interfaces. For a retrofit, it means fitting into a footprint the existing building can accommodate. For the operator, it means less chemical and simpler maintenance.

One practical note on retrofits: many WWTP upgrades are driven by a flotation cell that has become the hydraulic bottleneck rather than by a change in influent quality. In that situation the comparison above is beside the point until the bottleneck is identified, because replacing a cell with a faster unit only moves the constraint to the next vessel. Measure the residence time of the downstream stages before sizing the flotation replacement.

When conventional DAF is still the right answer

Honesty matters more than advocacy here. Where the stream is large, the oil is mostly free rather than emulsified, land is available and chemical dosing is not a major cost line, a conventional DAF will meet the requirement at lower capital. The CDFU's advantages concentrate in emulsified oil, fine solids, tight footprints, fluctuating loads and enclosed handling where vapour release is unacceptable. Test a representative sample before committing either way, and specify the removal figure at the particle size that actually appears in the feed rather than the one in the brochure.