CDFU Swirl Dissolved Air Flotation: How Micro-Bubbles Take Over Separation

Why oily wastewater keeps outgrowing conventional treatment

Oil extraction, refining, petrochemicals and machinery manufacturing all produce oily wastewater, and the stream is usually complex and heavily emulsified. Handled badly, it damages water bodies, soil and ecosystems in ways that take years to reverse. Gravity settling, chemical demulsification and conventional flotation are the traditional answers, and each one carries a familiar set of drawbacks: low efficiency, a large footprint, high operating cost, and the chemical sludge and secondary pollution that come with dosing.

The CDFU — the compact swirl dissolved air flotation unit developed by SINOKLE — was built to close that gap. It combines centrifugal separation, dissolved air flotation and ultra-fine bubble generation in a single vessel, which is what allows it to treat difficult oily wastewater in a fraction of the space a conventional dissolved air flotation train occupies.

The mechanism: swirl first, bubbles second

The unit's performance rests on a swirl-field enhanced micro-bubble flotation mechanism, and it operates in three movements.

Swirl pre-concentration

Wastewater enters the vessel tangentially under a specific pressure, generating a high-intensity swirl centrifugal force field. Oil droplets and suspended solids are thrown toward the cylinder wall, where they are enriched and collide with each other. That pre-concentration is what raises the capture probability of the flotation stage that follows; without it, bubbles would simply rise past droplets without meeting them.

Micro-bubble capture

Patented technology generates large numbers of dispersed micro- and nano-scale bubbles. These bubbles present a large specific surface area, a slow rise velocity and high interfacial activity, so they adsorb and envelop droplets and particles that have already coalesced. Slow rise is the counter-intuitive advantage: bubbles that linger have more opportunity to attach.

Separation and discharge

Swirl and buoyancy act together to drive the bubble-droplet complexes into the oil collection zone, where they are discharged continuously by an automatic control system. Purified water leaves from the bottom. The entire physical separation takes place in a sealed, pressurised environment, with a residence time of only one to five minutes and a treatment efficiency five to eight times higher than traditional flotation.

What the process delivers

Reliable effluent. Single-stage de-oiling efficiency exceeds 90%, and the unit reliably removes oil droplets and suspended solids of 2 um or more. Effluent oil and suspended solids contents can each be reduced to 10 mg/L or less, which meets stringent reuse and discharge standards rather than merely scraping past them.

Compact deployment. The standardised skid-mounted design occupies only about 10% of the footprint of traditional dissolved air flotation, and high modularity makes it easy to transport, install and start up. That suits land-constrained plant retrofits, offshore platforms and distributed treatment points, where a conventional train simply will not fit.

Low-carbon operation. Separation is purely physical, with no chemical flocculants required, so oily sludge classed as hazardous waste is avoided at the source and the recovered oil is of high purity. Few rotating devices keep energy consumption down, and automated operation trims labour and maintenance cost.

Tolerance to variation. The process copes with wide swings in influent quality and quantity, and fully enclosed automatic control supports remote monitoring and unattended operation. For a plant that receives variable feed, robustness matters more than peak efficiency, and this is where conventional flotation usually gives way first.

Field results against complex conditions

Two installations illustrate the range. At an oilfield in Africa, a produced water treatment project reached a treatment capacity of 5,000 m3/day, with operating data showing effluent oil content holding steadily at 10 mg/L or below — well inside industry standards — and maintenance cost falling noticeably because the train has so few wearing parts.

At an oilfield in Xinjiang, China, CDFU serves as the core process treating produced water with high-concentration influent. The system demonstrated strong shock resistance and stability, with effluent quality that has supported the field's continuous production. Handling high-concentration feed without a stability drop is the case that separates a workable process from a promising one.

The economics reinforce the same conclusion. With no flocculant purchases, no oily sludge classified as hazardous waste and a far smaller equipment footprint, the cost of treating a cubic metre of oily water falls on every line of the budget rather than only on the capital line. That is what makes a compact physical unit attractive even where the influent is not especially difficult, because the saving compounds over the life of the plant rather than being booked once at commissioning.

From end-of-pipe treatment to in-process cleanliness

Against the broader push toward green, low-carbon operation, clean production in the oil industry is no longer optional. The significance of CDFU lies in more than providing an efficient device. By following a purely physical, zero-chemical, high-efficiency and low-energy path, it shifts oilfield production from treating pollution at the outlet toward keeping the process clean in the first place. Resource recovery of waste oil and reduced operating cost then turn environmental compliance into something with a measurable return, which is the only kind of green investment that survives budget cycles.