Flotation technology works by dispersing highly dispersed microbubbles into water so that the bubbles attach to or envelop suspended particles, forming a gas-liquid-solid three-phase system and achieving solid-liquid or liquid-liquid separation through density differences.
Dissolved air flotation (DAF) is an important branch: air is dissolved in water under high pressure to saturation, and microbubbles of 10~100 μm are released when the pressure drops sharply. The technology involves four core processes — coagulation-flocculation, gas dissolving and releasing, bubble-floc contact, and aggregate separation — corresponding to the coagulation-flocculation system, the dissolve-release system, and the contact and separation zones of the flotation tank.
Based on the centrifugal separation principle, the cyclonic dissolved air flotation unit (CDFU) innovatively couples the centrifugal force field with the flotation process. Pressurized water flows through an ejector, creating negative pressure that draws in gas; the high-speed water shears and mixes with the gas to generate fine bubbles, and the centrifugal field drives floc particles/oil droplets and bubbles to move radially inward toward the center. Compared with conventional flotation, bubbles and flocs/oil droplets in this unit escape streamline constraints by inertia, so collision and attachment are more orderly, greatly intensifying separation.
CDFU delivers significant core advantages: first, the high-efficiency ejector and ultrafine nano-bubble technology ensure thorough mixing of bubbles with wastewater without breaking flocs, with a simple equipment structure, low power demand, and fully closed operation; second, the cyclonic pressurized DAF tank generates a large number of stable microbubbles, and by extending gas-liquid contact time, enlarging oil droplet diameter, reducing bubble size, and increasing bubble concentration, it significantly raises collision probability and attachment efficiency, intensifying oil removal. The unit also has three notable features: eliminating the dead ends of the gas release device to reduce bubble coalescence, lowering the velocity gradient of the DAF water to avoid floc breakage, and providing collision surfaces along the flow path to optimize reaction conditions.
Compared with conventional flotation technology, CDFU also has general advantages: smaller bubbles with larger specific surface area and more thorough contact with suspended matter for better purification; lower required gas pressure, reduced energy consumption, and improved operating efficiency; and strong adaptability to suspended matter such as oil and floating/settling solids in wastewater.
CDFUCase: cyclonic dissolved air flotation technology for refinery wastewater treatment
As an efficient and rapid solid-liquid separation technology, flotation is widely applied, covering water supply and drainage treatment (especially for low-temperature, low-turbidity, algae-rich water), municipal domestic sewage treatment, and industrial wastewater treatment in many industries such as oil refining, chemicals, tanning, papermaking, textiles, printing and dyeing, steel, food, and pharmaceuticals. It is most commonly used in oily wastewater treatment, where effluent oil content can be controlled below 10~25 mg/L, meeting the biochemical treatment requirement for residual oil in the influent (generally below 25 mg/L).
