Flotation is a solid-liquid or liquid-liquid separation technology in which highly dispersed micro-bubbles are introduced into the water body. The bubbles attach to the surface of suspended particles or are enveloped by them, forming a gas-liquid-solid three-phase mixture. Utilizing the apparent density difference between this three-phase system and water, solid and liquid particles float to the water surface, thereby achieving solid-liquid or liquid-liquid separation.

Dissolved Air Flotation (DAF) refers to pre-dissolving air into water under high pressure until saturation; when the pressure drops abruptly, the dissolved gas is released as micro-bubbles, typically 10-100 um in diameter. A complete DAF process comprises four basic stages: pretreatment, dissolved-air release, bubble-floc aggregate formation, and bubble-floc aggregate separation. These four stages occur respectively in the coagulation-flocculation system, the dissolved-air release system, and the contact and separation zones of the flotation tank.

Based on the centrifugal separation principle, we designed the cyclonic dissolved-air flotation device (CDFU) that couples the centrifugal force field with the flotation separation process. Pressurized water flows through an ejector to create negative pressure that draws in gas; the gas and high-speed water stream mix and shear to form micro-bubbles. The centrifugal force field drives floc particles/oil droplets and bubbles to move radially toward the field center. Compared with traditional flotation, the bubbles and floc particles/oil droplets possess inertia, freeing them from streamline constraints and forming a more ordered collision and attachment process, thereby intensifying the separation of floc particles/oil droplets from the water body.

Compared with traditional flotation, the cyclonic dissolved-air flotation device (CDFU) offers the following advantages:

1. Adopts high-efficiency ejectors combined with ultra-micro-nano bubble technology; the generated bubbles mix thoroughly with wastewater without excessively breaking flocs; few power devices, simple structure, and fully enclosed operation.

2. The cyclonic pressurized dissolved-air tank generates large amounts of stable micro-bubbles; increasing bubble-oil droplet contact time, enlarging oil-droplet diameter, reducing bubble diameter, and raising micro-bubble concentration effectively improves the collision probability and attachment efficiency between bubbles and oil droplets, thereby enhancing oil-removal efficiency.

Its features include:

1) Eliminates dead ends in the releaser to reduce bubble coalescence;

2) Allows the dissolvedair-water velocityto gradually decrease inside the releaser, preventing breakage of flocs in the raw water;

3) Provides collision surfaces along the flow path.

In summary, compared with traditional flotation technology, the cyclonic dissolved-air flotation device (CDFU) has the following distinct advantages:

1. DAF uses smaller bubbles with larger surface area, enabling more effective contact with suspended matter and improving purification.

2. DAF can generate bubbles at lower gas pressure, reducing energy consumption and improving operational efficiency.

3. DAF adapts well to suspended matter such as oil and floating solids in wastewater.

As a highly efficient and rapid solid-liquid separation technology, flotation is now widely applied in water supply and drainage, especially for purification of low-temperature, low-turbidity, and algae-rich water bodies, as well as municipal domestic sewage and industrial wastewater from oil refining, chemicals, leather, paper, textiles, dyeing, steel, rubber, food, light industry, and pharmaceuticals. It is most common in oily wastewater treatment, where effluent oil content can be below 10-25 mg/L, and generally below 25 mg/L after biological treatment.

Cyclonic pressurized dissolved-air flotation technology for oily wastewater treatment:

Cyclonic dissolved-air flotation deviceCDFUtreating desalter wastewater

process flow diagram

desalter wastewater treatment process flow diagram

Process Advantages

1. Pure physical separation technology, stable, reliable, and highly efficient (over 95% oil removal)

2. Chemical-free pure-physical demulsification and oil removal; recovered oil is of good quality and can be re-refined, generating no oily sludge (hazardous waste), solving environmental problems while creating economic benefits;

3. Short process flow, compact equipment structure, small footprint,

4. Skid-mounted, automated, easy to operate and maintain, short construction period, implementable online

5. Strong shock resistance, stable operation, able to withstand large water-quality fluctuations;

Process Effect