CDFU versus Conventional DAF: A Comparative Analysis of Flotation Technologies
CDFU (cyclonic dissolved gas flotation) and DAF (dissolved air flotation) are two physical separation technologies commonly used in oily wastewater treatment, differing significantly in principle, efficiency and applicability.
1. Basic Introduction
CDFU (Compact Cyclonic Dissolved Gas Flotation)
CDFU is an innovative high-efficiency oil-water separation system combining cyclonic centrifugal separation with dissolved air flotation (DAF). Its core features include:
Bubble characteristics: ultra-fine bubbles generated by a multi-stage, specially structured cyclonic dissolved gas pump, typically 5-30 um in diameter (median diameter D50 of about 25 um), with high bubble uniformity.
Separation mechanism: after mixing with dissolved gas water, the wastewater enters the cyclonic flotation tank tangentially; under the synergy of centrifugal force and micro-bubbles, the collision probability and adhesion efficiency between oil droplets and bubbles are greatly increased, achieving rapid flotation and oil-water separation.
(The figure above shows an oily wastewater treatment project at a thermal power plant, using two-stage CDFU plus filters, with a capacity of 5 m3/h and a total skid footprint of about 16 m2)
Technical advantages:
Efficient removal of emulsified oil (0.1-20 um droplets), with single-stage oil removal above 90%.
Purely physical separation with no chemical dosing, avoiding the generation of oily sludge (hazardous waste); the separated oil can be recovered and reused.
Short hydraulic retention time (under 5 minutes); compact equipment with a footprint only 1/3 of conventional DAF.
Fully automatic closed operation, strong shock-load resistance and high effluent stability.
Application: particularly suited to difficult, highly emulsified oily wastewater, such as oilfields, offshore platforms and land-constrained projects.
DAF (Dissolved Air Flotation)
DAF is the conventional dissolved air flotation technology; its basic principles are:
Bubble characteristics: bubbles generated by a dissolved gas pump or pressurised dissolution, with a wide diameter range (5-100 um) and moderate uniformity.
Separation mechanism: large numbers of micro-bubbles are introduced into the wastewater; acting as carriers, they adsorb suspended particles (such as oil droplets) or flocs to form aggregates with a density lower than water, which rise to the surface by buoyancy and are removed as scum.
Technical features:
For conventional oily wastewater, single-stage oil removal efficiency is about 60%-85%.
Coagulants or flotation agents are usually required, raising operating costs and generating oily sludge with a risk of secondary pollution.
Long hydraulic retention time (15-40 minutes), large footprint, and treatment performance easily affected by water-quality fluctuations.
Mostly open-type, manually operated designs.
Application: more suited to onshore plants and stations where footprint is not critical, for conventional oily wastewater.
2. Comparison of Core Technical Parameters
3. Treatment Performance and Operating Stability
Conventional DAF relies on dissolved gas pumps to generate bubbles, with a wide and non-uniform size distribution, limited capability to remove emulsified oil (0.1-20 um) and fine suspended solids, and performance easily affected by water-quality fluctuations.
CDFU Through the synergy of cyclonic centrifugal force and ultra-fine bubbles (5-30 um), the collision probability and adhesion efficiency between oil droplets and bubbles are greatly increased. Its unique multi-stage cyclonic design enhances fluid turbulence, enabling micro-bubbles to adsorb emulsified oil droplets more effectively for efficient separation. Therefore, CDFU can achieve high-precision effluent consistently without chemical dosing, and is especially adept at treating refractory emulsified oily wastewater.
4. Economics and Environmental Performance
Footprint: CDFU compact structure, with a footprint only 1/3 of conventional DAF.
Energy and chemical consumption: conventional DAF requires coagulants or flotation agents, with high operating costs and large amounts of oily sludge (hazardous waste), creating a risk of secondary pollution.CDFU uses purely physical separation with no chemicals, avoiding hazardous sludge at the source and reducing subsequent disposal costs.
Automation and O& M: CDFU fully automatic closed operation with no manual scum scraping, simple O& M, and long-term operating costs significantly lower than conventional DAF.
5. Application Scenarios
Conventional DAF: more suited to onshore plants and stations where footprint and weight are not critical, for conventional oily wastewater.
CDFU: its skid-mounted, compact design makes it particularly suitable for offshore platforms, oilfields and land-constrained plants treating difficult, highly emulsified oily wastewater.
Overall, CDFU technology shows significant advantages in treatment efficiency, operating stability, environmental benefits and footprint, representing the development direction of oily wastewater pretreatment. For new-build or retrofit projects pursuing efficient, green and low-cost operation, CDFU is a more competitive solution than conventional DAF.
