Compared with DAF: How CDFU Swirl Dissolved-Air Flotation Is Reshaping Oily Wastewater Treatment
In industrial oily wastewater treatment, dissolved-air flotation (DAF) technology long held the dominant position. However, as environmental standards tighten, land becomes scarcer and operators demand better running economics, an innovative technology called CDFU (swirl dissolved-air flotation) is leading an industry-wide technology shift with its disruptive performance.
I. A Leap in Efficiency and Speed: From Marathon to Sprint
Conventional DAF relies on slowly mixing wastewater with dissolved-air water in open or semi-open tanks and using large bubbles (usually tens to hundreds of microns across) to carry pollutants to the surface. This needs a long hydraulic retention time, typically 15 to 40 minutes.
Figure: a conventional DAF installation on site
By contrast, CDFU technology uses a revolutionary dual-tangential inlet design to create instantly a highly stable, powerful swirl field inside the vessel. Wastewater and dissolved-air water rich in ultra-fine bubbles (only 5-30 microns across) collide and mix violently in this swirl field.
Figure: an oily wastewater treatment installation at an oilfield in north China (two-stage CDFU swirl vessel flotation + filter)
Under powerful centrifugal force, micro-bubbles attach to and coalesce with tiny oil droplets and suspended particles and rapidly concentrate towards the centre. This cuts hydraulic retention time to under 5 minutes, achieving 3 to 8 times the efficiency of conventional DAF - a fundamental leap from 'long wait' to 'instant separation'.
II. A Generational Gap in Treatment Precision: From Coarse Screening to Fine Filtration
Treatment precision is the core measure of how advanced a flotation technology is. Limited by larger bubble size and a non-uniform flow field, conventional DAF often cannot guarantee removal efficiency for pollutants below 10 microns, and is helpless against more stubborn emulsified oil (0.1-20 microns).
CDFU's ultra-fine bubbles are small and evenly distributed with an enormous specific surface area, greatly increasing the chance of collision and attachment with pollutants. Combined with its optimised swirl field, it efficiently removes fine suspended solids and emulsified oil droplets below 2 microns. This lets CDFU single-stage deoiling efficiency comfortably exceed 90%, far above the 60%-85% of conventional DAF, laying a solid foundation for downstream advanced treatment or direct compliant discharge.
III. A Fundamental Change in Footprint and Engineering Model
Conventional DAF systems usually need large reinforced-concrete tanks, occupy a lot of land and are mostly cast in situ, with long construction periods - very unfriendly to plant retrofits. CDFU technology, by contrast, integrates all functions into one or more pressure vessels in a fully skid-mounted, modular design.
Its compact structure means it occupies only one third of the footprint of a conventional DAF system with the same capacity. This 'factory prefabrication, on-site assembly' model simplifies complex civil engineering into fast equipment hook-up, greatly shortening project schedules and making it especially suitable for offshore platforms and space-constrained plant retrofits.
IV. A Green Upgrade in Operating Philosophy: From Chemical Dependence to Physical Purity
To improve demulsification and flocculation, conventional DAF usually requires continuous dosing of demulsifiers, coagulants and other chemicals. This not only adds ongoing chemical procurement cost but, more importantly, the chemicals combine with pollutants to produce large amounts of oily chemical sludge. Such sludge is hazardous waste with expensive disposal and a risk of secondary pollution.
CDFU technology upholds a 'purely physical separation' philosophy: its efficient swirl centrifugation and micro-bubble attachment mechanisms achieve excellent demulsification and separation without any chemicals. This completely eliminates chemical sludge, cutting hazardous-waste disposal costs and environmental risk, while the separated floating oil is purer and easier to recover - a genuine unity of environmental and economic benefit.
Figure: an oily wastewater treatment installation at a heavy-oil power plant (two-stage CDFU swirl vessel flotation + KFM filter)
V. Full Leadership in Automation and Stability
Conventional DAF systems are often poorly automated and rely on manual operation and judgement, such as manually controlled sludge scrapers, so operating stability is easily affected by human factors and water quality fluctuations.
CDFUAs a fully enclosed pressure system, it was designed for intelligent control from the outset. It integrates advanced sensors and a PLC control system to control key parameters such as level, pressure and flow precisely and automatically (level control accuracy can reach within 5 mm), and can adjust operating status automatically to influent conditions. This high degree of automation means the system tolerates flow fluctuations of 10%-120% and delivers long-term, stable, highly efficient unattended or minimally attended operation - a perfect fit for modern smart wastewater treatment plants.
In summary, CDFU is not a simple improvement on conventional DAF technology but a comprehensive renewal spanning principle, structure and operating philosophy. It achieves leapfrog improvements in treatment efficiency, precision, footprint, environmental performance and operating stability. For power plants facing severe environmental pressure and urgently seeking cost reduction, efficiency gains and intelligent upgrading, CDFU technology undoubtedly represents a more advanced, more economical and more sustainable direction for oily wastewater treatment.
