In-Depth Breakdown of CDFU Cyclonic Dissolved Air Flotation: How Do Cyclone, Micro-Bubbles, Dissolved Air and Coalescence Work Together?
Everyone working in industrial wastewater treatment knows that a single technology can never handle complex water quality. Equipment that truly holds up on site is always the result of several technologies working together. Today we will take apart, one by one, the four core technologies of SINOKLE'sCDFUcyclonic dissolved air flotation unit, explaining what each of them does and how they work together.
Technology 1: Cyclonic Centrifugal Separation— The Workhorse of Coarse Separation
Oily wastewater enters theCDFUvessel at high speed through a tangential inlet, forming a powerful cyclonic field inside the cylindrical chamber. Using the density difference between oil and water (oil about 0.8–0.95 g/cm³, water about 1.0 g/cm³), centrifugal force drives the less dense oil droplets toward the centre of the cyclone to form an oil core, while the heavier clean water moves outward along the vessel wall. This process separates most free oil droplets within a few seconds to a few tens of seconds, serving as the first highly efficient “coarse filtration” stage of the entire unit. Another key role of cyclonic separation is that it creates a turbulent, thoroughly mixed environment for the subsequent bubble contact — not stagnant water, but dynamic contact within high-speed rotation, where the collision probability is far higher than in a static DAF.
Technology 2: Ultra-Fine Bubble Generation— The Trump Card Against Emulsified Oil
This is whereCDFUdiffers most from conventional flotation. The bubbles released by dissolved air in a conventional DAF are mostly 50–100 μm in diameter, whereasCDFUuses SINOKLE's in-house new-generation micro-bubble generation technology to control bubble size down to the nanometre-to-micrometre scale. Why are smaller bubbles better? Because the smaller the bubble diameter, the larger the total surface area for the same gas volume (specific surface area is inversely proportional to diameter), and therefore the larger the contact area with emulsified oil droplets in the water. At the same time, micro-bubbles rise more slowly and stay in the water longer, greatly increasing the probability of oil droplet–bubble collision and adhesion. Here is an analogy: catch fish with a large net and the small ones slip through; switch to fine sand filtration and nothing escapes — ultra-fine bubbles are that “fine sand net.”
Technology 3: Dissolved Air Flotation— The Classic Separation Driver
Dissolved air flotation is the basic framework of the whole system. Inside theCDFUunit, part of the treated effluent is pressurized to 0.3–0.6 MPa and injected with compressed air or nitrogen to form supersaturated dissolved-air water, which is then released at reduced pressure inside the vessel through a dedicated release device. The essence of this process lies in controlling the two steps of “dissolving” and “releasing” — dissolution efficiency determines the total number of bubbles available, while the structure of the release device determines how uniform the bubble size distribution is. SINOKLE has made patented optimizations at both steps, so that theCDFUachieves significantly higher dissolved-gas utilization than a conventional DAF, with lower energy consumption at the same treatment capacity.
Technology 4: Coalescence and Demulsification— Making the “Stubborn Ones” Stick Together
A considerable proportion of the oil in industrial wastewater exists in emulsified form— the surface of the oil droplets is wrapped in surface-active substances, forming a stable oil-in-water (O/W) emulsion in which droplets repel one another because of electrical charge and are hard to aggregate. Coalescence and demulsification technology uses special internals or media so that emulsified oil droplets collide and merge as they flow past, turning small droplets into large ones that are more easily captured by cyclonic centrifugal force or adhered to by bubbles. This step may look like a supporting act, but it is in fact the critical leap that pushes oil removal efficiency from “90%+” to “99%+” — without demulsification, even the finest bubbles are helpless against charge-protected emulsified oil droplets.
The Logic of Four-in-One Synergy
These four technologies are not simply connected in series; they are spatially nested and functionally complementary. The cyclone provides a centrifugal force field and mixing energy, coalescence enlarges emulsified oil droplets, ultra-fine bubbles provide an enormous “capture surface,” and dissolved air flotation supplies both the bubbles and the flotation driving force— all four steps take place simultaneously in the same sealed vessel, reinforcing one another.
Engineering data also confirm the effectiveness of this synergistic logic: at a petrochemical plant in Shandong, inlet oil content was250,000 mg/L with effluent below 150 mg/L (99.9%); in an ultra-heavy oil project, inlet oil content was 150,000 mg/L with effluent below 40 mg/L (99.97%); and at heavy-oil power plants in Sierra Leone and Bangladesh, effluent oil content was below 5 and 10 mg/L respectively. Treatment capacities span the full range from 5 to 250 m³/h, showing that this synergistic architecture maintains good stability as it scales up.
Technical summary:CDFUat its core works within a compact sealed space: cyclonic centrifugation handles the “big lumps,” coalescence and demulsification break down the “stubborn ones,” ultra-fine bubbles round up the “ones that slip through the net,” and dissolved air flotation completes the final transport — four approaches at once, purely physical, with no chemicals at any stage. Judging from actual operating data in the field, the competitiveness of this technology route in industrial oily wastewater treatment hardly needs further comment.
