CDFU vs Conventional CFU Flotation: Bubbles, Mass Transfer and Operating Cost

Industrial wastewater has grown more complex. Poorly degradable organics take a larger share of the load, and high salinity and high organic load are now routine problems rather than edge cases. Against that feed, conventional CFU (conventional flotation) technology shows its limits: low mass transfer efficiency, incomplete pollutant removal, poor adaptability to water quality and high energy consumption. Independently developed by SINOKLE, CDFU (compact dissolved-air swirl flotation) technology keeps the core logic of flotation and rebuilds it around ultrafine nanobubble generation and swirl-enhanced dissolved air.

Bubbles: millimetres versus microns

Conventional CFU flotation produces bubbles mostly in the millimetre range - sparse in number and with a small specific surface area, which caps the gas-liquid contact area available per unit volume. CDFU reaches micron and nanometre bubble diameters; combined with swirl shear, the bubbles are more uniformly distributed and denser, and the specific surface area is far larger. Gas-liquid contact efficiency is 5-10 times higher.

Mass transfer: seconds versus hours

Conventional bubbles rise quickly, around 20-30 cm/s, and their retention time is measured in seconds, which leaves insufficient time for gas-liquid mass transfer; dissolved oxygen and oxidant utilisation usually sits below 60%. CDFU bubbles rise slowly, below 5 cm/s, and the swirl effect extends water retention time to several hours. Because the bubbles self-shrink and keep releasing dissolved gas, mass transfer efficiency improves by more than three times and oxidant utilisation exceeds 95%.

Bubble stability differs in the same way. Conventional bubbles coalesce and burst readily and persist for minutes, so the reaction lacks continuity. Under the combined action of surface charge and the swirl field, CDFU bubbles resist coalescence and stay stable for hours, which keeps the reaction running to completion. That matters because bubble collapse creates local high-temperature, high-pressure conditions that crack water molecules and generate hydroxyl radicals and other strongly oxidising species in situ - something conventional flotation, which relies on bubble adsorption alone, cannot produce at all.

Removal depth

Conventional CFU removes some suspended pollutants by physical bubble adsorption, but for poorly degradable organics in the pharmaceutical, petrochemical and printing and dyeing sectors - benzene series compounds, antibiotics, chlorinated organics - removal is only 40%-50%, and intermediates can accumulate and raise toxicity. CDFU combines physical adsorption with chemical oxidation: the high specific surface area of ultrafine nanobubbles strengthens capture, and the in-situ active species attack pollutant molecular structures directly while swirl mixing improves reaction uniformity. On petrochemical ethylene wastewater with COD of 1,500-2,000 mg/L, CDFU raises COD removal from 42% under conventional CFU to 83% and benzene series removal from 51% to 95%.

Water quality range

Conventional flotation is sensitive to water quality swings, particularly in high-salinity conditions such as reverse osmosis concentrate with TDS above 10,000 mg/L, where salt ions suppress dissolved-air efficiency and adsorption and performance decays quickly. CDFU tolerates it: for high-salinity wastewater with TDS up to 58,000 mg/L or more, the active substances it generates decompose chlorinated organics without being inhibited by salt ions, and days of continuous operation leave activity decay at only one third that of CFU. Under high organic load, swirl-enhanced dissolved air replenishes oxygen or oxidant quickly enough to avoid a treatment bottleneck.

Operating economics and durability

Conventional flotation wastes both energy and chemicals: aeration equipment runs heavily loaded, and low dissolved-air efficiency means oxidants such as ozone are consumed inefficiently at utilisation below 60%. CDFU saves on both counts. Ultrafine nanobubbles cut ozone consumption by more than 40%, and the swirl dissolved-air design reduces the aeration load, cutting power consumption by 30%-50%. The compact structure lowers equipment investment and footprint as well, bringing overall operating cost more than 35% below CFU.

Durability follows the same pattern. Conventional CFU often depends on catalysts or auxiliary microbial systems, so it is easily disturbed by water quality and temperature swings, and the reactor tends to scale and foul, with an average service life of only 2-3 years and a risk of secondary pollution from metal leaching. CDFU needs no complex catalyst or microbial system, relies on physical and chemical action, and is barely affected by water quality fluctuation. It meets the heavy metal discharge standard GB 8978-1996 with no secondary pollution risk, and swirl shear reduces attachment and scaling, so service life extends beyond 5 years.

For plants working with poorly degradable, high-salinity or high-load wastewater, the upgrade does not require rebuilding the process. Replacing the flotation stage with CDFU delivers the depth, adaptability and running cost the conventional unit could not.

The pattern holds across sectors. Pharmaceutical, petrochemical, printing and dyeing and coal chemical plants all feed the same combination of hard organics, salt and load into their flotation stage, and all of them benefit from a bubble population that survives long enough to react instead of rising out of the vessel in seconds. That is the practical difference between extending a conventional unit and replacing it.