Building an oily wastewater train: how CDFU flotation and CDOF oxidation fit together
Industrial oily wastewater rarely fails a single test. It fails a sequence of them: oil first, then suspended solids, then the dissolved fraction that no amount of settling will touch. Designing a treatment train is therefore an exercise in ordering, and the ordering chosen by SINOKLE for its core process line reflects that logic rather than a preference for one product.
Shenzhen SINOKLE Technology Co., Ltd., referred to throughout as SINOKLE, is a national high-tech enterprise dedicated to energy conservation and environmental protection. Since its founding in 2014 it has concentrated on the R&D and application of technologies for difficult oily wastewater treatment, building on independently developed core technologies such as CDFU cyclonic dissolved air flotation and CDOF catalytic ozonation.
Stage one: CDFU removes the load that poisons everything downstream
The starting point of the process flow is the water to be treated, which gathers biochemical water and backwash water. Facing complex industrial wastewater, SINOKLE adopts its core patented technology, the CDFU cyclonic dissolved air flotation unit. It is not a simple improvement of traditional flotation but an integration of two separation mechanisms that normally live in different vessels.
Wastewater generates a high-speed swirling flow through a special tangential inlet. At the same time the dissolved air system releases a large number of micro-bubbles with diameters of only 5-30 mum. Under the synergy of the centrifugal field and micro-bubbles, oil droplets and suspended solids dispersed in water are captured and float quickly to the liquid surface, achieving rapid solid-liquid and oil-water separation.
The performance gap against conventional equipment is wide. Traditional flotation units reach a removal rate of only 40%-60%; CDFU achieves an oil removal rate above 90% and a suspended solids removal rate above 85%. The whole treatment process requires no chemical dosing, being a purely physical separation technology that avoids secondary pollution. That combination of efficiency and cleanliness explains its use in oily wastewater projects of large enterprises such as CNPC, Sinopec and CNOOC.
Stage two: CDOF handles the dissolved remainder
After CDFU treatment most oil and suspended solids are gone, yet wastewater containing refractory organic matter still needs deep treatment to meet discharge or reuse standards. The process flow then enters the CDOF / CDFO ozone catalytic oxidation stage.
Independently developed by SINOKLE, the CDOF unit uses high-concentration ozone generated by an ozone generator and, under the synergy of a special catalyst, produces hydroxyl radicals with extremely strong oxidation capability. These radicals attack and mineralise residual organic pollutants non-selectively, effectively reducing chemical oxygen demand (COD) while delivering decolourisation, deodorisation and disinfection in the same pass. For saline and polymer-containing wastewater from refining and petrochemical plants, the unit improves effluent quality enough to create favourable conditions for compliant discharge or reuse.
The pairing matters more than either unit alone. Flotation is cheap per cubic metre but blind to dissolved organics; oxidation is powerful but wasteful if it has to burn oxidant on free oil that settling could have removed. Running them in this order keeps oxidant demand where it belongs.
Stage three: tail gas is not an afterthought
Ozone oxidation leaves residual ozone in the off-gas, and direct emission would affect the atmospheric environment. SINOKLE integrates an efficient tail gas treatment device, usually based on activated carbon adsorption or metal catalyst decomposition, which thoroughly decomposes the residual ozone into oxygen so that the emitted gas fully complies with environmental standards. It is a small part of the capital cost and a large part of what makes a full-process closed-loop claim credible.
Engineering culture behind the hardware
Technical strength shows up in single devices but also in the ability to provide overall solutions. SINOKLE maintains a high-quality R&D team led by doctors and masters and uses advanced CFD simulation tools for process optimisation. The track record runs from being rated a national high-tech enterprise in 2017 to the successful export of mobile treatment equipment to Poland in 2025 and entry into the high-end EU market; products and services have spread across major domestic industrial bases and been exported to many countries along the Belt and Road.
For a plant manager evaluating this kind of line, the useful question is not which unit is more advanced but where the boundary sits. CDFU owns the free and dispersed oil load and the solids; CDOF owns the dissolved and refractory fraction. Where wastewater is dominated by free oil, the first stage alone may be sufficient. Where dissolved COD must fall for a reuse standard, the second stage becomes mandatory rather than optional.
A combined process centred on physical separation and advanced oxidation achieves cascade utilisation and deep purification of industrial wastewater. That is the practical argument for the arrangement: each stage is asked to do only what it does efficiently.
Two operating details are worth flagging for anyone specifying such a line. The flotation stage needs a stable dissolved-air supply and a clean release device, because a fouled release point produces coarse bubbles and the oil removal rate falls quietly rather than dramatically. The oxidation stage needs its catalyst replaced on the supplier schedule and its ozone generator fed dry gas; moisture in the feed gas attacks both the generator and the catalyst. Neither requirement is exotic, but both are commonly deferred, and either can make a well-designed train look like a bad technology.