CDOF Ozone Catalytic Oxidation Flotation Integrated Unit: Dissecting a Five-Stage Advanced Treatment Process Chain from an African Large-Scale Oilfield's 250 m3/h Produced-Water Project
The second-phase integrated oilfield wastewater treatment project of a large-scale oilfield in Africa has a treatment capacity of 250 m3/h and an effluent oil content of <5 mg/L. Behind this figure lies an engineering-proven five-stage advanced treatment process chain. This article dissects the technical principles and process roles of each piece of equipment stage by stage.
Stage 1:CDFUCyclonic Dissolved Air Flotation - the main oil-removal stage
The incoming water is a mixture of joint-station wastewater (4,000 m3/d) + fracturing flowback fluid (1,750 m3/d) + drilling waste fluid (250 m3/d), with high oil content and severe emulsification.
CDFU(Cyclonic Dissolved Gas Flotation Unit) here undertakes the task of the 'first line of defense.' Its technical architecture stacks four core modules: the cyclonic centrifugal separation module uses tangential inflow to generate a high-speed rotating flow field, achieving the preliminary separation of oil-water-solid three phases under centrifugal force; the ultra-fine bubble generation module produces micro-bubble groups with a diameter of 30-50 mum through dissolved-air release, whose specific surface area is far larger than the 80-100 mum bubbles of conventional DAF, significantly improving the capture efficiency of fine oil droplets; the coalescence-demulsification module is designed for emulsified oil, using special coalescing material to make tiny emulsified oil droplets collide and merge into larger ones, reducing the difficulty of subsequent flotation separation; the dissolved air flotation module uniformly separates the products of the above modules. The four modules operate synergistically in a sealed, pressurized tank, with no VOC escape.
Stage 2: Coagulation-Sedimentation Tank - the colloidal coagulation stage
CDFUThe suspended solids in the effluent are mainly in colloidal form (particle size 1-100 nm); electrostatic repulsion keeps them stably dispersed and physical separation is ineffective. Coagulation-sedimentation uses the charge neutralization and adsorption-bridging action of added inorganic coagulants (aluminum or iron salts) to destabilize and flocculate the colloids, then settles them by gravity. The SS of the effluent from this stage can usually be reduced to 30-50 mg/L.
Stage 3:CDOFOzone Catalytic Oxidation Flotation Integrated Unit - the advanced oxidation core
This is the most technology-intensive equipment in the whole process chain and is also SINOKLE's PCT international patented product.
CDOF(Cyclonic Dissolved Ozone Flotation) essentially accomplishes two unit operations-'advanced oxidation' and 'flotation separation'-simultaneously within a sealed pressurized vessel.
Oxidation side: an oxygen-generation system produces oxygen with a purity >=90%, which is converted into ozone by an ozone generator and injected into the reactor through an efficient dosing system. In the multiple catalytic reaction zones, three catalytic paths run simultaneously-(1) homogeneous catalysis: dissolved metal ions catalyze ozone decomposition to produce .OH; (2) heterogeneous catalysis: the active sites on the solid catalyst surface adsorb ozone and organic matter, lowering the reaction activation energy; (3) supercritical catalytic oxidation: local zones in the reactor approach the supercritical state of water (374 degrees C / 22.1 MPa) under specific temperature and pressure, where the organic matter and oxidant form a homogeneous phase, mass-transfer resistance approaches zero, and the oxidation rate increases by orders of magnitude.
The hydrodynamic cavitation module creates periodic pressure fluctuations in the reaction zone; bubbles form, grow and violently collapse, and at the instant of collapse the local hot-spot temperature can reach 5,000 K and pressure about 1,000 atm, producing .OH and H2O2 while also tearing apart macromolecular organics and increasing the contact area for subsequent oxidation.
Flotation side: after the oxidation reaction, the mixed liquid enters the cyclonic dissolved air flotation zone, where micro-bubbles released from dissolved air separate the flocs produced by oxidation and the residual suspended solids. The oxidation + flotation integration avoids the problems of ozone escape and floc breakage caused by pipeline transfer between the ozone contact tower and the flotation tank in the traditional process.
CDOFThe COD removal rate is usually 60%-85% (depending on influent quality), and it also has a significant removal effect on petroleum, colloids and bacteria.
Stage 4: TerminalCDFUCyclonic Dissolved Air Flotation - the secondary fine-removal stage
CDOFThe effluent may still contain a small amount of oxidized and modified suspended solids and trace floating oil; the terminalCDFUstage performs a secondary fine separation. The working conditions here are far superior to those of the first stageCDFU-the influent oil content has been greatly reduced, and the main task is the final flotation separation of oil droplets and suspended solids smaller than 20 mum.
Stage 5: KFM Modified Filter Media Filter - the end-of-line safeguard stage
The core technology of KFM (SINOKLE Modified Filter Media) lies in surface modification of the filter media-functionalizing the surface of quartz sand or ceramic pellet substrate (introducing specific functional groups or surface coatings) so that the media surface develops a selective adsorption affinity for petroleum substances. Compared with traditional quartz sand filtration, which relies only on physical interception, KFM combines physical interception + surface adsorption in a dual mechanism, improving the removal efficiency of emulsified and dissolved oil by 30%-50% over ordinary filters. The effluent oil content is stably <5 mg/L.
Overall Assessment of the Process Chain
From CDFU (Physical separation) -> Coagulation-Sedimentation (chemical coagulation) ->CDOF(Advanced oxidation + flotation) -> TerminalCDFU(Secondary physical separation) -> KFM (deep filtration). The design logic of this five-stage chain is the typical strategy of 'progressively reducing load and setting graded targets.' Each stage has clear technical boundaries for its influent conditions and effluent requirements-no waste and no weak links. The continuous and stable operation of the large African oilfield project at 250 m3/h proves that this process chain has moved from theoretical optimality to engineering reliability.
