Why No Single Unit Fits Every Oily Stream: Route Selection with CDFU, CDOF, KFM and KHC

Industrial wastewater does not come in one flavour. Two plants a few hundred kilometres apart can hand you streams that share nothing but the word wastewater — one loaded with free oil, one so heavily emulsified that gravity settling does nothing, one dark and smelling of refractory organics. That variability is the reason a process route copied from a neighbour's project so often underperforms. Selection has to start from what is actually in the water and what the permit demands on the other side.

Read the water before choosing the hardware

Four questions settle most of the routing decision before anyone looks at a datasheet.

• Is the oil mostly free and dispersed, or locked into stable emulsions?
• Are COD, colour and odour the binding constraint rather than oil?
• Do suspended solids, colloids or iron travel along with the oil?
• Does the discharge point require a polished, near-oil-free effluent?

SINOKLE has assembled its treatment portfolio around exactly this kind of triage: a coalescing deoiler, CDFU swirl dissolved-air flotation, the integrated CDOF ozone advanced-oxidation flotation unit, the KFM activated-media filter and the KHC high-efficiency coalescing deoiler. Each module carries a different job, and the engineering value sits in the sequence rather than in any single vessel.

High-oil refinery streams: knock the bulk out first

Desalter draw-off water, crude tank-farm draw-off, refining black water and oil-depot sewage share a profile: plenty of free oil, a good deal of dispersed oil, some emulsified fraction, and an influent oil number that swings with upstream operations. Push that straight into biology, filtration or membranes and you buy shock loads, fouling and an effluent that never settles down.

The pairing that works is a coalescing deoiler ahead of CDFU. The deoiler takes the free and dispersed fraction off the top and drops the downstream load; CDFU then works on fine droplets, emulsified oil and suspended solids through swirl separation, micro-nano bubble flotation and coalescence. At a petrochemical complex in Xinjiang treating desalter and tank-farm black water, the line ran a high-efficiency coalescing deoiler plus two-stage CDFU at 150 m³/h. Influent oil came in at ≤20,000 ppm and left at ≤150 ppm, with oil-in-water held to ≤30%.

Extremely high-oil acidic water: two deep-deoiling steps

Coking acidic water and comparable high-oil acidic streams are a different problem. Concentration is high, oil forms are mixed, and part of the droplet population is fine enough and emulsified enough that single-stage flotation or a plain separator never reaches a stable number.

Here the recommended pairing inverts the emphasis: CDFU takes the first cut, handling rapid deoiling, solids removal and load reduction, and the KHC high-efficiency coalescing deoiler follows to force coalescence of what is left. A Sinopec coking acidic-water project in Henan ran CDFU plus KHC at 15 m³/h, taking influent oil from ≤150,000 ppm down to ≤100 ppm at the outlet. For water that concentrated and that stubborn, the combined route holds a stability that a single unit cannot.

Oil depots and intermittent discharge: protect the media

Light-oil depots, heavy-oil tank farms, accident drainage and other intermittently discharged oily water behave badly in a different way. Feed is discontinuous, oil content jumps around, and local shock loads can push the inlet close to an oil–water mixture. Equipment has to absorb that without losing separation depth.

Putting a filter ahead of the KHC coalescing deoiler answers it. The filter strips particulates and debris so they never reach the coalescing media, and the KHC then delivers the deep separation. On the light-oil depot at the Ansai back-pressure cogeneration construction project in Yan'an, filter plus KHC at 3 m³/h handled influent oil of ≤500,000 ppm and averaged ≤5 ppm in the treated water.

Composite oilfield water: three jobs, three units

Oilfield produced water, fracturing flowback fluid and drilling waste liquid rarely present oil alone. Suspended solids, colloids, iron ions and refractory organics come along, so deoiling by itself solves only a fraction of the permit problem.

The CDFU + CDOF + KFM route divides the work cleanly. CDFU handles front-end deoiling and solids removal so oil and particulates stop punishing downstream equipment. CDOF applies ozone multi-catalytic oxidation with swirl-enhanced mass transfer to attack refractory organics, colour and odour. KFM sits at the end as the polishing filter, trimming residual oil and fine solids. The front end brings oil and particulates down, the mid-stage deals with what will not biodegrade, and the back end stabilises the number.

Landfill leachate: the objective shifts to COD

Leachate from landfills and waste-incineration plants is hard for a different reason — high COD, deep colour, obvious odour, poor biodegradability. Deoiling is not the point; COD reduction, decolorization, deodorization and a steadier feed to whatever follows are.

The CDOF ozone advanced-oxidation flotation integrated unit is built for it, folding ozone advanced oxidation, catalytic oxidation, swirl-enhanced mass transfer and flotation separation into one shell to lift ozone utilisation and reaction efficiency. At a waste-incineration power plant in Shiyan, Hubei, MBR effluent COD of ≤1,300 mg/L came out of CDOF at ≤400 mg/L with chromaticity ≤30 and no perceptible odour; downstream biology then finished at COD ≤20 mg/L, ammonia nitrogen ≤1 mg/L and total phosphorus ≤0.2 mg/L.

Terminal assurance: where KFM earns its place

Once deoiling, flotation or oxidation has done its work, plenty of projects still need residual oil and fine suspended solids brought down another notch. The KFM activated-media filter is the terminal unit for that. Its media is modified to be super-hydrophilic, which gives high filtration precision, low differential pressure, strong anti-fouling behaviour, easy cleaning and long service life — properties that suit oilfield produced water and refinery or chemical effluent alike.

Fed at ≤50 ppm oil and ≤50 mg/L SS, the KFM outlet reaches ≤6 ppm oil, ≤2 mg/L SS and a median particle size of ≤1.5 μm. For reuse, reinjection, further advanced treatment or straight compliant discharge, that margin is what keeps a plant out of trouble.

What the pattern adds up to

Across all six cases the logic repeats: front-end load reduction, mid-stage intensification, back-end assurance. High-oil refinery water wants coalescing plus CDFU. Extremely high-oil acidic water wants CDFU plus KHC. High-shock depot water wants filtration plus coalescing. Composite oilfield water wants CDFU, CDOF and KFM together. Leachate wants CDOF for COD, colour and odour. Fine filtration at the tail wants KFM. That modular configuration is what lets SINOKLE push oil, suspended solids, COD, chromaticity and odour down at the same time instead of trading one against another.