How to Select a Treatment Process for Complex Industrial Wastewater? SINOKLE's Combined-Technology Solutions

No single process can adapt to all water qualities in industrial wastewater treatment. Differences in influent sources, pollutant forms, treatment objectives and site conditions from one project to another dictate that the process route must also vary with the water. For high-oil wastewater, the core is rapid oil reduction; for highly emulsified wastewater, the key is demulsification and separation; for wastewater with high COD, high chromaticity and odor, the focus is advanced oxidation and advanced purification; and for projects with stringent effluent requirements, a terminal filtration or coalescing unit is needed for stable assurance.

Focusing on difficult industrial wastewater treatment, SINOKLE has formed a combined technology system composed of the coalescing deoiler, CDFU swirl dissolved-air flotation, the integrated CDOF ozone advanced-oxidation flotation unit, KFM activated-media filter and KHC high-efficiency coalescing deoiler. Different technical modules have different emphases, and through reasonable combination they can achieve multiple treatment objectives such as deoiling, demulsification, suspended-solids removal, COD reduction, decolorization, deodorization and effluent assurance.

I. High-oil refinery wastewater: give priority to 'coalescing deoiler + CDFU'

Applicable scenarios include desalter draw-off water, crude-oil tank-farm draw-off water, refining black water and oil-depot sewage. This type of wastewater usually contains a large amount of free oil, dispersed oil and some emulsified oil, with high influent oil content and obvious water-quality fluctuation. If it directly enters downstream biological, filtration or membrane treatment systems, it easily causes system shock, blockage and effluent fluctuation.

For this type of water quality, the combined process of 'coalescing deoiler + CDFU' is recommended. The coalescing deoiler first pre-separates free oil and dispersed oil to reduce the downstream load; the CDFU then further removes fine oil droplets, emulsified oil and suspended solids through swirl separation, micro-nano bubble flotation and coalescence.

In a desalter and tank-farm black-water treatment project of a petrochemical plant in Xinjiang, the combined process of 'high-efficiency coalescing deoiler + two-stage CDFU' was adopted, with a treatment capacity of 150 m³/h, influent oil content ≤20,000 ppm, and treated effluent oil content ≤150 ppm with oil-in-water rate ≤30%. This result shows that, for high-oil refinery wastewater, the front-end coalescing load reduction and multi-stage CDFU intensified separation can achieve a substantial reduction in oil concentration.

II. Extremely high-oil acidic water: give priority to 'CDFU + KHC high-efficiency coalescing deoiler'

Wastewater such as coking acidic water and high-oil acidic water is usually more difficult to treat. Such wastewater not only has high oil concentration but also complex oil forms, with some oil droplets being very fine and strongly emulsified. Traditional oil separation or single-stage flotation often struggles to achieve stable deep deoiling.

For this type of wastewater, the combined process of 'CDFU + KHC high-efficiency coalescing deoiler' is recommended. The CDFU first undertakes rapid deoiling, suspended-solids removal and system-load reduction; the KHC high-efficiency coalescing deoiler then further intensifies the coalescence of fine oil droplets to achieve deep oil–water separation.

In a coking acidic-water project of a Sinopec petrochemical plant in Henan, the 'CDFU + KHC high-efficiency coalescing deoiler' treatment route was adopted, with a treatment capacity of 15 m³/h, influent oil content ≤150,000 ppm, and treated effluent oil content ≤100 ppm. This case shows that, for extremely high-oil, strongly emulsified and hard-to-separate acidic water, the combined deep-deoiling route is more stable than a single treatment unit.

III. High-shock oil-depot wastewater: give priority to 'filter + KHC coalescing deoiler'

Light-oil depots, heavy-oil tank farms, accident drainage or intermittently discharged oily wastewater often feature large oil-content fluctuation, discontinuous feed and high local shock loads. Under some operating conditions the influent oil content is extremely high, even close to an oil–water mixture state, placing high demands on equipment shock resistance and separation depth.

For this type of wastewater, the combined process of 'filter + KHC coalescing deoiler' is recommended. The filter first removes particulates and impurities from the water to reduce their pollution of the coalescing media; the KHC coalescing deoiler then performs deep oil–water separation to ensure low-oil effluent.

In the oily-wastewater treatment of a light-oil depot in the Ansai back-pressure cogeneration construction project in Yan'an, the 'filter + KHC coalescing deoiler' was adopted, with a treatment capacity of 3 m³/h, influent oil content ≤500,000 ppm, and average treated effluent oil content ≤5 ppm. This case demonstrates the deep-separation capability of this combined process for high-shock, high-oil wastewater.

IV. Composite oilfield and fracturing flowback fluid: give priority to 'CDFU + CDOF + KFM'

Wastewater such as oilfield produced water, fracturing flowback fluid and drilling waste liquid has a more complex pollutant composition, usually not only containing oil but also possibly suspended solids, colloids, iron ions and refractory organics. For this type of water quality, deoiling alone cannot solve all problems; deoiling, COD reduction, suspended-solids removal and terminal water-quality assurance must be considered simultaneously.

For composite oilfield wastewater, the 'CDFU + CDOF + KFM' combined route is recommended. The CDFU is used for front-end deoiling and suspended-solids removal, reducing the impact of oil and particulates in the water on downstream units; the CDOF uses ozone multi-catalytic oxidation and swirl-enhanced mass transfer to deeply treat refractory organics, chromaticity and odor; and the KFM activated-media filter serves as the terminal assurance unit, further reducing residual oil and fine suspended solids.

The advantage of this combined process lies in its clear division of labor: the front end first brings down oil and particulates, the mid-stage then treats refractory organic pollutants, and the back end stabilizes the effluent through filtration. For comprehensive oilfield wastewater with complex water sources and high treatment objectives, this route has strong adaptability.

V. Landfill leachate advanced treatment: give priority to the 'CDOF ozone advanced-oxidation flotation integrated unit'

Wastewater such as landfill leachate, waste-incineration-plant leachate and landfill-site leachate is mainly difficult because of high COD, deep chromaticity, obvious odor and poor biodegradability. The core treatment objective for such wastewater is no longer deoiling, but COD reduction, decolorization, deodorization and improved stability of subsequent treatment.

For this type of wastewater, the CDOF ozone advanced-oxidation flotation integrated unit is recommended. The CDOF integrates ozone advanced oxidation, catalytic oxidation, swirl-enhanced mass transfer and flotation separation into one, improving ozone utilization and oxidation-reaction efficiency and achieving refractory-organic reduction, chromaticity reduction and odor removal.

In a landfill-leachate treatment project of a waste-incineration power plant in Shiyan, Hubei, the MBR effluent COD was ≤1,300 mg/L; after CDOF treatment the COD was ≤400 mg/L, chromaticity ≤30 and odor-free; the subsequent biological effluent COD was ≤20 mg/L, ammonia nitrogen ≤1 mg/L and total phosphorus ≤0.2 mg/L. This case shows that the CDOF can serve as an important technical unit for landfill-leachate advanced treatment or standard-upgrading retrofit.

VI. Terminal effluent assurance: give priority to the 'KFM activated-media filter'

When wastewater, after front-end deoiling, flotation or oxidation treatment, still needs further reduction of residual oil and fine suspended solids, the KFM activated-media filter can be used as the terminal assurance unit. The KFM activated media, modified to be super-hydrophilic, features high filtration precision, low resistance, strong anti-fouling capability, easy cleaning and long service life, and is suitable for oilfield produced water, refinery and chemical wastewater and other scenarios requiring fine filtration.

Under the conditions of influent oil content ≤50 ppm and SS ≤50 mg/L, the KFM filter outlet can reach oil content ≤6 ppm, SS ≤2 mg/L and median particle size ≤1.5 μm. For projects with high requirements for subsequent reuse, reinjection, advanced treatment or compliant discharge, the KFM can serve as an important guarantee for stable effluent.

Conclusion

The key to complex industrial wastewater treatment is not simply selecting a certain piece of equipment, but determining the combined process according to water-quality characteristics and treatment objectives. High-oil wastewater needs coalescing deoiling and the CDFU for rapid oil reduction; extremely high-oil acidic water needs the CDFU and KHC to achieve synergistic deep separation; high-shock oil-depot wastewater needs filtration and coalescing deoiling to ensure low-oil effluent; composite oilfield wastewater needs the CDFU, CDOF and KFM to work together; landfill leachate needs the CDOF for COD reduction, decolorization and deodorization; and terminal fine-filtration scenarios can rely on the KFM to ensure stable effluent.

The value of SINOKLE's combined technology lies precisely in its ability to perform modular configuration according to different scenarios, and through the process philosophy of 'front-end load reduction, mid-stage intensification and back-end assurance', to achieve the synergistic improvement of multiple indicators such as oil, suspended solids, COD, chromaticity and odor, providing more stable, efficient and implementable systematic solutions for difficult industrial wastewater treatment.