Difficult industrial wastewater treatment cannot be judged by a single total indicator; one must look at the form in which the pollutants exist. Take oily wastewater as an example: although both show "high oil content", the oil may be large free oil droplets, fine dispersed oil, or stable emulsified oil; although both show "high COD", part of it may come from easily biodegradable organics while another part may be refractory organics; although both show "high suspended solids", some particles settle easily while others are colloids or fine particles. Different pollutant forms require different treatment methods.

The core idea of SINOKLE's combined technology is to configure the process according to the pollutant form, rather than using a single device to treat all problems. For large free oil droplets, coalescing oil removal or hydrocyclone separation is preferred; for fine oil droplets and emulsified oil, CDFU (cyclonic dissolved-air flotation) is used to enhance capture and coalescence; for refractory organics, color and odor, the CDOF ozone advanced-oxidation flotation integrated unit is used for oxidative degradation; and for residual fine particles and trace oil droplets, the KFM active-media filter provides end-of-line assurance.

The first category of pollutants is free oil and large dispersed oil. These droplets are relatively large and are well suited to removal by coalescence, cyclonic and gravity separation. A front-end coalescing oil remover makes small oil droplets collide, adsorb, coalesce and grow on the surface of the coalescing material, making them easier to separate from water. The aim of this stage is not to complete all deep treatment at once, but to rapidly reduce the high oil load and protect the downstream units.

The second category of pollutants is fine dispersed oil and emulsified oil. These droplets are small and have a stable interface, so ordinary oil separation is ineffective and simple filtration tends to clog. CDFU, through its cyclonic flow field, micro-nano bubbles and coalescence action, gives fine oil droplets a higher collision frequency and stronger rising driving force. Once bubbles attach, the apparent density of the oil droplet drops and its rising velocity increases; as the droplets coalesce and grow, they become easier to separate. Therefore, CDFU is better suited to wastewater with a high degree of emulsification, fine oil droplets and obvious oil entrained in suspended solids.

The third category of pollutants is suspended solids, colloids and oil-bearing particles. These pollutants affect effluent turbidity and also raise the load on downstream filtration and oxidation systems. CDFU can remove part of the suspended solids by flotation, while KFM can further filter residual fine particles at the end of the line. For wastewater with high SS, removing suspended solids at the front end serves not only to lower the SS indicator but also to reduce fouling of downstream catalysts, media and membrane systems.

The fourth category of pollutants is dissolved refractory organics. These cannot be removed by ordinary oil removal or filtration and require advanced oxidation to break their molecular structure. CDOF, through ozone catalytic oxidation and enhanced mass transfer, promotes chain scission, ring opening and oxidation of refractory organics, while also improving color and odor. For landfill leachate, chemical wastewater, oilfield composite wastewater and similar scenarios, CDOF is the key unit for solving COD, color and odor problems.

The fifth category of pollutants is residual trace oil droplets and fine particles at the end of the line. After front-end oil removal and mid-stage oxidation, a small amount of fine pollutants may remain and cause effluent fluctuation. The KFM active-media filter acts as the end-of-line assurance unit, further reducing residual oil, SS and turbidity for more stable effluent. For projects involving reuse, reinjection, offshore discharge or entry into membrane systems, this end-of-line assurance is especially important.

Following this line of thinking, different wastewater scenarios can form different combined processes. For refinery electric-desalting and tank-farm black water, a "high-efficiency coalescing oil remover + two-stage CDFU" can be used, focusing on high oil content and emulsified oil. In a petrochemical project in Xinjiang, the influent oil content was ≤20000 ppm and the treated effluent oil content was ≤150 ppm, demonstrating the suitability of this route for high-oil refinery wastewater.

For coking acidic water, a "CDFU + KHC high-efficiency coalescing oil remover" can be used: CDFU first rapidly removes most of the oil and suspended solids, then KHC deeply coalesces and removes the fine emulsified oil. This route suits highly oily, strongly emulsified acidic water with great separation difficulty.

For oilfield produced water, fracturing flowback fluid and drilling waste liquid, "CDFU + CDOF + KFM" can be used: front-end CDFU removes oil and SS, mid-stage CDOF degrades refractory organics and improves color and odor, and end-of-line KFM stabilizes the effluent. After a Congo-Brazzaville oilfield project adopted this combined process, the effluent met offshore discharge standards with petroleum ≤0.5 ppm, turbidity ≤3 NFU, SS ≤3 mg/L and iron ≤0.15 mg/L.

For deep treatment of landfill leachate, CDOF can be emphasized: on the one hand it reduces COD through ozone catalytic oxidation, and on the other hand it simultaneously improves color and odor. In a Shiyan, Hubei leachate project, MBR effluent COD was ≤1300 mg/L; after CDOF treatment COD was ≤400 mg/L, color ≤30 and odor-free, and subsequent biological treatment further reached lower indicators.

In conclusion, the key to difficult industrial wastewater treatment is not simply stacking equipment, but configuring the stages according to pollutant form. Every pollutant has its most suitable removal method, and every treatment unit should shoulder a clear task. SINOKLE's combined technology realizes the systematic treatment and stable compliance of complex wastewater through the path of "identify pollutant form — determine treatment sequence — configure technology units — verify treatment effect".