Oily Wastewater Treatment: The Real Headache Is Not "Too Much Oil" but "Oil That Is Too Fine" — Inside the Industry's Emulsified-Oil Dilemma
Everyone in the environmental protection field knows that oily wastewater treatment is a tough nut in the industrial wastewater sector. But anyone who has actually worked on site understands that the hardest part is not the visible floating oil — you can always skim it off or scoop it away. What really gives people a headache is the emulsified oil: invisible, untouchable, and impossible to get rid of.
What is emulsified oil? Simply put, the oil droplets have been "shattered" into micron or even sub-micron size and are evenly dispersed in the water. To the naked eye the water looks clear, yet the test results are startling. Such droplets are usually coated with a layer of surfactant or solid particles, forming a stable emulsified system that conventional gravity settling and simple oil-separation tanks simply cannot handle.
Why is emulsified oil so hard to treat?
The first reason is that the particle size is too small. Conventional floating oil droplets are tens to hundreds of microns in diameter and can be separated with an oil-separation tank or simple air flotation. Emulsified oil, however, is typically 1–5 microns, or even less than 1 micron. With droplets this small, Brownian motion is faster than their settling velocity — so how are they supposed to settle?
The second reason is high stability. The active substances on the surface of emulsified oil act like a protective shell, preventing droplets from colliding and coalescing with one another. The traditional approach is to add demulsifiers and coagulants, chemically "smashing" this shell. But the problem is: add too much agent and you produce large amounts of water-laden waste oil with high disposal costs; add too little and demulsification is incomplete, so the effluent fails to meet standards.
The third reason is complex operating conditions. Take electric desalting wastewater from the refining industry: the influent oil content can reach tens of thousands of milligrams per litre, and the water may contain dispersed oil, emulsified oil, and entrained catalyst particles and various organics. Conventional DAF (dissolved-air flotation) requires a residence time of 15 to 40 minutes, has a large equipment footprint and high energy consumption, and its removal efficiency for emulsified oil is often only 60% to 85% — leaving the "stubborn leftovers" for downstream to worry about.
The Ceiling of Common Industry Solutions
The mainstream solutions for oily wastewater on the market today fall roughly into several categories:
The first is the chemical method, adding coagulants such as PAC and PAM together with air flotation or sedimentation. The advantage is that it is mature; the disadvantages are the continuous consumption of chemicals, the generation of large amounts of chemical sludge, and limited effectiveness on highly emulsified wastewater.
The second is conventional DAF, which uses large bubbles (100–300 microns) that attach to oil droplets and float them up. The problem is that the bubbles are too large, so the probability of collision with tiny emulsified oil droplets is low; chemicals must be added to assist, otherwise the oil removal efficiency drops sharply.
The third is membrane filtration, which is indeed highly precise, but suffers from serious membrane fouling, high operation and maintenance costs, rapid flux decline in oily applications and frequent cleaning.
In short, the industry has long been compromising between "precision" and "cost". Want high precision? Then you need chemicals, membranes and extra process stages. Want low cost? Then you accept a compromise on effluent targets.
Is there a solution that lets you have your cake and eat it too?
SINOKLE has been deeply engaged in oily wastewater treatment for more than a decade and offers an answer worth noting: replace large bubbles with ultrafine bubbles, and replace chemical agents with a purely physical method.
SINOKLE's high-emulsification oily wastewater treatment project at a refinery (the image on the right compares influent and effluent results)
SINOKLE's Core Product CDF Uthe cyclonic dissolved-air flotation unit creatively combines cyclonic centrifugal separation with dissolved-air flotation technology. It generates microbubbles only 5–30 microns in diameter, with a median of about 25 microns — a scale that happens to collide efficiently with and adhere to 1–10 micron emulsified oil droplets. Conventional air flotation bubbles, by contrast, are often over a hundred microns and "pass by" the emulsified oil without capturing it.
Even more important,CDF Uachieves demulsification and oil removal by purely physical means, without adding any chemical agent throughout the process. No chemicals means no chemical sludge, and the separated oil is water-free and can be recovered and reused directly. The single-stage oil removal efficiency exceeds 90%, the residence time is only 1 to 5 minutes, and the equipment footprint is only a fraction of that of conventional DAF.
For wastewater with a particularly high degree of emulsification, SINOKLE also offers the KHC high-efficiency coalescing oil separator as an "outpost" — using special fibrous packing to capture tiny oil droplets so that they coalesce into large droplets at the fibre junctions and separate naturally, with a coalescing precision down to 0.1 microns. The combined "coalescing +CDFU" process first coalesces and then floats, applying two physical barriers that strip the emulsified oil away layer by layer.
Tightening Environmental Policy Forces Technology Upgrades
In recent years, with strict enforcement of water pollution prevention regulations and continuously tightening discharge standards across regions, the pressure to meet standards for oily wastewater has grown. In some key river basins and coastal areas in particular, discharge standards are now close to surface-water requirements. The era of "good enough" is over — now even the slightest shortfall is unacceptable.
Against this background, SINOKLE's purely physical solution is being accepted by more and more enterprises. From multiple refining and chemical projects of PetroChina and Sinopec in China to overseas oilfields in Congo, Africa; from electric desalting wastewater to fracturing flowback fluid, SINOKLE has proven through real projects that oily wastewater treatment does not have to rely on "dumping in chemicals" — technological innovation can achieve high efficiency, low cost and zero secondary pollution at the same time.
The industry's pain points are there for all to see, and the solution is already on its way. The key question is: are you willing to try a different approach?
