Recovering crude oil instead of sludge: the economics of chemical-free CDFU flotation

In petrochemical, oilfield and power generation service, oily wastewater treatment has long sat in an uncomfortable position between compliance and economics. A plant can pay for chemicals, pay again for hazardous-waste disposal, and still carry the risk of an environmental violation. As resource value becomes prominent and regulations tighten, recovering and recycling value from the wastewater has moved from a nice-to-have to a design objective.

SINOKLE approaches this with its independently developed CDFU cyclonic dissolved gas flotation technology. It is a compact, sealed and pressurised flotation design that avoids the traditional route of treating pollution with chemicals. Through the purely physical integration of a cyclonic centrifugal field and micro-bubble dissolved air flotation, it purifies water and turns what was waste into a resource.

What chemical flotation costs beyond the reagent bill

Traditional chemical flotation relies heavily on flocculants and demulsifiers. Two side effects follow the separation. First, the separated waste oil is degraded in quality and carries high water content from the chemical admixture, which makes direct reuse difficult. Second, the process generates large amounts of oily chemical sludge classified as hazardous waste, expensive to dispose of and carrying environmental risk.

Both costs are easy to overlook at the design stage because they appear in different budgets from the treatment plant itself. They are also the reason a cheaper flotation unit can end up costing more per tonne of water.

The physical route and what it delivers

The CDFU technology uses a high-efficiency dissolved-air release system that produces ultra-fine bubbles concentrated at 5–30 µm, with D50 of 25 µm or less. In the patented cyclonic field, these bubbles collide and adhere at high speed with oil droplets that the centrifugal action has already concentrated, completing physical demulsification and separation with no chemical addition at all.

Two outcomes follow. On resource recovery, physical separation preserves the purity of the recovered oil, with water content stably controlled at a low level, below 10% depending on conditions. Such waste oil can be re-refined directly or used as feedstock, which changes its value from a disposal liability to a saleable stream. On hazardous waste, the generation of oily chemical sludge is prevented outright, saving thousands of yuan per ton in disposal costs and removing the related storage, transport and compliance obligations.

Turning a cost centre into a value line

Adopting CDFU shifts oily wastewater treatment from a pure environmental cost to a segment with measurable returns.

Direct resource revenue appears in scenarios such as electric-desalting draw-off water and oilfield produced water, where single-stage oil-removal efficiency above 90% recovers large amounts of crude oil. At a CNPC petrochemical company's electric-desalting wastewater project, the purely physical coalescing oil remover plus CDFU process achieved considerable high-quality waste-oil recovery and direct economic benefit.

Operating cost is low by design. Hydraulic retention time is as short as 1-3 minutes, gas consumption is only 2%-3% of treated water, and energy use sits far below traditional flotation. The compact skid design reduces footprint to one-third of conventional DAF, lowering both capital and operating costs.

Maintenance is also lighter. The equipment is mainly static, with no vulnerable parts such as mechanical scrapers, runs fully automatic and enclosed, and has strong shock resistance. Maintenance intervals extend and the labour and spares behind them shrink accordingly.

Field evidence across very different sites

The performance has been validated in demanding industrial projects in China and worldwide, from CNPC Sichuan Petrochemical and Sinopec Cangzhou Petrochemical to overseas work such as the Sierra Leone heavy-oil power plant. In each case the outcome was stable compliance plus a tangible resource return, which is a stronger claim than compliance alone.

Boundaries to respect

The technology is a separator, not an oxidiser. It removes free and emulsified oil and suspended solids; it does not remove dissolved organics, and it does not desalinate. Where a reuse standard demands low dissolved COD, a downstream catalytic oxidation stage is still required. Water content of recovered oil also depends on conditions, so the below 10% figure should be confirmed against the specific feed rather than assumed.

As the dual-carbon strategy and circular-economy model advance, technological innovation is the practical way to resolve the conflict between environment and benefit. A process that keeps oil out of the sludge and puts it back into the product pool does that with the least chemical complexity, which is why SINOKLE builds its oily wastewater line around it.

For a refinery weighing the two routes, the comparison fits on one page. Chemical flotation has a lower equipment price and a predictable effluent number, but it converts oil into hazardous waste and pays disposal on every tonne. The physical route has a higher equipment price, recovers saleable oil and carries almost no sludge obligation. Once the sludge disposal line and the recovered oil value appear in the same table, the ranking usually reverses, and it reverses further as disposal charges rise.