Ship Oily Wastewater at 60 m3/h: What a Two-Stage CDFU Skid Delivers for Port Treatment Projects
Ships generate their own wastewater problem as they work. Ship oily wastewater is wastewater generated during ship operation that contains grease, fuel residues, lubricating oil and other pollutants, mainly originating from engine rooms and cargo holds, and covering oily tank washing water, engine room oily water and oily ballast water. Its composition is complex: hydrocarbon residues and solid particles from fuel combustion, lubricating oils from various mechanical equipment, and edible oils and paints generated during operation. It is generally severely emulsified, so traditional oil interception and gravity sedimentation processes struggle to meet standards, while chemical treatment produces large amounts of hazardous waste and treatment costs are high. Port reception facilities inherit all of that difficulty, compressed into a variable, event-driven flow.
The pure-physical core: CDFU
To solve this problem, SINOKLE adopted a pure physical treatment solution centered on its CDFU (Cyclonic Dissolved Gas Flotation Unit), which organically integrates cyclonic centrifugal separation, a new generation of dissolved air technology and high-efficiency flotation, using micro-nano bubbles to achieve efficient demulsification and oil removal and stable discharge up to standard. Thanks to its specially designed flotation method, the technology greatly improves flotation efficiency, shortens residence time, and achieves rapid removal of oil and suspended solids. The physics is the same logic that works ashore: spin the water, dissolve gas into it under pressure, release micro-nano bubbles that grab the droplets, and float the load away fast.
Five advantages that matter on a deck
The process has significant advantages, and each one earns its place in a marine context. First, pure physical demulsification and separation with high and reliably stable oil removal efficiency; the recovered waste oil creates economic benefits, with no secondary pollution and no oily hazardous waste generated. Second, the amount of scum is reduced by more than 1/3, lowering secondary treatment costs. Third, closed operation under pressure, with no hydrogen sulfide or oil vapor leakage, ensuring a safe and friendly site environment, which matters doubly inside an enclosed shipboard or pontoon space. Fourth, single-stage residence time of less than 5 minutes, small footprint, fully automatic operation, easy operation and maintenance, short construction period, and possible online implementation. Fifth, strong shock resistance, able to adapt to large water quality fluctuations. A reception facility never knows what the next vessel will pump ashore, so shock tolerance is not a nice-to-have, it is the entry ticket.
How the two-stage process runs
In the treatment process, ship oily wastewater passes through two-stage CDFU oil removal. Under the swirl action in the tank, the wastewater fully contacts the ultrafine bubbles generated by dissolved air; pollutants are attached, demulsified and aggregated, then float up and are discharged to the waste oil collection tank, while waste residue enters the sludge pit. Under normal water quality, neither stage needs flocculant; when emulsification is severe, only the second stage adds a small amount of flocculant as appropriate. The second-stage effluent enters the downstream process after being tested up to standard by an oil-in-water analyzer. Nitrogen is used for gas injection in both stages, and the tail gas is treated by a tail gas destruct unit before discharge, ensuring stable and compliant treatment results. The nitrogen choice is a quiet safety decision: in closed tanks, air plus hydrocarbon vapor is a combustible mixture waiting for a spark, and nitrogen blanks that risk out.
Automation without a crew
The entire system uses PLC or DCS fully automatic control; closed operation under pressure involves no safety or environmental risks. The dissolved air pump supports automatic and manual start modes and is equipped with automatic protection programs; effluent, oil discharge, exhaust and other stages are all automatically regulated, making operation and maintenance convenient. For port facilities that run intermittent, surge-driven duty rather than steady-state loading, an automatically regulated train that starts, treats, discharges and protects itself between events is the difference between a manageable utility and a constant staffing burden.
A port project in numbers
A project example at a port in Guangdong with a treatment capacity of 60 m3/h shows how the system lands in practice. The complete set of equipment is integrated on one skid containing two CDFU reaction tanks and one stabilization tank, covering a total area of only 30 m2. The influent oil content and suspended solids were both about 1000 mg/L; after two-stage CDFU treatment, the oil content dropped below 30 mg/L and the suspended solids below 60 mg/L; after subsequent downstream treatment, compliant discharge was achieved, verifying the efficiency and practicality of this process. Those figures compress the whole argument: one skid, thirty square meters, a thousand milligrams per liter of oil coming in, and a discharge that clears the bar. For port authorities planning reception capacity under tightening maritime discharge rules, a two-stage CDFU skid of this class is the reference architecture to compare every proposal against.