Oily Wastewater Treatment Process for Ships, Ports and Terminals
Ship, port and terminal oily water is the wastewater containing grease, fuel residues and lubricating oils generated in ship operation, mainly from engine rooms and cargo holds, including oily tank washing water, engine-room oily water and oily ballast water. Its main components are: fuel combustion residues (unburnt hydrocarbons, solid particles), various lubricating oils (main engine oil, gearbox oil, etc.), oils/greases from processing, storage and transport (edible oil, paraffin, paint, etc.), and oily washing water and domestic sewage.
Such wastewater is heavily emulsified and difficult to treat with conventional oil separation or gravity settling, while chemical dosing generates large amounts of hazardous waste at high cost.
To tackle this problem, a technical scheme centred on CDFU cyclonic dissolved air flotation is adopted. The technology efficiently demulsifies and removes oil by purely physical means, achieving stable, compliant treatment and discharge of the oily water.
CDFU (Cyclonic Dissolved Gas Flotation Unit) technology organically integrates cyclonic centrifugal separation, a new generation of dissolved air technology and high-efficiency flotation separation. Using micro-nano bubbles generated by cyclonic action and dissolved gas, together with a specially designed flotation mode, it markedly raises flotation efficiency and shortens retention time, achieving rapid, efficient removal of oil and suspended solids.
Cyclonic dissolved air flotation CDFU workflow diagram
Core advantages of the process:
Purely physical demulsification: Efficient oil removal, stable and reliable; the recovered oil is reused, with no secondary pollution and no hazardous oily sludge, combining environmental and economic benefits.
Waste reduction and cost saving: Scum volume reduced by more than 1/3, less hazardous waste generated, low secondary treatment costs.
Safe and environmentally friendly: Closed pressurised operation prevents hydrogen sulphide and oil vapour leakage; friendly site environment.
Efficient and compact: Single-stage retention time <5 minutes, small footprint; fully automatic operation, easy O&M, short construction period, supports online implementation.
Stable and reliable: Strong shock resistance, tolerates large fluctuations in water quality.
Treatment flow:
The oily water undergoes two-stage CDFU treatment. In the CDFU tank, under the cyclonic action the oil is rapidly attached by the ultra-fine bubbles generated from dissolved air, demulsified, aggregated and floated up, discharging through the top oil outlet.
Normal operating condition: No flocculant in either stage; discharged oil goes to the waste oil tank and residue to the sludge pit.
Highly emulsified condition: No flocculant in the first stage; a small amount of flocculant is added to the second stage as needed; discharged oil goes to the waste oil tank and residue to the sludge pit.
The second-stage CDFU effluent is checked by an oil-in-water analyser and enters downstream processes once compliant. Nitrogen is used for inlet gas in both stages, and the tail gas is treated by a tail-gas destructor before discharge. The treated effluent stably meets the standard.
System control:
Fully automatic, closed pressurised operation with no safety or environmental risk.CDFU effluent, discharged oil, exhaust, gas make-up and dissolved-air system intake are all fully automatically controlled. The dissolved air pump has automatic/manual start modes and automatic protection programs. The skid uses PLC/DCS fully automatic control for easy operation and maintenance.
Application example:
A port project in Guangdong with a treatment capacity of 60 m³/h. The equipment is a single skid containing two CDFU reaction tanks and one stabilisation tank, occupying only about 30 m². The influent oil content is about 1000 mg/L and suspended solids about 1000 mg/L; after two-stage CDFU treatment, the oil content drops below 30 mg/L and suspended solids below 60 mg/L, followed by further treatment to achieve compliant discharge.
