Oilfield Wastewater Treatment Process

Oilfield wastewater treatment is an important environmental step in oil extraction and refining, with complex water quality and high treatment difficulty. Such wastewater typically contains high concentrations of free oil (up to 5,000 mg/L), emulsified oil, suspended solids and heavy metals, and is characterized by complex composition, large quality fluctuations and high environmental risk. Conventional processes such as API separators plus air flotation suffer from low efficiency (only 60%-85% oil removal), large footprints and hazardous oily sludge, making it hard to meet ever stricter requirements (e.g. the A1 reinjection standard requires oil ≤5 mg/L).

Conventional Treatment Processes and Their Drawbacks

• Gravity settling
  Large tanks are used for static separation; settling takes 50-70 hours, separation of emulsified oil (<10 μm) is poor, and effluent oil content is usually >50 mg/L.
  The open design allows acid gases to escape, endangering the environment and personnel health, and requires a large footprint with frequent manual cleaning.
  

• Cyclonic de-oiling
  Relies on centrifugal force, but removal of emulsified oil whose density is close to water (e.g. 1-5 μm) is below 30%, and tolerance to water quality fluctuations is poor.
  Cyclones clog easily and require high-pressure pumps, resulting in high energy consumption and frequent maintenance.
  

• Air flotation plus inorganic ceramic membrane
  Membrane filtration is precise (down to 0.1 μm), but membrane fouling is severe, requiring frequent acid/alkali cleaning and generating secondary waste liquid.
  Capital cost is high (about three times that of physical methods), water recovery is below 60%, and high-pressure operation consumes significant energy.
  

• Common drawbacks:
  Reliance on chemicals (e.g. PAC/PAM) with annual chemical costs exceeding one million yuan and hazardous sludge generation;
  Low automation; conventional flotation bubbles are large (300-1,000 μm), so oil droplet capture efficiency is below 50%.

SINOKLE has innovatively developed the CDFU cyclonic dissolved gas flotation plus KFM active filter media process, which uses micro/nano bubble physical demulsification and nano-scale filtration to achieve single-stage oil removal >95% and effluent oil ≤5 ppm with no chemical addition — an efficient and environmentally friendly solution for oilfield wastewater.

A typical treatment scheme is shown below:

• Pretreatment stage
  Three-phase separator: rapidly separates free oil, solids and wastewater, handling influent with oil content ≤5,000 mg/L
  

• Core treatment process
  CDFU cyclonic dissolved gas flotation:
  • Physical demulsification with 5-30 μm micro/nano bubbles
  • Single-stage oil removal >95%, retention time <5 minutes
  • No chemical addition, sludge reduced by 90%
  KFM active filter media filter:
  • 1 μm filtration precision, effluent oil ≤5 ppm
  • Silicate-based modified filter media with a 15-year service life
  • Fully automatic backwash (5 minutes every 24 hours)
  

• Advanced treatment (optional)
  CDOF multiphase catalytic oxidation: treats refractory organics with COD removal >80%
  Modified inorganic membrane: suitable for reinjection water in ultra-low permeability reservoirs (A1 standard)
  

• Process comparison
  | Indicator | Conventional process (flotation + walnut shell) |CDFU +KFM process |
  |---------------|----------------------|-------------------|
  | Effluent oil | ≤50 mg/L | ≤5 mg/L |
  | Footprint | 1,000 m² (100 m³/h) | 42 m² (skid-mounted) |
  | Cost per ton of water | ≥CNY 1.5 | CNY 0.3 |
  | Sludge generation | Hazardous sludge 5 t/day | 0.5 t/day (non-hazardous) |
  

• Typical application cases:
  Changqing Oilfield: capacity 4,600 m³/d, influent oil ≤5,000 mg/L, effluent ≤10 mg/L