Deep Purification and Reuse Process for Oily Wastewater in the Petrochemical Industry

Petrochemical wastewater contains floating oil, emulsified oil, dissolved oil, and a large amount of refractory organic matter. Its treatment process must combine physical, chemical, and biochemical methods in order to achieve discharge compliance or reuse.

The first stage of the process is oil separation and equalization. The oily wastewater first enters a horizontal-flow or inclined-plate oil separator. In this unit, utilizing the density difference between oil and water, floating oil rises to the surface and is collected, while the water volume and quality are simultaneously homogenized. Subsequently, the effluent enters a dissolved air flotation (DAF) unit. Within the DAF unit, microbubbles released from dissolved air carry emulsified oil and fine suspended particles to the surface where they are skimmed off, thereby significantly reducing oil content and COD.

The DAF effluent then flows into a biological treatment system. This system typically employs either a hydrolysis-acidification plus aerobic activated sludge process or a biological contact oxidation process to efficiently degrade dissolved organic matter. The biological treatment tank is followed by a secondary clarifier, where sludge-water separation takes place. To further meet reuse or stringent discharge standards, the clarified effluent passes through multi-media filtration and activated carbon adsorption to remove residual suspended solids and trace organic compounds.

The critical advanced purification unit adopts a dual-membrane process combining UF and RO. Acting as pretreatment for the RO, the UF almost completely rejects suspended solids, colloids, and bacteria. The UF permeate then enters the RO unit, where desalination and removal of small-molecule organic substances take place. The RO permeate can be reused as circulating cooling water or boiler makeup water, while the small volume of concentrate is either discharged after meeting standards or sent to a concentrate treatment system. Our equipment integrates oil separation, DAF, and fully automatic dual-membrane units, helping petrochemical enterprises achieve wastewater volume reduction and resource recovery.