Fast swirl–coalescence filtration: Alternative to conventional inclined plate–air flotation for refinery sewage treatment

Efficient oil–solid removal from refinery sewage, especially highly concentrated electric desalting sewage, is key to ensuring the stability of subsequent biochemical treatment processes and meeting the sewage purification standards. The conventional inclined plate–air flotation process, which relies on chemical flocculation, is unable to meet the pretreatment requirements owing to the continuously increasing levels of petroleum pollutants and suspended substances (SSs) in refinery sewage. Herein, a physical oil–solid removal process, named fast swirl–coalescence filtration, is proposed and verified via pilot tests. This technology can reduce the average oil concentration of refinery and electric desalting sewage to 11.08 and 19.62 mg/L, with average oil removal efficiencies of 96.47 % and 99.89 %, respectively. Further, the average SSs concentration can be reduced to 16.47 and 70.90 mg/L, with average suspension removal efficiencies of 87.46 % and 91.09 %, respectively. Compared with the conventional treatment process, the proposed treatment process reduces the equipment footprint by 75 %, eliminates the use of chemical agents, and shows good adaptability to incoming sewage fluctuations, providing a new strategy for green and efficient treatment of refinery sewage.