Role of surfactants in facilitating oil-solid separation in oily sludge treatment

Oily sludge is an inevitable by-product of the petroleum industry, characterized by both petroleum resources and hazardous waste. Surfactants, with their hydrophilic heads and hydrophobic tails, are extensively utilized in oily sludge treatment to remove crude oil adsorbed on solid particles. They create distinct interfaces between oil, water, and solid phases, disrupting sludge stability and allowing for solid separation through settling or stirring. However, the fundamental understanding of surfactant-based technologies in oily sludge treatment remains limited. Systematic research on the forces exerted by different surfactants and petroleum components during oil removal is lacking. This review summarizes the critical role of surfactants in both thermal washing and microemulsion-based washing methods for treating oily sludges. It provides a detailed categorization of various surfactant types and analyzes the factors influencing their efficiency in oil removal. Moreover, we also cover the elucidation of the oil removal mechanisms and corresponding molecular interactions underlying surfactant-based thermal washing and microemulsion-based washing methods in the oily sludge treatment process. The remaining challenges and future perspectives regarding the design and application of novel surfactant systems for oily sludge treatment are also discussed, which provides useful insights and guidance for future research directions. © 2024 Elsevier B.V.