Insights into the relation of crude oil components and surfactants to the stability of oily wastewater emulsions: Influence of asphaltenes, colloids, and nonionic surfactants

Large amounts of asphaltenes, colloids, and surfactants in the oily wastewater emulsions produced during the resource utilization of oily sludge make the treatment of oily wastewater emulsions difficult. In this study, the crude oil components were separated by solvent separation method, characterized by SEM, XRD, FT-IR, and EDS for crude oil components, suspended solids, and “oil-particulate aggregates”, and compared the emulsification performance of each crude oil component according to the oil–water wetting angle. In addition, the static stability and coalescence stability of different surfactant emulsions were determined, and the kinetic parameters of emulsion decomposition and oil–water interfacial film strength parameters were calculated based on the stability model of emulsion two-phase separation. The mechanisms of active components such as asphaltenes and colloids in crude oil and surfactants on the emulsion stability of oily wastewater were analyzed. It was found that the polar components in crude oil consisted of asphaltenes and colloids, and with the increase of asphaltenes and colloids, the oil–water wetting angle decreased significantly and the emulsion stability increased, and the emulsion stability of nonionic surfactants was better than that of cationic and anionic surfactants, among which octylphenol polyoxyethylene ether (10) (OP-10) had the best emulsion stability. The results of the study provide a theoretical basis for the demulsification and oil removal of oily wastewater emulsions.