In recent years, ionic liquids have received increasing interests as an effective demulsifier due to their characteristics of non-flammability, thermal stability, recyclability, and low vapor pressure. In this study, emulsion formation and types, chemical demulsification system, the application of ionic liquids as a chemical demulsifier, and key factors affecting their performance were comprehensively reviewed. Future challenges and opportunities of ionic liquids application for chemical demulsification were also discussed. The review indicted that the demulsification performance was affected by the type, molecular weight, and concentration of ionic liquids. Moreover, other factors, including the salinity of aqueous phase, temperature, and oil types, could affect the demulsification process. It can be concluded that ionic liquids can be used as a suitable substitute for commercial demulsifiers, but future efforts should be required to develop non-toxic and less expensive ionic liquids with low viscosity, and the demulsification efficiency could be improved through the application of ionic liquids with other methods such as organic solvents.

Gas flotation for oily wastewater treatment is based on the attachment of gas bubbles to oil droplets to produce lighter aggregates that rise to the wastewater surface. It is a feasible, promising, and effective method for oily wastewater treatment due to its high separation efficiency with no secondary contamination, cost-effectiveness, and simple operation. This review focuses on separating oil from emulsions by gas flotation using microbubbles (MBs) and nanobubbles (NBs), which offer the advantages of small bubble size, large specific surface area, and slow rising velocity. The properties of different types of gas bubbles and their generation methods were discussed. Different gas flotation system designs and operational parameters were summarized for dissolved gas flotation, induced gas flotation, and electrolytic flotation (EF). The review illustrated that oil removal efficiency in MB- and NB-based gas flotation was affected by various factors including initial oil concentration, pH, temperature, flotation time, and oil droplet size.