Functional magnetic nanoparticles for enhancing ultrafiltration of waste cutting emulsions by significantly increasing flux and reducing membrane fouling

Waste cutting emulsions have high oil concentration, complex components, and strong stability, making them extremely difficult to dispose of. Efficient separation of oil and water is key to disposing of such emulsions. In this study, magnetic nanoparticles (MNPs) were applied in different ways to the membrane separation process to form four coupling processes for emulsion treatment. Compared to direct ultrafiltration, the four coupling processes showed improved performance in chemical oxygen demand (COD) rejection and flux for sample waste cutting emulsions. In particular, the flux of the optimal process was 83 LMH, which was 41.5 times greater than the control process. The interactions between MNPs and emulsions, such as coalescence, coating, and migration under a magnetic field, were also studied. We believe that the introduction of MNPs actively affected the membranes; the MNPs avoided direct oil-membrane contact via the coating of oil drops and a cake layer that formed on the membrane surface, which then enhanced ultrafiltration and improved flux significantly.