Study on the unique separation effect of emulsion in the stirring-induced turbulent flow field

Abstract

Much attention has been gained to treat organic pollution dominated by oil pollutants in water with the frequent discharge of wastewater in industries. Liquid–liquid emulsion is a typical existence form of water and oil pollutants. The relative stable flow field is a necessary condition to separate the emulsion, while turbulence of the flow field is required for homogeneous mixing. For centuries, stirring-induced turbulent flow has been used for mixing, with a limited number of separation cases achieved by the stable part of the container at low Reynolds numbers (Re). In this study, the separation of liquid–liquid emulsions in a fully turbulent system for Reynolds number values above 10,000 was observed for the first time. Besides the turbulent flow influenced by the stirring speed, the additional dispersed phase, which was the same as the emulsified dispersed phase, played a critical role in the separation performance. The turbidity of oil-in-water emulsion could be decreased to less than 5 NTU (nephelometric turbidity unit) from 500 NTU under the optimal conditions in this study, with a separation efficiency of over 99%. This peculiar and wonderful characteristic of the turbulent flow and the study of the parameters and constraint conditions for separation may extend the application field of the turbulent flow field from conventional mixing to oil pollutants separation from water in environmental engineering.