Nanopore-based electrokinetic purification of oil-in-water emulsions with temperature and pH modulation

Abstract

Abstract Efficient purification of oil-in-water emulsions is significant for protecting global water resources. Nevertheless, the traditional passive technologies for handling oil-in-water emulsions suffer from the drawback of low cost-effectiveness due to the use of robust filtration membranes. In our previous research, an active electrokinetic-based oil droplet filtration technique was developed that relied on the negative dielectrophoretic phenomenon induced by the huge difference between the dielectric properties of oil and water. However, the effects of the temperature and pH of wastewater on the electrokinetic filtration efficiency of oil droplets have never been clarified. In the present work, a multi-physical theoretical model of electrokinetic purification of oil-in-water emulsions with modulation of temperature and pH is constructed. The dimensionless ratio of dielectrophoretic force over hydrodynamic (HD) force on an oil droplet is an essential criterion for its dynamic behavior, and it exhibits a positive correlation with purification effectiveness of oil-in-water emulsions. From numerical modeling, the magnitude of the dielectrophoretic force to HD force ratio on an oil droplet is enhanced by decreasing temperature, increasing ion concentration and a neutral pH (pH = 7.0) of oily wastewater. Then, the critical direct current voltage for realizing successful oil droplet filtration through an insulated nanopore under electrokinetics is analyzed under different parameters, with the results indicating that the amount of energy required for purification of oil-in-water emulsions can be reduced by reducing the temperature and neutralizing the pH of the aqueous solution. This work offers a theoretical understanding of electrokinetic purification of oil-in-water emulsions, contributing to its development for industrial applications.