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

Abstract

Efficient purification of oil-in-water emulsion is significant for protecting global water resource. Nevertheless, the traditional passive technologies for handling oil-in-water emulsion suffer from the drawback of low cost-effectiveness for using robust filtration membranes. In our previous research, an active electrokinetic based oil droplet filtration technique is firstly developed relying on a negative dielectrophoretic phenomenon induced by the huge difference between dielectric properties of oil and water. However, the effects of temperature and pH value of wastewater on the electrokinetic filtration efficiency of oil droplet have never been clarified. In the current work, a multi-physical theoretical model of electrokinetic purification of oil-in-water emulsion with thermal and pH modulation is constructed. The dimensionless ratio of dielectrophoretic force over hydrodynamic force on oil droplet is an essential criterion for its dynamic behavior, and it exhibits a positive correlation with purification effectiveness of oil-in-water emulsion. From numerical modelling, the magnitude of dielectrophoretic force to hydrodynamic force ratio on oil droplet is enhanced with a decreasing temperature, increasing ion concentration, and neutralized (pH=7.0) property of oily wastewater. Then, the critical direct current voltage for realizing successful oil droplet filtration through insulated nanopore under electrokinetics is analyzed under different parametric conditions, which indicates that the energy consumption of oil-in-water emulsion purification can be reduced by cooling down temperature and neutralizing pH value of aqueous solution. The current work offers a theoretical understanding of electrokinetic purification of oil-in-water emulsion, contributing to its development towards industrial applications.