Continuous separation of submicron-scale oil droplets in aqueous electrolyte by electrophoretic migration

Abstract

Separation of tiny oil droplets, which is not readily achieved by conventional oily wastewater treatment, is becoming important in the petrochemical industries with regard to public health and the global environment. Herein, we report a continuous and filterless separation of submicron-scale oil droplets based on electrophoretic migration in a three-dimensional (3D) printed microfluidic free-flow electrophoresis (μFFE) device which is miniaturized system of conventional electrodialysis (ED). Microscale electrodialysis system with commercial ion exchange membrane (IEM) is proposed to control the dynamics of negatively (or positively) charged tiny oil droplets. We examined separation performance for various parameters, such as applied voltage, recovery ratio, flow velocity, solution concentration, and flow-channel dimension, with visualization of fluorescent oil droplets. Separation of several non-fluorescent submicron-scale oil droplets (e.g. gasoline engine, diesel engine, gear, and palm oils) were also investigated, including measurement of droplet diameters and surface charge (zeta potential). Future scale-up of the proposed microfluidic ED system will be a promising method for the treatment and relevant applications of industrial oily wastewater.