Nanopore-based active oil droplet filtration under negative DC dielectrophoresis for oily wastewater treatment

Abstract

Efficient separation of oil droplets from oily wastewater is an essential task for handling the world water crisis and environmental pollution. However, existing passive oil/water separation technologies suffer from the drawbacks of relatively low separation efficiency and strict material requirements. We present an active dielectrophoretic oil/water separation technique without inducing further environmental contamination. Based on the non-uniform electric field generated through insulated nanopores under direct current (DC) voltage, an oil droplet experiences a negative dielectrophoresis (nDEP) force because of its weaker dielectric property compared with wastewater. Meanwhile, electroosmotic flow also occurs in oil/water separation devices due to the ion motion inside the electric double layer of the nanopore solid surface. Through developing a multiphysical model for immiscible oil/water flow under hybrid electrokinetic effects, the oil/water separation is investigated at different parametric conditions. Electrokinetic filtration of oil droplets through nanopores is successfully achieved when the nDEP force is dominant rather than the electroosmotic electrohydrodynamic (EHD) force for oil droplet movement. To enhance the oil/water separation rate, the relative strength between nDEP force and EHD force on an oil droplet is consolidated via increasing DC voltage, decreasing surface charge density, and optimizing the nanopore configuration. The designed active oil/water separation using DC-DEP offers significant potential for future oily wastewater treatment.