Continuous electrophoretic separation of submicron-microplastics from freshwater

Abstract

Anthropogenic and natural weathering processes have produced submicron microplastics (MPs), an emerging contaminant. Due to small size, the treatment of submicron plastics particles by membrane processes requires small cutoff membranes, which necessitates great pressure gradient and suffers from clogging. The present study aims to develop an electrophoretic separation system for the separation of negatively charged submicron plastics particles from water. An electric field was supplied to produce an electrostatic force to counter the drag force in the permeation stream, thereby, preventing submicron plastics particles from entering the permeate. The critical electric field (E_c) for complete particles removal was estimated based on the dilute-to-influent flow rate ratio (q_d), zeta potential, and size of submicron plastics particles. The result showed that at steady-state, particle removal could reach 99 % at E > E_c at q_d = 0.5. The distribution of plastics particles during electrophoretic separation was analyzed considering electrophoresis and particle deposition. The particle removal efficiency can be modelled by hydraulic condition and critical electric field. Finally, the engineering aspects such as long-term operation, electrode degradation and influence of coexisted constituents were evaluated. The operation cost of electrophoretic separation was calculated to be USD 0.48/m³, which is cost-effective at small scales compared to conventional membrane processes.