Numerical simulation of electrokinetic desalination using microporous permselective membranes

A new scheme for parallelization of microchannels for ion concentration polarization-based seawater desalination is proposed. In the proposed system, microchannels/micropores are paralleled only in ion-selective membrane region and all other parts are simply merged. A two-dimensional simulation model is developed to study performances of such a system, by calculating the salt removal ratio (SRR) and the average velocity of fluid, under varied working conditions. Our results show that SRR >98% for seawater salinity (realizing drinkable water) is achievable. It is found that a stronger cross membrane voltage strengthens electrokinetic flow of the second kind (EOF2) and increases both SRR and flow velocity. Increasing pressure promotes fluid flow but decrease SRR and EOF2 significantly when the ion depletion zone is destroyed. Volumetric energy consumption and energy per ion removal (EPIR) were also characterized under varied electric field and pressure conditions. Energy consumption as low as 12.82 kWh/m3 was realized to convert seawater (salinity ~500 mM) to the desalinated water (salinity ~10 mM) at a flow speed of 0.56 mm/s. The overall cost of water for such a process was estimated as 2.08 $/m3, which is competitive for small-scale desalination applications.