Concentric ion concentration polarization desalination for efficient En-bloc preconcentration and desalination

Abstract

The techniques of focusing or separating test samples in water prior to usage, known as preconcentration or filtration (desalination) depending on whether the samples are being enriched in or removed from the solution, are basic yet essential processes in the fields of mechanical/biological/chemical engineering applications. Over the years, many strategies have been introduced to improve the technique, yet overcoming the dilemma of the degree of preconcentration/filtration versus the efficiency still proves to be challenging. Here, as a viable solution to mitigate this trade-off issue, we introduce a preconcentration/filtration technique utilizing ion concentration polarization (ICP) desalination, performed within a two-dimensional concentric geometry. Designed to provide the compensation for the pressure imbalance and minimizing undesirable solvent/solute fluxes between channels, this system is capable of operating under a large flow rate difference between preconcentrate and filtrate flows, and therefore is able to produce highly concentrated solution (up to 425-fold) and desalted solution with high water recovery (up to 99.765%), in addition to securing a high salt removal (>96.8%). Such achievement of the concentric ICP desalination is a clear outperformance of the previous one-dimensional ICP desalination systems (with juxtaposed membranes in one direction), which can obtain less than only 60-fold of preconcentration and 98% of water recovery. This structural modification strategy not only has enhanced the performance of the selected system for our experiment, but also suggests a new approach to improve the preconcentration/filtration/desalination capability of other techniques, mainly those of which are based on continuous channel flow.