Imaging of membrane concentration polarization by NaCl using 23Na nuclear magnetic resonance

Masoumeh Zargar, Ryuta Ujihara, Sarah J. Vogt, Johannes S. Vrouwenvelder, Einar O. Fridjonsson, Michael L. Johns*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


Forward osmosis (FO) and reverse osmosis (RO) membrane processes differ in their driving forces: osmotic pressure versus hydraulic pressure. Concentration polarization (CP) can adversely affect both performance and lifetime in such membrane systems. In order to mitigate against CP, the extent and severity of it need to be predicted more accurately through advanced online monitoring methodologies. Whilst a variety of monitoring techniques have been used to study the CP mechanism, there is still a pressing need to develop and apply non-invasive, in situ techniques able to produce quantitative, spatially resolved measurements of heterogeneous solute concentration in, and adjacent to, the membrane assembly as caused by the CP mechanism. To this end, 23Na magnetic resonance imaging (MRI) is used to image the sodium ion concentration within, and near to, both FO and RO composite membranes for the first time; this is also coupled with 1H MRI mapping of the corresponding water distribution. As such, it is possible to directly image salt accumulation due to CP processes during desalination. This was consistent with literature expectations and serves to confirm the suitability of 23Na MRI as a novel non-invasive technique for CP studies.

Original languageEnglish
Article number117868
Number of pages6
JournalJournal of Membrane Science
Publication statusPublished - 2020


  • Concentration polarization
  • Forward osmosis
  • Magnetic resonance imaging
  • Reverse osmosis
  • Sodium


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