Utilization of the Donnan effect for improving electrolyte separation with nanofiltration membranes

R. Levenstein, D. Hasson*, R. Semiat

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

165 Scopus citations


The possibility of utilizing the Donnan effect to enhance NaCl removal from a solution of a water-soluble organic dye (Procion Red H-E7B, ICI) using a nanofiltration membrane was examined. The increased salt removal is obtained by the addition of an ionized polyelectrolyte (Na salt of polyacrylic acid, PNa) having a molecular weight of 60,000 dalton. Salt rejection data and permeate flux were measured in three solution systems: NaCl-H2O, NaCl-H2O-dye and NaCl-H2O-dye-PNa. The solutions were fed through a parallel plate osmotic cell having an area of 200 cm2, fitted with an MPF-44 nanofiltration membrane. Polyelectrolyte addition was found to provide a substantial enhancement of salt removal. For example, chloride rejection in a binary system with a salt weight concentration of 1% was around 50% (i.e. permeate salt concentration is about half that of the feed). Addition of 4.4% PNa decreased the salt rejection to a negative value of -68%, signifying that permeate salt concentration was almost 1.7 times higher than the feed concentration. However, polyelectrolyte addition reduced permeate flux and induced a flux limiting phenomenon, similar to that commonly encountered in ultrafiltration. A simple two parameter model is presented which successfully correlates the salt rejection data measured in this work, as well as results reported in the literature. The model enables prediction of salt rejection in multi-ionic systems from data measured easily in a single salt system and can be usefully applied for quantifying NF processes utilizing the Donnan effect.

Original languageEnglish
Pages (from-to)77-92
Number of pages16
JournalJournal of Membrane Science
Issue number1
StatePublished - 24 Jul 1996
Externally publishedYes


  • Donnan effect
  • Nanofiltration
  • Polyelectrolytes
  • Salt rejection
  • Transport models


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