Understanding of low osmotic efficiency in forward osmosis: Experiments and modeling

Jincai Su, Tai-Shung Chung*, Bradley J. Helmer, Jos S. de Wit

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


This study discloses the critical factors that result in the low osmotic efficiency in forward osmosis (FO). Specifically, dual-layer hollow fiber membranes are prepared with newly-synthesized cellulose acetate propionate (CAP) as the outer active layer and commercial cellulose acetate (CA) as the inner sublayer. By carefully analyzing the hollow fiber cross section images, the porosity of the sublayer is found to be nonuniformly distributed at different locations. Viewing the membrane matrix as three consecutive layers, i.e., the active layer, the sublayer and the interface between them, the draw solute concentration profiles within each layer, the osmotic pressure gradients across each layer, and the transport resistance of each layer are determined. One interesting observation is that the active layer of the CAP-CA hollow fibers creates much larger resistance than the interface and the sublayer, indicating that the low osmotic efficiency (i.e., low water flux) is mainly due to the low water permeability of the active layer while internal concentration polarization (ICP) within the sublayer is less important. For any membranes, the active layer-sublayer interface also creates certain transport resistance. These findings provide a valuable reference for the understanding of FO and the design of advanced FO membranes.

Original languageEnglish (US)
Pages (from-to)156-165
Number of pages10
StatePublished - Mar 5 2013


  • Concentration profile
  • Forward osmosis
  • Osmotic efficiency
  • Transport resistance
  • Water flux

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Mechanical Engineering
  • Chemistry(all)
  • Materials Science(all)
  • Water Science and Technology


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