Removal of organic contaminants by RO and NF membranes

Yeomin Yoon, Richard M. Lueptow

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170 Scopus citations


Rejection characteristics of organic and inorganic compounds were examined for six reverse osmosis (RO) membranes and two nanofiltration (NF) membranes that are commercially available. A batch stirred-cell was employed to determine the membrane flux and the solute rejection for solutions at various concentrations and different pH conditions. The results show that for ionic solutes the degree of separation is influenced mainly by electrostatic exclusion, while for organic solutes the removal depends mainly upon the solute radius and molecular structure. In order to provide a better understanding of rejection mechanisms for the RO and NF membranes, the ratio of solute radius (ri,s) to effective membrane pore radius (rp) was employed to compare rejections. An empirical relation for the dependence of the rejection of organic compounds on the ratio ri,s/rp is presented. The rejection for organic compounds is over 75% when r i,s/rp is greater than 0.8. In addition, the rejection of organic compounds is examined using the extended Nernst-Planck equation coupled with a steric hindrance model. The transport of organic solutes is controlled mainly by diffusion for the compounds that have a high ri,s/r p ratio, while convection is dominant for compounds that have a small ri,s/rp ratio.

Original languageEnglish
Pages (from-to)76-86
Number of pages11
JournalJournal of Membrane Science
Issue number1-2
StatePublished - 15 Sep 2005

Bibliographical note

Funding Information:
This work was supported by National Aeronautics and Space Administration (NASA). The authors thank Hydranautics Inc. and Toray Industries Inc. for their donation of membrane samples. The authors also thank Richard Neal for his help in performing a number of rejection measurements.


  • Membrane pore radius
  • Nanofiltration
  • Organic compounds
  • Reverse osmosis
  • Water treatment


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