Colloidal fouling in forward osmosis: Role of reverse salt diffusion

Chanhee Boo, Sangyoup Lee, Menachem Elimelech, Zhiyong Meng, Seungkwan Hong

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182 Citations (Scopus)


Colloidal fouling behavior in forward osmosis (FO) was investigated, focusing on the role of reverse salt diffusion. Two suspensions of silica nanoparticles, with average particle diameters of 24 and 139nm, were used as model colloidal foulants. To verify the effect of reverse salt diffusion on the colloidal fouling behavior, NaCl and LaCl 3 were employed as draw solutions because they exhibit different reverse diffusion rates. Our results suggest that in colloidal fouling of FO, salts diffuse from the draw to the feed solution and accumulate within the colloidal fouling layer that forms on the membrane surface. The accumulated salts result in a marked acceleration of cake-enhanced osmotic pressure (CEOP), which reduces the net osmotic driving force for permeate water flux. Fouling was not observed with the small, 24-nm particles because of the lack of substantial cake formation, but was notable for the 139-nm particles and for a feed containing a mixture of the 24 and 139nm particles. Our findings further indicate that colloidal fouling is enhanced under solution conditions (ionic strength and pH) within the colloidal cake layer that promote aggregation or destabilization of the silica particles. Colloidal fouling reversibility was also examined by varying the cross-flow velocity during the FO fouling runs. We showed that in the absence of colloidal particle destabilization/aggregation, the permeate flux during colloidal fouling in FO recovered almost completely when the cross-flow velocity was increased from 8.5 to 25.6cm/s. Our results suggest that reverse salt diffusion in FO is a key mechanism that controls colloidal fouling behavior as well as fouling reversibility. Therefore, minimization of reverse salt diffusion through the selection of proper draw solutes and optimization of FO membrane selectivity are important for minimizing colloidal fouling as well as enhancing FO operation efficiency.

Original languageEnglish
Pages (from-to)277-284
Number of pages8
JournalJournal of Membrane Science
Publication statusPublished - 2012 Feb 15

Bibliographical note

Funding Information:
This research was supported by the World Class University (WCU) program (Case III) through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology ( R33-10046 ).


  • Cake-enhanced osmotic pressure (CEOP)
  • Colloidal fouling
  • Forward osmosis
  • Fouling reversibility
  • Reverse salt diffusion

ASJC Scopus subject areas

  • Biochemistry
  • General Materials Science
  • Physical and Theoretical Chemistry
  • Filtration and Separation


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