New insights into the relationship between draw solution chemistry and trace organic rejection by forward osmosis

Authors

Lei Zheng, University of Technology SydneyFollow
William E. Price, University of WollongongFollow
James A. McDonald, University of New South WalesFollow
Stuart J. Khan, University of New South WalesFollow
Takahiro Fujioka, Nagasaki UniversityFollow
Long D. Nghiem, University of Technology Sydney, Nguyen Tat Thanh UniversityFollow

RIS ID

136647

Publication Details

Zheng, L., Price, W. E., McDonald, J., Khan, S. J., Fujioka, T. & Nghiem, L. D. (2019). New insights into the relationship between draw solution chemistry and trace organic rejection by forward osmosis. Journal of Membrane Science, 587 117184-1-117184-10.

Abstract

This study elucidates the impact of draw solution chemistry (in terms of pH and draw solute species) and membrane fouling on water flux and the rejection of trace organic contaminants by forward osmosis. The results show that draw solution chemistry could induce a notable impact on both water flux and TrOCs rejection. In addition, the impact was further influenced by membrane fouling. The reverse flux of proton (or hydroxyl) could alter the feed solution pH, which governed the separation of ionisable TrOCs. In addition, charged compounds generally exhibited higher rejections than neutral ones by the clean membrane. Electrostatic interaction, rather than size exclusion, was therefore the dominant rejection mechanism for most compounds. There was also a weak correlation between rejection and molecular sizes of the 43 TrOCs. Compared with Na+, Li+ with a larger hydrated radius showed a significantly lower reverse salt flux, resulting in a lower ionic strength and therefore a stronger electrostatic interaction. A fouling cake layer consisted of low molecular weight neutral organics could also affect TrOC rejection due to pore blockage and cake-enhanced concentration polarisation.