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Published on: February 13, 2016
Identifying the fouling behavior of forward osmosis membranes exposed to different inorganic components with high
Huihui Zhang1, Xudong Wang1, Lei Wang2
1Research Institute of Membrane Separation Technology of Shaanxi Province, Key Laboratory of Membrane Separation of Shaanxi Province, Key Laboratory of Northwest Water Resources, Environmental and Ecology, Ministry of Education, Key Laboratory of Environmental Engineering, Shaanxi Province, School of Environmental & Municipal Engineering, Xi'an University of Architecture and Technology, Yan Ta Road. No.13, Xi'an, 710055, China.
Abstract:
Functionalized multiwalled carbon nanotube (f-MWCNT) mixed matrix forward osmosis (FO) membranes were fabricated by phase inversion, and the mechanism of sodium alginate (SA) membrane fouling in the presence of various inorganic components with high ionic strength was thoroughly investigated. The membrane incorporated with 0.5% f-MWCNTs (M-0.5) exhibited enhanced performance, which was attributed to the hydrophilicity of the modified nanoparticles and their good compatibility with the cellulose acetate (CA) substrate. Moreover, it was found that the initial permeate flux decline rate for all FO membranes investigated followed the order Na+ + Ca2+ + Mg2+ > Na+ + Ca2+ > Na+ + Mg2+ > Na+, which was attributed to the particle size of SA macromolecules in the corresponding solutions. However, the gradual change in attenuation was consistent with adhesion force observations made for the SA-fouled FO membrane in the later steady-state stage, and there was little difference among M-0 (without f-MWCNTs), M-0.5, and M-1 (with 1% f-MWCNTs). Furthermore, the SA adsorption layer was most compact in the presence of Ca2+, and the flux recovery rate (FRR) was the lowest after simple hydraulic cleaning, but the overall FRRs for FO membranes were greater than 85%. This implies that although a decrease in electrostatic repulsion leads to the formation of a compact fouling layer, an increase in hydration repulsion of hydrated salt ions plays a major role in membrane fouling under high ionic strength conditions.
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