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Development and performance of Layer-by-Layer modified hollow fiber membranes as capillary nanofiltration
Citation Link: https://doi.org/10.15480/882.15087
Publikationstyp
Doctoral Thesis
Date Issued
2025
Sprache
English
Author(s)
Stumme, Jakob
Advisor
Referee
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2024-09-03
TORE-DOI
First published in
Number in series
10
Citation
Institut für Wasserressourcen und Wasserversorgung 10: (2025)
Peer Reviewed
false
The need for alternative water sources due to water stress or changes in raw water qualities for use as drinking water often requires more advanced treatment techniques than currently in use. Thus, there is a demand for resource and energy efficient processes, with high process stability and reliability. Within this work the potential of Layer-by-Layer (LbL) modified hollow fiber ultrafiltration (UF) membranes was examined as one option in terms of ion rejection, rejection of dissolved organics, molecular weight cut-off (MWCO), fouling, and mechanical and process stability. Furthermore, a model was derived to differentiate between predominant polyelectrolyte (PE) build up during modification in terms of pore vs layer dominating PE multilayer formation. The results also identified the PE layering location as another crucial factor during membrane modification. Filtration in lab scale as well as pilot scale results in water works achieved high rejection rates for divalent ions (> 90 % for sulfate and magnesium, and > 80 % for calcium). However, some external parameters were investigated which influenced the resulting ion rejection. As shown in lab scale, high ionic strength in the feed solutions led to swelling of the PE structure, resulting in a change of separation characteristics. Nevertheless, swelling was highly dependent on the present type of ions and respective concentration. Model supported results clearly identified concentration polarization (CP) through the laminar boundary layer as dominating factor for the removal efficiency for sulfate as a model substance for divalent ions. Besides crossflow velocity and resulting laminar boundary layer thickness, model results showed a severe influence of CP dependent on membrane length. This underscores the importance of additional experiments beyond the lab to pilot scale on industrial length modules. Further investigations in lab scale showed that the modification of the membranes resulted in an MWCO in the lower range of NF membranes, providing high removal rates of dissolved organic substances. SAC254 removal rates of > 90% and TOC removal of > 80 % could be achieved even in Dead End operation for solutions containing natural organic matter (NOM). Fouling and removal rates were dependent on the NOM composition and their molecular weight distribution. Hereby, the solution containing a higher share of larger molecules reached higher rejection, while impact of fouling was lower. It is attributed to the deposition of foulants on top of the membrane surface instead of internally within the modified membrane structure. Membranes could successfully withstand the stress of hydraulic backwash (hydr. BW), though it was limited to a maximum hydr. BW flux of 50 L/(m² h). Combined with the good chemical stability, it would allow the implementation of a regular CEB, which was highly efficient for the removal of NOM foulants off the membrane surface. Overall, the LbL modification of hollow fiber UF membranes was successful on lab scale and on industrial scale membranes and could be operated successfully for several months in two different waterworks. The modified membranes combined exceptionally high NOM removal rates with the possibility for high divalent ion rejection and the stability of regular mechanical and chemical cleaning. Thus, LbL modified hollow fiber UF membranes did show a great potential for treatment of waters with high contents of dissolved organics and particle loads.
Subjects
LbL
Layer-by-Layer
membrane filtration
drinking water treatment
membrane modification
membrane development
DDC Class
541: Physical; Theoretical
620.1: Engineering Mechanics and Materials Science
628.1: Water Supply Systems
660: Chemistry; Chemical Engineering
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Stumme_Jakob_2025_Development_and_performance_of_Layer-by-Layer_modified_hollow_fiber_membranes_as_capillary_nanofiltration.pdf
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Adobe PDF
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