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Elektrisch angesteuerte Gold-Polymer-Gold-Ultrafiltrationsmembranen zur Aufbereitung NOM-haltiger Wässer
Citation Link: https://doi.org/10.15480/882.4287
Publikationstyp
Doctoral Thesis
Publikationsdatum
2022-04-08
Sprache
German
Author
Mantel, Tomi Jonathan
Advisor
Referee
Title Granting Institution
TU Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2022-02-23
Citation
Technische Universität Hamburg (2022)
Humanity is facing a water crisis due growing water demand of an increasing population, economic development, water pollution, and climate change. Ultrafiltration (UF) is a promising technology for countering the global water crisis due to its high removal potential for pathogens and turbidity at high recovery and low demand of chemicals. However, it suffers from membrane fouling and low removal performance for organic water constitutes such as natural organic matter (NOM). The selectivity for NOM increases when the pore size of the UF membrane is decreased but this also leads to reduction of permeability and energy efficiency. This problem is called the selectivity-permeability trade-off. Electrically conductive UF membranes are a new approach which might offer a solution to these problems. Most NOM are negatively charged. By application of a negative or positive electrical potential to the membrane surface, a repulsive or attractive force is induced on the charged substances in the feed water, respectively, which influences the rejection and fouling behavior of these membranes.
In this work, an ultra-thin gold coating was applied on the active and support layer of flat-sheet polymer membranes to achieve electrical conductivity. Due to the coating of both sides of the membrane, no additional counter electrode was necessary to apply an external potential. An intrinsically negatively charged polyethersulfone (PES, UP150) and an intrinsically positively charged polyamide (M5) membrane were used for electro-repulsive and electro-sorptive filtration experiments, respectively.
In the first part of this thesis, the membranes were characterized before and after the gold-coating regarding its filtration and electrochemical properties. Sputter coating only slightly changed the filtration properties of the membranes. The molecular weight cut-off was almost not affected by the gold coating. However, the pure-water permeability was reduced by 15 % and 40 % for the M5 and UP150 membrane, respectively.
In the second part of this thesis, electro-repulsive filtration was conducted with model NOM solutions and natural lake water with the UP150 membrane. At filtration of Hohloh lake water the permeability decreased by 49 % (± 2 %) when no external potential was applied (0 V). However, when negative potential was applied the permeability only decreased by 17 % (± 3 %) (at -2.5 V). The application of negative potential to the membrane active layer led to less fouling and an increased NOM rejection at cross-flow mode. The molecular weight cut-off was shifted from 150 kDa at no applied potential to 5 kDa at -2.5 V (cell potential). Therefore, it could be seen that the duplex-coated membrane configuration was almost as effective as conventional counter electrode configuration in fouling mitigating and rejection enhancement.
In the third part, electro-sorptive dead-end filtration experiments showed that the application of a positive potential led to adsorption of NOM and negatively charged organic dye molecules. When the potential was reversed to negative potential, the previously adsorbed substances could be desorbed. The process of electrosorptive UF worked with the intrinsically positively charged M5 membrane but not with the intrinsically negatively charged UP150. The molecular weight cut-off of the M5 membrane was shifted from approx. 1000 kDa at no applied potential to approx. 0.7 kDa at +2.5 V (cell potential). Therefore, the electrosorptive UF achieved a NOM rejection performance in the range of commercially available nanofiltration membranes. At the same time, the positively charged M5 membrane showed permeability in the range of loose UF membranes and fouling was not observed to be problematic. The additional energy consumption for the application of the external potential was low with 0.03 kWh/m³ of permeate.
Overall, electro-repulsive and electro-sorptive UF membranes, both, broke the selectivity-permeability trade-off of the UF process. Whereas, the electrosorptive enhancement of NOM removal was more pronounced than the electro-repulsive.
In this work, an ultra-thin gold coating was applied on the active and support layer of flat-sheet polymer membranes to achieve electrical conductivity. Due to the coating of both sides of the membrane, no additional counter electrode was necessary to apply an external potential. An intrinsically negatively charged polyethersulfone (PES, UP150) and an intrinsically positively charged polyamide (M5) membrane were used for electro-repulsive and electro-sorptive filtration experiments, respectively.
In the first part of this thesis, the membranes were characterized before and after the gold-coating regarding its filtration and electrochemical properties. Sputter coating only slightly changed the filtration properties of the membranes. The molecular weight cut-off was almost not affected by the gold coating. However, the pure-water permeability was reduced by 15 % and 40 % for the M5 and UP150 membrane, respectively.
In the second part of this thesis, electro-repulsive filtration was conducted with model NOM solutions and natural lake water with the UP150 membrane. At filtration of Hohloh lake water the permeability decreased by 49 % (± 2 %) when no external potential was applied (0 V). However, when negative potential was applied the permeability only decreased by 17 % (± 3 %) (at -2.5 V). The application of negative potential to the membrane active layer led to less fouling and an increased NOM rejection at cross-flow mode. The molecular weight cut-off was shifted from 150 kDa at no applied potential to 5 kDa at -2.5 V (cell potential). Therefore, it could be seen that the duplex-coated membrane configuration was almost as effective as conventional counter electrode configuration in fouling mitigating and rejection enhancement.
In the third part, electro-sorptive dead-end filtration experiments showed that the application of a positive potential led to adsorption of NOM and negatively charged organic dye molecules. When the potential was reversed to negative potential, the previously adsorbed substances could be desorbed. The process of electrosorptive UF worked with the intrinsically positively charged M5 membrane but not with the intrinsically negatively charged UP150. The molecular weight cut-off of the M5 membrane was shifted from approx. 1000 kDa at no applied potential to approx. 0.7 kDa at +2.5 V (cell potential). Therefore, the electrosorptive UF achieved a NOM rejection performance in the range of commercially available nanofiltration membranes. At the same time, the positively charged M5 membrane showed permeability in the range of loose UF membranes and fouling was not observed to be problematic. The additional energy consumption for the application of the external potential was low with 0.03 kWh/m³ of permeate.
Overall, electro-repulsive and electro-sorptive UF membranes, both, broke the selectivity-permeability trade-off of the UF process. Whereas, the electrosorptive enhancement of NOM removal was more pronounced than the electro-repulsive.
Schlagworte
NOM, Ultrafiltration, Elektrisch leitfähige Membranen
DDC Class
620: Ingenieurwissenschaften
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