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Ph.D. Thesis Defense Announcement
OSMOTICALLY DRIVEN MEMBRANE PROCESSES FOR WATER TREATMENT: MEMBRANE SYNTHESIS AND TRANSPORT MECHANISM EXPLORATION
by
Su Liu
Advisor(s):
Dr. John Crittenden
Committee Members:
Dr. Yongsheng Chen (CEE); Dr. Xing Xie (CEE); Dr. Sotira Yiacoumi (CEE); Dr. Marta Hatzell (ME)
Date & Time: Dec. 15 9:00 AM
Location: https://bluejeans.com/949477642
Complete announcement, with abstract, is attached
Osmotically driven membrane processes are promising technologies for water treatment which use osmotic pressure difference as the driving force. Forward osmosis (FO) is a typical osmotic pressure-driven membrane process. The membrane is the key component of an FO membrane system; however, the lack of high-performance membranes hinders the large-scale applications of FO. The overall objective of this research is to design efficient membranes specifically for osmotically driven membrane processes for water treatment and to understanding the underlying transport mechanisms.
Specifically, the FO membrane was modified with an innovative organic coating layer. The modified membrane has a more hydrophilic, less rough surface and reduced pore size. The membrane overall performances, including reverse salt selectivity, anti-fouling property, and rejection of the micropollutants, were enhanced with a mild water permeability loss. Graphene oxide membranes (GOMs) are promising separation technologies because of the high water permeability. In addition, the reverse salt flux (salt flux from the draw solution to the feed solution) is low in FO. However, the rejection is low (forward salt flux is high) in the hydraulic pressure driven mode. This counterintuitive phenomenon was studied to understand the transport mechanisms in GOMs. Based on the analysis in this study, the water flux from the feed solution to the draw solution can retard the ion transport from the draw solution to the feed solution. In addition, the extension of electrical double layer (EDL) thickness also has a screening effect on retarding the reverse ion transport. To further explore the potential applications for GOMs to be used in osmotically driven membrane processes for water treatment, the investigation of forward solute transport was initiated with the freestanding GOMs. The freestanding GOM has a better separation performance for multivalent ions than the monovalent ions. The analysis shows the forward solute transport of the charged solute is mainly governed by the steric exclusion, interfacial Donnan exclusion and EDL screening along the nanochannels in the GOMs. The findings in this study can provide a further guidance for the future membrane design and applications exploration for the osmotic pressure driven membrane processes.
