Date of Graduation

12-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Chemical Engineering

Advisor/Mentor

Ranil Wickramasinghe

Committee Member

Xianghong Qian

Second Committee Member

Yung Chang

Third Committee Member

Ed Clausen

Fourth Committee Member

Wen Zhang

Keywords

material science, membrane separation, membrane performance

Abstract

Tackling the worldwide severe water shortage, the membrane technology is considered to be the most efficient approach and hence, used widely as a cost-effective sustainable solution. “Forward osmosis (FO)” has been the major attention in recent time. FO uses osmotic pressure as the driving force to draw the water passing the membrane and achieve the desired separation performance. In general, it is considered to be a process with tremendous potential to resolve the present-day water shortage with extremely low energy consumption. However, the challenges of membrane and draw solution regeneration associated with FO processes must be conquered prior to their large-scale application.

In this study, we demonstrated several approaches to enhance the antifouling and FO performance by improving the constituent material as well as developed a novel thermo-responsive process with economic regeneration of the draw solution. The surface charge and fouling adsorption mechanism have been tuned by introducing Polyethylenimine (PEI) on the membrane. Zwitterionic monomer, AEPPS was used to introduce the polyamide layer by conventional in-situ modification and second interfacial polymerization (SIP), respectively. The excellent antifouling surface was verified using a series of fouling test with charged protein adsorption, bacterial adhesion, model secondary wastewater effluents, and hydraulic fracturing produce water.

Beyond the surface decoration, the ultra-thin graphene oxide (GO) FO membrane was fabricated by pressure-assisted self-assembly (PASA). The nanostructure alteration inside the GO layer and crosslinking mechanism was investigated, which could provide a significant advancement to GO material development in the future. Also, we proposed a novel thermo responsive draw solution, which is synthesized from natural and non-toxic material, chitosan. Along with the temperature control, the free volume of the draw solute showed a stable and repeatable change in confirmation. This draw solution has very good prospect to be employed in bio or food-related separation application.

This work is an overall FO process research, which not only enhanced the FO performance and antifouling properties but investigated the material science in detail. Although FO processes are developing and several obstacles are yet to be resolved in terms of large-scale applications, the prospect of commercialization of FO for niche application is expected.

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