Advancing Hollow Fiber Nanofiltration Membranes: Materials, Structure, and Performance

Many regions of the world are dealing with an increasing scarcity of fresh water. This increase in scarcity is caused by climate change, a growing population, and increased industrialization, resulting in more droughts, higher demand, and more contaminants in our supplies. One method of combating this water scarcity would be to increase the amount of wastewater reuse. To enable such re-use, adequate and affordable wastewater treatment facilities will need to be installed, which are preferably fabricated using sustainable materials. One of the technologies that can be used for the treatment of wastewaters is polyelectrolyte multilayer (PEM) nanofiltration membranes. However, the current method of fabrication of PEMs leaves room for improvement with regard to the active membrane surface area that can be packed into a single membrane module, the permeability of the hollow fiber (HF) PEM membranes, and the sustainability of the coated PEM. Therefore, in this work, we investigated methods of improving these aspects of PEM membranes to develop the next generation of affordable and sustainable HF PEM nanofiltration membranes for wastewater reuse.
The outline of this thesis is as follows: Chapter 1 motivates the work and provides an overview of the fundamentals of HF PEM NF membranes. Chapter 2 investigates increasing the active membrane surface area that can fit into a membrane module by inverting the porous structure of the support membrane to produce an outer-skinned PEM membrane. The concept of outer-skinned PEM membranes is further investigated in Chapter 3 by looking into how the collapse pressure of these membranes can be predicted and improved. Chapter 4 focuses on reducing the operational costs of an HF PEM membranes by focusing on increasing its permeability. To this end, soluble nanoparticles are investigated as sacrificial pore fillers to decrease the thickness of the final PEM. Chapter 5 looks into the use of lignin as a biobased and biodegradable alternative polyelectrolyte for the fabrication of more sustainable PEMs. Finally, in Chapter 6, an overview of the main conclusions of the work is provided together with an outlook.