Advanced Functionalized Electrospun Membrane for Water Treatment: Comparing Low Frequency Ultrasound Effects on ENMs and PES Membranes in CNC Filtration

Sammanfattning

This thesis investigates how low-frequency ultrasound can enhance membrane filtration performance and reduce fouling, one of the most critical limitations of membranes in water treatment technologies. Two types of membranes were studied. Flat-sheet polyethersulfone (PES) membranes, widely used for their mechanical and chemical stability, and electrospun nanofiber membranes (ENMs) made from styrene-butadiene rubber (SBR), which offer high porosity and permeability. Experiments were conducted in both dead-end and crossflow filtration setups using cellulose nanocrystals (CNCs) as a model foulant. While PES membranes provided stable performance under various conditions, ENMs showed higher initial flux but were more sensitive to fouling and structural degradation, especially in unsupported or thin configurations. Applying ultrasound improved filtration performance in both systems by increasing water flux and partially mitigating fouling, particularly during active ultrasound phases. Notably, this study is among the first to systematically explore the direct application of ultrasound to electrospun membranes during active filtration, an area that had previously remained largely unexamined, despite its promising potential for enhancing membrane performance. To understand the structural dynamics behind fouling, Small-Angle X-ray Scattering (SAXS) was used to analyze how CNCs build up on the membrane over time. This analysis revealed concentration gradients and particle accumulation near the membrane surface, offering valuable insight into the stages of fouling.