| dc.description.abstract | Growing water scarcity and rising environmental awareness have posed stricter regulations on industrial wastewater disposal. Since many types of industrial wastewater contains significant amount of salts, desalination is a necessity for responsible wastewater disposal. Membrane distillation (MD) is an emerging thermal desalination technology using a microporous hydrophobic membrane. Compared to reverse osmosis, the state-in-the-art desalination technology, MD has several advantages including the capability of utilizing low-grade waste heat, availability for treating hypersaline brines, low capital cost, and small footprint. However, the adoption of MD in industry is still limited mainly due to certain constraints with conventional hydrophobic membranes, in particular membrane fouling and wetting. Membrane fouling refers to the blockage of membrane pores by hydrophobic contaminants that are rich in certain industrial wastewater. Membrane wetting refers to the penetration of membrane pores by salty solution, which undermines salt rejection. Membrane wetting usually occurs in the presence of low-surface-tension water-miscible liquids (e.g. alcohols) or amphiphilic molecules (e.g. surfactants) in feed waters.
In this dissertation, we elucidated the mechanisms of membrane fouling and wetting, and provided corresponding mitigation strategies. For membrane fouling, we studied the impacts of surface wetting property and surface charge on the fouling resistance of the MD membranes, and thereby provided guidance for the construction of fouling-resistance membranes. For membrane wetting, we firstly developed a novel impedance-based method for monitoring dynamic pore wetting. With this impedance-based method, we compared membrane pore wetting induced by different wetting agents of different nature and elucidated the different wetting mechanisms. Furthermore, we developed a mathematical model to predict the breakthrough time of pore wetting induced by surfactants, which can correctly predict the effects of operating conditions and surfactant species. Finally, with the fundamental understandings of fouling and wetting, we analyzed the strategies for sustaining robust MD operations with different types of feed waters using MD membranes with different wettability. | |
