Wetting, Scaling, and Fouling in Membrane Distillation: State-of-the-Art Insights on Fundamental Mechanisms and Mitigation Strategies

Abstract

Membrane distillation (MD) has been garnering increasing attention in research and development, since it has been proposed as a promising technology for desalinating hypersaline brine from various industries using low-grade thermal energy. However, depending on the application context, MD faces several important technical challenges that would lead to compromised performance or even process failure. These challenges include pore wetting, mineral scaling, and membrane fouling. This review is devoted to providing a state-of-the-art understanding of fundamental mechanisms and mitigation strategies regarding these three challenges. Guided by the fundamental understanding of each membrane failure mechanism, we discuss both operational and material strategies that can potentially address the three technical challenges. In particular, the material strategies involve the development of MD membranes with tailored special wetting properties to impart resistance against different types of membrane failure. Lastly, we also discuss research needs and best practices in future studies to further enhance our ability to overcome technical challenges toward the practical, sustainable, and scalable applications of MD.

Highly Salt‐Resistant 3D Hydrogel Evaporator for Continuous Solar Desalination via Localized Crystallization

“…Moreover, systemic heat loss by heating up of surrounding air is related to the exposed surface area, which directly results in a decreasing temperature gradient in the radial direction. The simultaneously formed interfacial tension [ 40 ] and salt nucleation [ 41 ] difference also lead to the edge‐preferential salt crystallization, maintaining sustainable running during high‐salinity brine desalination.…”

Janus membranes for membrane distillation: Recent advances and challenges

“…In the case of hydrophobic membrane, due to the strong hydrophobic-hydrophobic interaction, oil wicks through the membrane, clogs the pores and causes fouling of the membrane [29]. For omniphobic membrane, the membrane surface is also covered by the oil particles due to hydrophobic interaction and foul the membrane, however the oil particles do not wick into the pores and the fouling is reversible via commonly used cleaning methods like backwashing [11]. Janus membranes have thin hydrophilic layer that are hydrated with water, showing underwater oleophobicity, which can repel oil droplets and avoid oil fouling formation.…”

“…Although different studies generally attributed the wetting mechanism to the change in hydrophilicity of membrane pores by adsorption of the surfactants on the pore walls (Figure 1) [8], recent studies focusing on the wetting mechanism proved that the main reason for pore wetting is the reduction of surface tension of the feed stream [9]. These studies also proved that adsorption of the surfactants on the pore walls can delay the wetting by removing the surfactants from the water-gas frontier [9][10][11].…”

“…This can be obtained by designing a hierarchical structure or re-entrant surface structure followed by coating with a low surface energy layer [27,28]. However, omniphobic membranes are still prone to fouling issues due to hydrophobic foulants like oil droplets [11,29]. Thus, continued efforts are still done to design a membrane that can potentially reduce fouling formation, while resisting wetting and maintaining adequate flux and rejection.…”

National Alliance for Water Innovation (NAWI) Agriculture Sector Technology Roadmap 2021

“…Anti-fouling membranes and surfaces, including those with special wettability and grafted with biocidal materials, have been developed, with the underlying mechanisms of fouling resistance elucidated. 263,264,265,266 However, such materials are typically tested in short-term experiments, and their effectiveness in long-term performance tests is unknown. Compared to extensive studies on organic and biological fouling, similar knowledge on inorganic scaling and the corresponding scaling-resistant membranes has yet to be established.…”