Wetting, Scaling, and Fouling in Membrane Distillation: Mitigation Strategies via Development of Advanced Membranes with Special Wettability and Application of Nanobubbles

膜蒸餾的膜潤濕、結垢和污染﹔透過研發先進潤濕特性膜和應用納米氣泡技術的緩解方案

Student thesis: Doctoral Thesis

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Award date27 Aug 2021

Abstract

Accelerated by unprecedented population growth, depletion of water reserves, and climate change, water scarcity has become a serious global concern. Efficient desalination technologies, which can augment the supply of fresh water, are key in addressing this major challenge. To this end, membrane distillation (MD) is an emerging membrane-based thermal technology that has gained substantial interest both in academia (research) and industry (start-ups). Given its distinct advantages, such as tolerance to hypersaline waters, modular design, non-necessity of high pressure, and low operation temperatures, MD applications have been expanded into promising niche areas. Particularly, these applications are useful for the treatment of hypersaline waters, a category that includes gas- and oil-produced waters, brine from water desalination, and brine generated from zero liquid discharge processes, which the state-of-the-art membrane desalination process, reverse osmosis, and thermal distillation technologies fail to achieve. However, the industrial-scale application of MD remains limited due to technical and engineering challenges.

This research aims to better understand and provide solutions for three major challenges in MD: wetting, scaling, and fouling. Studies addressing wetting have focused on chemical surface modifications for the design and fabrication of advanced membranes with special wettability, including superhydrophobic and omniphobic membranes. Superhydrophobic membranes have shown good wetting resistance against saline feeds with moderate or low surface tension containing up to 0.4 mM sodium dodecyl sulfate (SDS), and omniphobic membranes have shown superior wetting resistance against ultralow-surface-tension saline feeds containing high concentrations of both SDS (>1 mM) and oil (>400 ppm). Fouling studies, including those on total fouling caused by the constituents of real seawater and organic fouling caused by oil in simulated industrial wastewater, have focused on physical and chemical surface modifications for the development of patterned and Janus membranes. Patterned membranes have been developed by introducing a simple imprinting step to the fabrication process; when tested with real seawater, they have shown improved fouling resistance due to the induced surface turbulence and favorable flow hydrodynamics. Moreover, patterned membranes have shown enhanced membrane flux due to an increase in the effective membrane surface area. Janus membranes with a thin hydrophilic surface coating layer and an omniphobic substrate have shown robust fouling resistance against feeds having oil concentrations of more than 1000 ppm. Finally, scaling mitigation via a chemical-free strategy, that is, the use of nanobubbles, for the treatment of ultrahigh-salinity brine was investigated. This work is the first to study inorganic fouling mitigation in MD processes via nanosized air bubbles.

    Research areas

  • Membrane distillation, Wetting, Scaling, Fouling, Superhydrophobic, Omniphobic, Janus, Nanobubbles, SiNPs