Abstract
High water flux and elevated rejection of salts and contaminants are two primary goals for membrane distillation (MD). It is imperative to study the factors affecting water flux and solute transport in MD, the fundamental mechanisms, and practical applications to improve system performance. In this review, we analyzed in-depth the effects of membrane characteristics (e.g., membrane pore size and distribution, porosity, tortuosity, membrane thickness, hydrophobicity, and liquid entry pressure), feed solution composition (e.g., salts, non-volatile and volatile organics, surfactants such as non-ionic and ionic types, trace organic compounds, natural organic matter, and viscosity), and operating conditions (e.g., temperature, flow velocity, and membrane degradation during long-term operation). Intrinsic interactions between the feed solution and the membrane due to hydrophobic interaction and/or electro-interaction (electro-repulsion and adsorption on membrane surface) were also discussed. The interplay among the factors was developed to qualitatively predict water flux and salt rejection considering feed solution, membrane properties, and operating conditions. This review provides a structured understanding of the intrinsic mechanisms of the factors affecting mass transport, heat transfer, and salt rejection in MD and the intra-relationship between these factors from a systematic perspective.
Highlights
Freshwater scarcity is a grand challenge that threatens water security and economic development.Desalination and water reuse provides a viable solution to improving water security and alleviating water stress by expanding alternative water supplies, such as seawater, brackish water, wastewater, and other impaired water sources [1,2,3]
This review focuses on analysis and deliberations of membranes, feedwater chemistry, operating conditions and their interactions on membrane distillation (MD) performance in terms of their impacts on flux and salt rejection (SR)
Eykens et al [156] observed a very similar result using a commercial polyvinylidene fluoride (PVDF), PP membranes, and a lab-scale made e-PVDF membrane. They suggested broader optimum membrane thickness ranges of 2–30 μm for 3 wt.% NaCl feed solution, 7–112 μm for 13 wt.% NaCl feed solution, and 16–793 μm for 24 wt.% NaCl feed solution. Their results revealed that a higher hydrophobic layer thickness was more suitable for MD application when fed with a high salinity solution
Summary
Freshwater scarcity is a grand challenge that threatens water security and economic development. MD can take advantage of solar [28,29,30,31], heavy metal removal [32], separation of organic solutes [33,34], treatment of covers water energy, geothermal energy, and waste heat of industries to sustain the driving force. These review papers have covered ceramic membranes applied for MD [84], and perspective on sustainable and renewable desalination broad research energy efficiency analysis, membrane development, of using MD [68,85].areas. Theseincluding review papers have covered broad research areas including energyeffects efficiency membrane properties and MD module configurations on MD performance, fouling and scaling analysis, membrane development, effects of membrane properties and MD module configurations on control in MD, modeling heat transfer, and mass transfer in MD. MD performance, fouling and scaling control in MD, modeling heat transfer, and mass transfer in MD
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