Abstract
Membrane distillation (MD) is a novel desalination technology that has potential to produce distilled quality water from high salinity brine streams. The driving force for MD is the vapor pressure difference across a hydrophobic membrane resulting in transfer of water vapor from hot to cold side. This vapor contacts a cold surface and condenses to produce distillate. This paper reviews recent and/or multi-year research programs that focused on MD pilot or field testing. The various investigations concluded that while MD can produce distilled water quality, the energy efficiency remains the key bottleneck for future deployment of MD. Membrane wetting and fouling also presents key challenges for desalination due to both the high salinity and the presence of organics in the feed water. The authors contacted several MD vendors requesting updates on their latest products and technology developments. MD vendors with innovative module designs, some of which promise a step change in performance, have recently emerged on the market. In addition to water desalination, MD has a wide range of industrial applications such as hydrogen sulfide removal, the treatment of wastewater from the pharmaceutical, metal finishing industries, direct sewer mining, oily wastewater, and water recovery from flue gas. This paper also reviews novel membrane chemistries with emphasis on membranes prepared by phase inversion and electrospinning techniques to which nanomaterials have been added. The primary objectives in adding various nanomaterials (e.g., carbon nanotubes, graphene, silicon dioxide, fluorinated compounds) are to increase hydrophobicity (to reduce wetting) and increase mass transfer rates (to increase flux and lower cost).
Highlights
Membrane distillation (MD) is a hybrid thermal-membrane process driven by the vapor pressure difference between hot and cold sides of a hydrophobic membrane, resulting in the passage of water vapor through the membrane, followed by condensation on the cold side producing distilled quality water [1, 2]
The target application of MD is the desalination of saline waters such as seawater or brines
MD is a hybrid thermal-membrane process driven by the vapor pressure differential across the hot and cold sides of a hydrophobic membrane resulting in passage of water vapor through the membrane, followed by condensation to produce distilled water
Summary
Membrane distillation (MD) is a hybrid thermal-membrane process driven by the vapor pressure difference between hot and cold sides of a hydrophobic membrane, resulting in the passage of water vapor through the membrane, followed by condensation on the cold side producing distilled quality water [1, 2]. The other niche applications of MD and hydrophobic membranes are fruit juice concentration in the food industry [13], treatment of wastewater from electronic industry [14], metal finishing and pharmaceutical industries [15], and removal of specific gas streams such as hydrogen sulfide from process water [16]. These industries focus more on recovering the value-added products or removal of key contaminants which can justify the energy consumption. The modified membranes have shown superior performance for the treatment of high saline water containing oil, surfactant, and stabilized emulsion [20]
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