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. 2019 Dec 20;12(1):23. doi: 10.3390/polym12010023

Table 5.

Factors affecting membrane wetting and fouling in the MD process.

Parameters Factors Comments References
Operational conditions Effect of temperature Salts, such as CaSO4 and CaCO3, which have a negative correlation of solubility with respect to temperature also tend to become saturated in the feed stream of desalination.
Typically, for commonly utilized feed solutions, increased temperature leads to increased risk of scaling and fouling
[69,70]
Effect of dissolved gases The presence of dissolved gases in the feed stream leads to chemical processes, such as the breakdown of bicarbonates which penetrate the membrane pores along with water vapor, exerting an additional diffusive resistance for the water vapor. [52]
Membrane properties Thickness of the membrane Membrane thickness seems to be inversely proportional to the mass and heat transfer rate across the MD membrane. Thus, an optimized membrane thickness must be utilized. [71]
Pore size distribution The pore size of the MD membrane ranges from 0.1 µm to 1 µm
In general, pore size affects the mass transfer mechanism. For instance, one side of the membrane, the pore size should be small so that water or liquid cannot penetrate into the pores, while, the pore size must be large on another side, in order to achieve high permeate flux.
[72]
Porosity Higher porosity of the membrane offers more water flux, but rapidly wets the membrane [73]
Surface energy A low surface energy offers high hydrophobicity [74]
Feed solution chemistry Surface tension If the feed solution is composed of surfactants higher than the critical value, membrane and pore wetting occurs. Thus, feed streams with a low surface tension must be avoided [75]
Concentration of non-volatile solutes A higher concentration of inorganic salts may result in the formation of salt crystals onto the membrane surface, leading to wetting of membrane portions occupied by salt crystals. Therefore, a higher concentration of inorganic salts may lead to the formation of a cake layer of inorganic foulants that leads to membrane and pore wetting [76]
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