The application of polypropylene membranes for production of fresh water from brines by membrane distillation

Scaling and wettability of hydrophobic membranes were studied during the membrane distillation applied for the production of fresh water from the concentrated salt solutions. The studies were performed with the use of membrane modules in which the capillary membranes from polypropylene were assembled. A saline ground water containing several sparingly soluble salts was used as a feeding solution. The presence of such compounds caused an intensive surface and internal scaling. Due to the scaling, a partial wetting of the membrane walls and the permeation of salts into distillate were observed. These phenomena were eliminated for the membranes with thicker walls when the amount of deposit was limited by a periodic rinsing of the module with water. During this study, the feed was concentrated up to the supersaturation state, which caused a salt crystallization on the membrane surface, and as a consequence, the permeate flux was reduced to zero. In this case, the internal scaling can be limited using the capillary membranes with a net covering their surface.