Membrane distillation uses hydrophobic membranes to separate pure distillate water from warm water. Water vapour is transported through the membrane due to a pressure difference caused by the difference in temperature. Because the MD module houses a range of evaporation stages as part of an almost ideal counter-current flow process, a very high recovery of evaporation heat is possible.
Because the process uses hydrophobic membranes, only water vapour can pass through the membrane.
The temperature difference on the two sides of the membrane causes water vapour to diffuse from the hot side of the membrane to the colder side of the membrane. This process of evaporation and condensation cools the hot side and heats the colder side. Using counter-current flows minimizes energy consumption. The process works at low pressures (as low as 1.0 bar).