SolarSpring Publications: Air gap membrane distillation for hypersaline brine concentration

Operational analysis of a full-scale module – New strategies for wetting mitigation


Membrane distillation (MD) is a thermal separation process which possesses a hydrophobic, microporous membrane as vapor space. A high potential application for MD is the concentration of hypersaline brines, such as e.g. reverse osmosis retentateor other saline effluents to be concentrated to a near saturation level with a Zero Liquid Discharge process chain.

In order to further commercialize MD for these target applications, adapted MD module designs are required along with strategies for the mitigation of membrane wetting phenomena. This work presents the experimental results of pilot operation with an adapted Air Gap Membrane Distillation (AGMD) module for hypersaline brine concentration within a range of 0–240 g NaCl /kg solution. Key performance indicators such as flux, GOR and thermal efficiency are analyzed. A new strategy for wetting mitigation by active draining of the air gap channel by low pressure air blowing is tested and analyzed. Only small reductions in flux and GOR of 1.2% and 4.1% respectively, are caused by air sparging into the air gap channel. Wetting phenomena are significantly reduced by avoiding stagnant distillate in the air gap making the air blower a seemingly worth- while additional system component.


  • A novel prototype air gap membrane distillation module is presented
  • Experimental results from module characterization with feed concentrations from 0 to 220 gNaCl/kg solution are shown and discussed
  • Membrane wetting is investigated from a practical and operational perspective
  • Active draining of the air gap channel with an air blower shows good results on maintaining low distillate conductivity at high brine concentrations