How to select a membrane distillation configuration? Process conditions and membrane influence unraveled

In membrane distillation, the liquid phase including dissolved components is retained by a hydrophobic membrane, while the microporous structure allows transport of vapor through the membrane. The vapor pressure difference over the membrane is the driving force and is applied using a variety of configurations. This paper directly compares the flux and energy efficiency of a lab scale direct contact membrane distillation (DCMD), air gap membrane distillation (AGMD), permeate gap membrane distillation (PGMD) and vacuum membrane distillation (VMD) using the same bulk driving force. The highest flux was observed for VMD, followed by DCMD > PGMD > AGMD. Furthermore, it was observed that the different configurations are not equally sensitive to the applied process conditions, including temperature difference, flow velocity and salinity. For the first time, also the importance of the specific requirements for the membrane for each configuration was investigated.