Optical method for in operando study of membrane distillation wetting: Development for desalination and potential for exploring wetting dynamics

International audienceA proof of concept of an optical method for the in operando detection of wetting in membrane distillation has previously been established in the case of fast and total wetting provoked by surfactants. The present study adapts this concept to develop a method enabling the in operando detection and quantification of wetting in desalination. The most unfavorable conditions for wetting were chosen: saline solutions not prone to scaling, which are often also considered to not be prone to wetting. Even for these solutions, variations in the light in-tensity can be detected and wetting optical indicators can be defined for both local-and global-scale analyses of the membrane area. A wetting cartography, showing and quantifying the occurrence of water intrusion in pores at the local scale can be established for each operating time. Comparison of these cartographies at different times enables the wetting front and its displacement to be visualized. This method can also be used to further study the influence of operating conditions on wetting and its dynamics. As examples, the influence of feed salinity and a comparison of two membranes of different average pore size on the wetting cartography and dynamics are presented here