Micro-nanobubbles assisted fouling reduction in membrane distillation for desalination

The present study describes the use of micro-nanobubbles (MNBs) as an easy-to-use method for delaying scaling in membrane distillation (MD) while treating highly concentrated saline feed (10 wt.%). The hydrodynamic flow conditions with MNBs are enhanced compared to the traditional gas bubbling in MD. Specifically, an air cushion is formed between the membrane surface and bulk, limiting the deposition of solid particles on the surface. Also, turbulence created by the MNBs reduces the membrane fouling. The findings of the MD performance analysis showed that, in the absence of nanobubbles, considerable membrane scaling occurred during the treatment of high-salinity feed, which significantly decreased the distillate flux to 70% after 20 h. The one-time incorporation of air NBs into the saline feed significantly reduced salt precipitation or fouling on the polyvinylidene fluoride (PVDF) membrane surface by delaying the start of flux drop and preventing membrane wetting, thus improving MD performance. For nanobubble-assisted MD, the only measured flux drop after 20 h of operation was 57% under similar input concentration and operating parameters.