Effect of operation parameters on the mass transfer and fouling in submerged vacuum membrane distillation crystallization (VMDC) for inland brine water treatment

Abstract

Membrane distillation-crystallization process has great potential to recover high quality water and valuable precipitates from inland brine water. Incorporation of submerging membrane in a feed tank with agitation provides opportunity to reduce temperature and concentration polarization and energy consumption. This study evaluated membrane transverse vibration and feed aeration on the mass transfer of water vapor, crystallization and fouling in a submerged vacuum membrane distillation and crystallization for inland brine water. At selected vibration frequency, more than 700h of high desalination performance was achieved. However, at elevated initial feed conductivity, the operation time was significantly reduced due to severe fouling.With accelerated tests with extreme feed concentration, both transverse vibration and aeration were able to increase the initial flux by reducing boundary layer thickness on the membrane surface. However, with transverse vibration, rapid reduction of flux occurred earlier due to the enhanced CaCO3precipitation on the membrane surface. The aeration of feed improved productivity with longer period of high flux with the increased nucleation in the bulk feed solution. Thermal water softening procedure prolonged the operation time by increased calcium precipitation in the feed solution and slower CaCO3 nucleation on the membrane surface.