Improving the performance of vacuum membrane distillation using a 3D-printed helical baffle and a superhydrophobic nanocomposite membrane

Abstract

Membrane distillation represents a promising solution for high salinity water desalination (e.g. shale gas produced waste wastewater), but so far it has achieved limited commercial success relative to other thermally driven desalination technologies. This study aims to advance membrane distillation technology by systematically investigating three innovative features which can potentially help improve overall performance: a 3D-printed helical baffle, a superhydrophobic membrane coating, and an intermittent operation mode. Our experimental and numerical results reveal that the 3D-printed helical baffle can enhance the permeate flux by 6–46% (depending on flow rate) and increase the average membrane shear by ~60%, with negligible additional pumping power. The impact of a super-hydrophobic coated membrane was evaluated for a synthetic wastewater (35 g/L of NaCl and 0.1 mM of sodium dodecyl sulfate) which mimicked low surface tension shale gas wastewater. It was found that the modified membrane’s flux and salt rejection were maintained ~25% longer than a conventional uncoated polypropylene (PP). Lastly it was found intermittent operation consisting of 5 h of operation followed by 1 h of regeneration doubled module durability compared to continuous operation for the equivalent volume of permeate production. Based on these results, it was estimated that the synergy between these three enhancements would provide >6% more permeate flux and >100% durability, as compared to the baseline. Thus, these results demonstrate that by improving heat and mass transport while also enhancing the hydrophobicity of underlying membranes, it may be possible to make MD systems a viable option for industrial wastewater treatment.