Mitigation of organic fouling in membrane distillation via 3D printed wavy composite membranes

Membrane distillation (MD) has the potential to tackle water scarcity challenges, as it can process non-traditional water sources to meet the growing water demand globally. However, long-term operation of MD systems is hampered by fouling of the membrane's surface which leads to reduced process efficiency. To address this, this study utilised 3D printed double sinusoidal (wavy) supports designed to enhance hydrodynamics at the membrane surface, mitigate organic fouling, and improve cleaning efficiency in air gap MD (AGMD). Computational Fluid Dynamics (CFD) simulations of turbulent water flow showed that wavy surfaces enhance surface shear stress and turbulent kinetic energy, reducing foulant deposition and facilitating foulant detachment during cleaning. Polyvinylidene fluoride (PVDF) hydrophobic films (thickness > 100 μm) were attached to 3D printed flat and wavy supports via vacuum filtration, and their long-term AGMD performance was assessed. The composite membranes were tested continuously over 12 days using saline solutions containing humic acid, with a cleaning cycle every 3.5 days. A wavy membrane with a mixed matrix PVDF selective layer containing clay as a filler material, showed best-in-class performance, with a flux decrease of only 28 % and a flux recovery of 91 % before and after the third cleaning cycle, respectively. For comparison, a commercial PVDF membrane and an in-house fabricated pristine PVDF membrane without any support, showed a flux decrease of 43 and 48 % and flux recovery of 65 and 60 %, respectively, confirming the CFD observations on the anti-fouling behaviour of wavy membranes. Overall, 3D printing allowed the fabrication of novel MD membranes with anti-fouling properties for long-term, efficient desalination and water treatment.