Water Recovery from Highly Saline Dye Wastewater by Membrane Distillation Using a Superhydrophobic SiO₂/PVDF Membrane

Membrane distillation (MD) has been widely used for resource recovery from high-salinity wastewater, due to its superior technical merits of high separation efficiency and potential integration of low-grade heat. Herein, a robust superhydrophobic PVDF membrane prepared by spray-coating of fluorinated silica nanoparticles was employed to treat highly saline dye wastewater by MD. Specifically, impacts of operation conditions, including temperature difference, feed flow-rate, salinity, dye concentration, and dye species, on MD performance of the fabricated superhydrophobic PVDF membrane were comprehensively investigated. The increase of temperature difference and feed flow-rate had a positive effect on the MD flux of the membrane. Conversely, the rise in salinity and dye concentration induced an adverse impact on the MD flux. Furthermore, the superhydrophobic PVDF membrane showed a strong robustness in treating complex streams, as demonstrated by consistently stable MD flux using various dye/NaCl mixed solutions. Due to the robust surface superhydrophobicity, the fabricated PVDF membrane exhibited impressive antiwetting and antifouling properties against highly saline dye wastewater, consistently stable permeation flux, and high dye/salt removal efficiency (>99.99%). Moreover, the superhydrophobic membrane showed a high water recovery (90%) from highly saline dye wastewater with a slight reduction (13.4%) in permeation flux during a 39 h MD filtration. These results signify the promising practicability of the fabricated superhydrophobic PVDF membrane in sustainable management of highly saline dye wastewater via MD.