Janus membrane with simultaneously robust scaling, wetting and fouling resistance for hypersaline organic wastewater treatment via membrane distillation

Membrane distillation (MD) is a promising technology for hypersaline wastewater treatment. However, commercial hydrophobic MD membrane usually suffers from severe wetting/fouling/scaling challenges that seriously hinder its wide applications. It is urgent to develop a robust MD membrane with simultaneous wetting/fouling/scaling resistance in a facile way. In this study, a Janus membrane with a dense hydrophilic nanofiltration top layer was simply fabricated by co-deposition of pyrogallic and polyethylenimine on hydrophobic polyvinylidene difluoride membrane followed by glutaraldehyde cross-linking. The Janus membrane can maintain stable performance during long-term treatment of saline wastewater containing surfactants, oil, and/or mineral ions, suggesting its excellent simultaneous wetting/fouling/scaling resistance. The mechanisms analyses reveal that the excellent wetting/fouling resistance is owed to the combined effects of strong surface hydration barrier, size exclusion, and strong capillary force. Moreover, the positively charged amino groups on the membrane surface further enhance the scaling resistance. Remarkably, the Janus membrane demonstrated exceptional performance during long-term (>100 h) treatment of ethylene waste lye, a hypersaline organic wastewater containing a broad spectrum of contaminants. The membrane possessed stable vapor flux and exhibited near-perfect salt rejection (99 %) and organic rejection (98 %). Our study provides a simple method for designing a robust Janus membrane for treating hypersaline organic wastewater and demonstrates the significant industrial application potential of MD technology.