Development of a dual-layered PVDF-HFP/cellulose membrane with dual wettability for desalination of oily wastewater

Meeting environmental discharge or reuse water qualities and freshwater demands requires the development of innovative processes like membrane distillation (MD) for treating oily wastewater. Desalinating oily wastewater through MD is, however, challenging because of immediate contamination and wetting of the membrane caused by oil or other low surface tension contaminants. In this work, a novel concept of stacking two membranes with different wettabilities to obtain a dual-layered membrane was developed. The hydrophilic top layer, composed of electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and regenerated cellulose, displayed superoleophobicity underwater and prevented oil passage to the hydrophobic PVDF-HFP bottom layer during MD process. When tested in direct contact MD of saline feed containing 1000 ppm of oil, the stacked dual-layered membrane yielded fresh water flux up to 12.8 kg m⁻² h⁻¹ with complete salt rejection.