Preparation of a fouling-resistant Teflon/PVDF composite membrane and its application to treat nanofiltration brine from landfill leachates

Landfill leachates (LFLs) pose a severe environmental threat given their high strength and the slow degradation nature of their organic and inorganic pollutants constituents. Hence, they are challenging to treat by conventional wastewater treatment methods. Although membrane distillation (MD) is promising for wastewater treatment, membrane wetting and scaling that lead to membrane fouling are the bottlenecks in applying this technology to LFLs. In this work, a commercial Teflon emulsion was used to modify the PVDF membrane via a simple dip-coating method, followed by depositing the PTFE particles onto the membrane surface via thermal curing crosslinking reaction. Hence, a Teflon/PVDF composite membrane was successfully prepared with resistance to sodium dodecyl sulfate wetting, CaSO4 scaling, and humic acid fouling. Effects of the Teflon emulsion concentration and dipping time on the composite membrane's chemical composition, surface characteristics, porosity, mechanical properties, liquid entry pressure (LEPW), and direct contact membrane distillation (DCMD) performance were systematically investigated. The results showed that Teflon emulsion modification could improve the membrane surface's hydrophobicity, reduce pore size, and increase mechanical strength. The Teflon/PVDF composite membrane with 100% Teflon emulsion and 10 min dipping time exhibited the highest hydrophobicity and 144.3º water contact angle. The M100-10 membrane also exhibited stable performance for treating nanofiltration (NF) brine collected from the LFL. When concentrating the NF brine, the M100-10 membrane achieved only a 7.1% flux decay rate. Hence, the Teflon/PVDF composite membrane demonstrated excellent wetting, scaling, and fouling resistance. This dip-coating method is simple, low cost, easy to scale up, and has potential in the large-scale production of hydrophobic porous membranes.