End-to-end management of membrane distillation for oily wastewater desalination: tailoring polyamide membranes, monitoring fouling dynamics, and implementing cleaning protocols

Membrane distillation (MD) for the treatment of high-salinity, oil-containing wastewater is fundamentally constrained by the coupled challenges of membrane wetting and fouling, while a systematic, end-to-end solution for practical implementation remains elusive. In this work, a defect-minimized and mechanically robust polyamide (PA) thin-film composite membrane (#TFC-3) was fabricated on a hydrophobic #PTFE substrate via successive reverse interfacial polymerization (IP). This sequential design enabled synergistic layer evolution, wherein the initial IP tailored the substrate surface to facilitate subsequent layer formation, while later-stage IP effectively healed defects in the preceding layers, yielding an integrated and highly resilient selective structure. When challenged with feeds containing anionic sodium dodecyl sulfate (SDS), cationic dodecyl trimethyl ammonium bromide (DTAB), or nonionic polyoxyethylene (20) sorbitan monolaurate (Tween-20) surfactants (4 mM), as well as emulsified oil (400 ppm), the optimized #TFC-3 demonstrated substantially enhanced resistance to wetting and fouling compared to the original #PTFE, as evidenced by more stable desalination performance. Additionally, electrochemical impedance spectroscopy (EIS) enabled real-time monitoring and early-stage detection of wetting processes induced by these foulants, offering greater sensitivity than conventional conductivity-based methods. Guided by EIS diagnostics, timely cleaning interventions effectively suppressed wetting progression, maintaining over 75% flux recovery even after 10 cleaning cycles. Furthermore, long-term evaluation (15 days) using real produced water from offshore oil extraction confirmed the operational stability and treatment efficacy of the developed membrane under realistic conditions. Overall, this work established an integrated framework that combined membrane structural engineering, EIS-based monitoring, and adaptive cleaning strategies, providing a viable pathway toward the scalable and sustainable application of MD for oil-containing wastewater treatment.