A comprehensive review of vacuum membrane distillation: Applications, challenges, and future directions

This comprehensive review critically evaluates recent advances in Vacuum Membrane Distillation (VMD) for water and wastewater treatment, systematically analysing developments since the last review dedicated to VMD in 2017. Our analysis reveals wide variations in VMD energy performance, with the system reaching a promising gained output ratio (GOR) of 0.9. Improvement could be achieved through multi-stage and hybrid systems, renewable energy integration, novel localised heating, and heat recovery, potentially increasing GOR above 3. Our comprehensive assessment of conventional and submerged VMD systems across diverse feedwaters demonstrates remarkable contaminant rejection exceeding 99 % for non-volatile contaminants, with emerging potential for treating challenging wastewaters containing microplastics and pharmaceuticals – an area we identify as critically underexplored. This review examines membrane fouling and wetting, significant barriers to VMD commercialisation, and explores mitigation strategies including pre-treatment processes, membrane modifications to enhance hydrophobicity, and process optimisations. Based on our critical evaluation, we identify key research priorities: enhancing energy efficiency through innovative designs, deepening understanding of fouling and wetting mechanisms with real wastewaters, and developing robust mitigation strategies. Pilot-scale studies, comprehensive life cycle assessment and economic analysis are all crucial for evaluating the long-term performance, feasibility and environmental impact of VMD systems. Addressing these aspects could significantly further the advancement and broader adoption of VMD, especially where conventional technologies face limitations. • VMD applications and key operational challenges are critically reviewed. • Hybrid, multi-stage system and latent heat recovery enhanced VMD energy efficiency. • Conventional and submerged VMD showed promising results across diverse feedwaters. • Membrane fouling and wetting, and mitigation strategies applied in VMD are highlighted. • Future directions and perspectives for the VMD applications are outlined.