Critical review on organic fouling in membrane distillation for desalination and water purification

Membrane distillation (MD), a thermally-driven separation technique, with the capability to utilize alternative energy sources and operate effectively in high salinity, brines, and wastewater, has been recognized as an attractive candidate for relieving water scarcity issues. However, membrane fouling caused by the deposition and invasion of foulants on the membrane surface or inside pores has always been a great obstacle constraining the more widespread application of MD in water purification. Although substantial studies have focused on understanding the formation and mechanism of membrane fouling specifically addressing scaling, far too little attention has been paid to the organic fouling during MD process. This critical review first summarizes the common characterization strategies for the investigation of the physicochemical properties of organic fouling. Next, it delves into the water treatment performance and the fouling mechanism under diverse organic matters. We further provide an overview of the significant factors influencing the evolution process of organic fouling during MD. Whereafter, we review the review on methods to mitigate and control organic fouling by pretreatment, membrane material design, and membrane cleaning. Finally, we outline future research directions essential for developing advanced control strategies to mitigate organic fouling, which would contribute to enhancing the efficiency and resilience of membrane distillation. • The influence of organic fouling induced by NOM on MD performance is emphasized. • Invasive and non-invasive characterization techniques for organic fouling are outlined. • The influencing factors and their fouling mechanism are thoroughly discussed. • Pretreatment, membrane modification, and cleaning strategies for organic fouling control in MD are reviewed. • Major challenges, limitations, and future suggestions to organic fouling research on MD are provided.