Scaling in membrane distillation (MD): Current state of art insight on mechanisms and Membrane design

Membrane distillation (MD) process has witnessed significant advancements in research and development since the 1990s, emerging as a viable, cost-effective desalination technology, especially when utilizing waste heat, solar thermal energy, or geothermal heat sources. One of the key challenges hindering MD's broader application is the inorganic scaling of the membranes that form a dense layer on the membrane surfaces, reducing its filtration efficiency, a topic garnering increasing focus in recent studies. Innovative membrane design is now seen as a promising approach to mitigate scaling issues. Yet, the development of ideal scaling-resistant membranes remains an elusive goal, presenting a significant challenge still awaiting comprehensive solutions. This review endeavors to provide an exhaustive understanding of the scaling mechanisms in MD and to formulate a robust theoretical framework for the development of optimal scale-resistant membranes. Such advancements are crucial for enhancing the commercial feasibility of MD technology. This review comprehensively explores established theories and underscores cutting-edge innovations in specific membrane design tactics targeted at scaling mitigation, providing a detailed discussion of morphological tailoring and functionalization strategies for membrane surfaces. Furthermore, it identifies future challenges and potential new research directions in this burgeoning field.