Effect of temperature on the permeation for gravity-driven membrane (GDM): Linking adsorbed water with flux decline

The gravity-driven membrane (GDM) system is a promising technology for energy-efficient water treatment. However, there is limited understanding of the influence of water temperature and adsorbed water on GDM performance. In this study, pure water was used to elucidate the coupled behavior and mechanisms of flux decline in GDMs. The results showed that the flux-time profiles of the GDMs followed a similar pattern under all tested conditions, increasing rapidly to a maximum and then gradually declining to a stable flux within approximately 3000 min. When the water temperature increased from 5°C to 35°C, the time required to reach a stable flux decreased to approximately half of that at 5°C. During the permeation process, the ratio of adsorbed water to pore volume (R_a) increased exponentially with time, resulting in a gradual decline in permeation flux from its maximum value to a stable value. Overall, our results indicate that flux reduction in GDM systems is primarily governed by material properties (e.g., surface energy and related interfacial characteristics) and the interactions of water molecules in the adsorbed phase. This work provides mechanistic insights that can guide the optimization of GDM design and operating parameters for energy-efficient membrane treatment systems.