Boosting water flux in gravity-driven membrane filtration: Impacts of relaxation strategies, module configurations, and feed water characteristics

Gravity-driven membrane (GDM) filtration is a low-energy water purification technology, but its broader adoption is often limited by low water flux. This study addresses this challenge by investigating the effects of relaxation strategies (varying durations and frequencies), module configurations, and feed water characteristics on flux behavior and fouling layer characteristics. Experiments using river water revealed significant flux enhancements (up to 528 %) with longer relaxation and less frequent daily cycles compared to without relaxation. These enhancements were linked to the development of a more porous fouling structure (up to 120 %) and a reduction in irreversible membrane fouling (up to 80 %). Module configuration also played significant role, with external modules displaying thinner fouling layers (up to 90 %) and fewer foulants (up to 36 %). Additionally, feed waters containing natural bacteria and eukaryotes exhibited sustained flux enhancements over time under application of daily relaxation. The findings highlight the potential of optimized daily relaxation combined with external module to significantly improve flux performance during GDM treatment of waters with natural microbial communities.