Characterizing spatial distribution of fouling on flat-sheet membranes in a pilot-scale gravity-driven membrane reactor for seawater pretreatment

In this study, we investigated the spatial distribution of membrane performance and fouling characteristics in a pilot-scale gravity-driven submerged flat sheet membrane reactor pretreating seawater. After 517 day-operation, the membrane foulants were sampled from the top, middle, and bottom of the flat sheet membrane module. The autopsy of the foulants revealed that more prokaryotes with greater loosely bound extracellular polymeric substances (LB-EPS) and N-acyl homoserine lactone (AHL)-based quorum sensing molecules were deposited on the top of the membrane module, tending to form a cake layer with dense nature. While, more eukaryotes (e.g., Nematoda), tightly bound EPS (TB-EPS), and Fe element were detected on the bottom of the membrane module, resulting in a relatively loose-nature cake layer. Accordingly, the water permeability showed a decreased profile from the bottom to the top of the membrane module. The spatial heterogeneity in permeability and fouling characteristics shed light on the design of large-scale GDM reactors for seawater pretreatment.