Kinetic and mechanistic analysis of membrane fouling in seawater reverse osmosis: Impact of selective organic foulant retention by membrane-based pretreatments

This study provides a kinetic and mechanistic analysis of how membrane-based pretreatment pore size impacts biofouling in seawater reverse osmosis (SWRO). Untreated raw seawater exhibited a rapid flux decline best described by a cake filtration mechanism (R 2 =0.9094, RMSE=0.0539) due to the co-deposition of large particulates and dissolved organic matter. While conventional microfiltration (MF) removed suspended solids, it allowed low-molecular-weight organics to pass, shifting the fouling kinetics toward internal pore constriction. This structural restriction induced severe hydrodynamic stress on colonizing bacteria, significantly increasing extracellular polymeric substance (EPS) secretion and forming a dense biofilm (146.5 µg/cm²). In contrast, a 0.03 µm ultrafiltration (UF) pretreatment effectively retained critical high-molecular-weight foulant precursors, quantitatively verified by a substantial reduction in the SMP-like organic fraction. This selective retention shifted the SWRO fouling mechanism to complete blocking (R 2 =0.9963, RMSE=0.0108), thereby mitigating the physiological triggers for biofouling and reducing total EPS accumulation to 29.3 µg/cm². Ultimately, this study demonstrates that 0.03 µm UF is a highly effective strategy for modulating fouling kinetics and suppressing the primary drivers of irreversible biofouling, offering a robust approach for sustainable SWRO desalination.