Revisiting the role of EPS in ultrafiltration membrane fouling via LSPR-QCMD and biofilm analysis

Biofouling remains a major limitation in UF membrane performance, with EPS playing a central role. This study employs an integrative physicochemical–biological approach to investigate fouling by EPS derived from biofilms grown in fluidized bed (FLB) and fixed bed (FB) reactors under controlled aquatic conditions. Despite distinct microbial communities, both EPS types exhibited consistent fouling trends, with increasing ionic strength, calcium concentration, and decreasing pH leading to higher fouling. EPS from the FB reactor demonstrated higher fouling propensity, associated with larger molecular size (up to ~3500 kDa), lower negative charge, and a lower protein-to-polysaccharide ratio (i.e., relatively higher polysaccharide content). This compositional shift is consistent with the formation of more cohesive and compact EPS layers. A hybrid LSPR–QCMD approach enabled direct characterization of EPS interfacial properties, revealing a strong correlation between adsorbed dry mass and fouling behavior (R 2 = 0.95, p < 0.001). In parallel, QCMD analysis showed that increased viscoelasticity and reduced hydration of the EPS layer were associated with higher fouling severity, linking EPS composition to interfacial structure and hydraulic resistance. These findings demonstrate that EPS interfacial properties govern UF fouling behavior and that aquatic conditions exert a controlling influence on EPS–membrane interactions. From an engineering perspective, the identified relationships between water chemistry, EPS composition, and fouling provide actionable guidance for optimizing pretreatment strategies and if possible, operating conditions (e.g., ionic strength and pH control), to mitigate fouling in membrane-based water treatment systems.