Contribution of specific extracellular organic matter on membrane fouling in ultrafiltration and coagulation-ultrafiltration of algae-laden water

Abstract

This study explores the specific impact of bound and dissolved extracellular organic matter (bEOM and dEOM), and their collective influence with algal cells on membrane fouling during ultrafiltration (UF) and coagulation-UF of algae-laden water. By characterizing the organic properties and adsorptive behaviors of bEOM and dEOM, and analyzing their subsequent impacts, we clarify their roles and contributions to membrane fouling. Our analyses revealed that bEOM, characterized by its higher molecular weight (MW) and hydrophobic nature, contains more protein-like substances compared to dEOM. Quartz Crystal Microbalance with Dissipation (QCM-D) analysis highlights significant differences in their adsorption behaviors, with bEOM demonstrating greater adhesion and higher adsorptive fouling potential. Despite bEOM's lower concentration relative to dEOM, at a ratio of 0.12–1, their contributions to irreversible membrane resistance are nearly identical, at 30.7% and 30.9% respectively, in the UF of algae-laden water. Coagulation pretreatment effectively reduces bEOM's fouling potential by forming larger flocs, thus minimizing its contact with the membrane. In terms of irreversible membrane resistance, the contributions are 6.5% from cells, 24.8% from bEOM, and 68.6% from dEOM. The presence of dEOM complicates coagulation efficiency due to its low MW components and high hydrophilicity. Using the Hermia model, atomic force microscopy (AFM), and scanning electron microscopy (SEM), we demonstrated how bEOM and dEOM modify membrane fouling mechanisms, particularly by influencing cake layer formation. These insights emphasize the distinct and significant contributions of bEOM and dEOM to membrane fouling, necessitating targeted strategies for their management to enhance the efficiency and sustainability of UF systems in water treatment facilities.