Characterization and mitigation of membrane fouling induced by extracellular polymeric substances in aerobic granular sludge membrane bioreactors

Extracellular polymeric substances (EPS), key components of aerobic granular sludge (AGS), play a significant role in membrane fouling within AGS-membrane bioreactors (AGMBRs). This study dissected the contributions of soluble EPS (SEPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS) to membrane fouling in AGMBRs, and assessed the effectiveness of an aluminum sulfate/modified microbial flocculant (AS/MMF) pre-coagulation system in mitigating their respective contributions to membrane fouling. The results indicated that the TB-EPS, with its higher protein content, plugged the membrane pores and led to a large accumulation of foulants on the membrane surface, thereby reducing the membrane’s roughness and exhibiting the highest fouling resistance. In contrast, the cake layer formed by SEPS was relatively loose, showing the lowest fouling propensity. Cake filtration was the predominant fouling model. By utilizing the synergistic mechanisms of electrostatic neutralization and adsorption bridging, pre-coagulation significantly increased the zeta potential, inhibited the development of dense cake layers, and reduced both reversible and irreversible resistances. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory further corroborated the effectiveness of pre-coagulation in decreasing the affinity between foulants and the membrane, demonstrating that pre-coagulation could effectively restore the normalized flux, thus providing a new approach for sustainable wastewater management.