A critical review of extracellular polymeric substances (EPSs) in membrane bioreactors: Characteristics, roles in membrane fouling and control strategies

Extracellular polymeric substances (EPSs) are key biological substances, which largely determine properties of sludge flocs, including hydrophobicity, adhesion, flocculation, settling and dewatering properties, and therefore significantly affect membrane fouling in membrane bioreactors (MBRs). Much progress has been achieved in understanding of EPSs and their interrelations with membrane fouling due to a large number of systematic papers published in the last three decades. In this paper, the fundamentals of EPSs including definitions, compositions and properties are summarized. The interrelations of EPSs with other foulants in MBRs are clarified. Roles of EPSs in membrane fouling mechanisms in MBRs are critically assessed. Furthermore, factors affecting EPSs production and characteristics are summarized, and based on which, EPSs control towards membrane fouling mitigation in MBRs are comprehensively discussed. Finally, future research perspectives regarding EPSs and membrane fouling are proposed.