Biopolymer cluster (BPC) in the membrane bioreactor (MBR) treating wastewater and its important role in membrane fouling: A review

Membrane bioreactors (MBRs) have gained prominence in wastewater treatment due to their own merits, yet membrane fouling remains a persistent challenge. While soluble microbial products (SMP) and extracellular polymeric substances (EPS) are recognized as one of critical foulants, their roles in fouling remain contentious. Recent studies realized biopolymer clusters (BPC) as primary drivers of membrane fouling in the MBR. Despite growing evidence of their significance, a unified understanding of BPC’s formation mechanisms, compositional dynamics, and fouling behavior remains elusive. This review synthesizes current knowledge on BPCs, beginning with their ambiguous definition and distinction from SMP/EPS. Formation mechanisms are analyzed alongside environmental triggers such as substrate availability, hydraulic conditions, and microbial community dynamics. Advanced characterization techniques are evaluated for their ability to resolve BPCs' complex structure and adhesion properties. The operational dependencies of BPC accumulation are systematically reviewed to elucidate process-specific fouling patterns. Finally, BPC-targeted mitigation strategies, spanning hydrodynamic optimization, enzymatic disruption, and emerging bio-quorum quenching approaches, are discussed. By bridging mechanistic insights with practical solutions, this review aims to guide future research toward fouling-resistant MBR designs and sustainable wastewater management. • BPC were identified as primary foulant in MBRs in recent studies. • BPC formation mechanisms and compositional dynamics were revealed. • Review integrated qualitative/quantitative insights into BPC fouling behavior. • BPC-targeted control strategies were critically summarized in this review.