Comparative analysis of membrane fouling in N/P removal MBRs: Linking sludge properties and microbial communities

Membrane fouling is a major challenge for the long-term and stable operation of membrane bioreactors (MBRs). This study systematically investigated the membrane fouling behaviors and mechanisms in three typical MBR systems: a denitrifying phosphorus removal MBR (DPR-AxMBR), an aerobic phosphorus removal MBR (AeMBR), and a denitrifying nitrogen removal MBR (DNMBR). The analysis focused on sludge properties, extracellular polymeric substances (EPS), and microbial community structure to elucidate the influence of different biological metabolic pathways on fouling. The results demonstrated that the DPR-AxMBR system exhibited superior fouling control. The time to reach the critical transmembrane pressure was extended to 137 h, which was significantly longer than that of AeMBR (29 h) and DNMBR (19 h). The DNMBR system experienced the most severe membrane fouling, primarily due to poor sludge settleability, a high accumulation of EPS in the cake layer (59.44 mg/L), and a significant enrichment of fouling-related microbial communities such as Chloroflexi and Acidobacteria. In contrast, the DPR-AxMBR system not only achieved efficient simultaneous nitrogen and phosphorus removal but also significantly mitigated membrane fouling. This was mainly attributed to its relatively low EPS content in the cake layer and the dominance of functional genera like Dechloromonas . This study elucidates the mechanisms of membrane fouling in MBRs from the perspective of the interplay between metabolic pathways and sludge characteristics, providing critical theoretical support for mitigating membrane fouling through process optimization.