COD concentration influence on membrane fouling and microbial communities in A/O-MBR and A/A-MBR systems.

Carbon sources in membrane bioreactor (MBR) significantly affect membrane fouling by influencing microbial metabolic activities, mixed liquor characteristics, and microbial community structure. This study explores the impact of chemical oxygen demand (COD) concentrations (200 and 120 mg/L) on denitrification, phosphorus removal, membrane filtration performance, and microbial community characteristics in anaerobic/aerobic (A/O-MBR) and anaerobic/anoxic (A/A-MBR) systems. Results revealed that higher COD concentrations (200 mg/L) reduced phosphorus removal efficiency and significantly increased extracellular polymeric substance (EPS) production, membrane fouling index (FI), and flux decline rates. Under these conditions, A/A-MBR exhibited lower phosphorus removal efficiency compared to A/O-MBR. Correlation analysis showed strong relationships between FI and EPS relative hydrophobicity (RH), as well as EPS protein content (PN) and Zeta potential, highlighting EPS as a dominant factor in fouling. 16S rRNA high-throughput sequencing further demonstrated that A/O-MBR enriched denitrifying bacteria more effectively than A/A-MBR. These findings suggest that optimising COD concentrations can mitigate fouling and improve overall reactor performance.