Effect of sludge concentration on wastewater treatment and membrane fouling control efficiency in electrochemical anaerobic membrane bioreactor

Abstract

This study developed an electrochemical anaerobic membrane bioreactor (E-AnMBR) with a highly conductive membrane anode and evaluated its wastewater treatment performance and membrane fouling control under varying mixed liquor suspended solids (MLSS) concentrations. The system achieved the highest chemical oxygen demand removal efficiency 90.34 ± 4.16% at an MLSS of 5 g/L, which was attributable to a synergy between microbial degradation and membrane retention that was modulated by both the MLSS level and bioelectrochemical processes. As MLSS increased from 5 to 11 g/L, the current output decreased from 0.57 to 0.48 mA, while the fouling rate varied non-monotonically—decreasing from 1.82 to 1.00 kPa/d before rising to 3.96 kPa/d, with the lowest fouling rate observed at 8 g/L. Higher MLSS increased sludge viscosity, impeding electron transfer, reducing current generation, and reducing the electrochemical degradation of extracellular polymeric substances (EPS), thereby accelerating fouling layer formation. Conversely, lower MLSS enhanced current but stimulated microbial EPS production, aggravating fouling. MLSS variations also altered microbial community structure, zeta potential, and particle size, collectively shaping system performance. Fouling modeling confirmed that cake formation and pore blocking mechanisms were consistent across MLSS levels, with differences in fouling rates arising mainly from bioelectrochemical processes that delayed the initiation of these mechanisms. Overall, MLSS concentration modulates membrane fouling in E-AnMBR via combined effects on microbial community, mixed liquor properties, and electrochemical foulant degradation.