Enhanced methane production and biofouling mitigation by Fe₂O₃ nanoparticle-biochar composites in anaerobic membrane...

Conductive materials present an innovative approach to enhancing methane production while facilitating sludge reduction and recovering resources in anaerobic digestion systems. However, the synergistic mechanisms by which composite materials influence the performance of anaerobic membrane bioreactor (AnMBR)-particularly in improving methane production and mitigating membrane fouling, remain underexplored. To address this, Fe₂O₃ nanoparticle-biochar composites (Fe₂O₃-BC) were synthesized to enhance electrical conductivity and promote efficient electron transfer in AnMBRs system. These results demonstrated that Fe₂O₃-BC exhibit high electron donor and electron acceptor capacities, increasing electron transport system (ETS) activity and conductivity by 1.4-fold and 1.7-fold, respectively. This enhancement accelerated the degradation of organic matter during the hydrolysis-acidification stage and boosted the activity of key enzymes (CytC and F420) in the methanogenic phase, resulting in a 42 % increase in methane production. Microbial community analysis indicated that Fe₂O₃-BC strengthened the methanogenic pathway by fostering efficient metabolic interactions between acidogenic bacteria (e.g., norank_f_Rikenellaceae) and methanogens (e.g., Methanosaeta). Long-term experiments with the Fe₃BC₂₅-AnMBR reactor showed a significant reduction in the accumulation of soluble microbial products (SMP) and extracellular polymeric substances (EPS) on membrane surfaces, along with a decline in fouling-related bacteria (e.g., Bacteroidota), mitigating membrane fouling by approximately 20-65 %. Furthermore, Fe₃BC₂₅ inhibited biofilm-related quorum sensing (QS) signals (e.g., C6-HSL, AI-1, and AI-2), reducing microbial adhesion and biofouling. Simultaneously, it enhanced methanogenesis by upregulating QS signals associated with methane production (e.g., C10-HSL). Fe₂O₃-BC is expected to offer a promising strategy for advancing energy-driven AnMBR processes.