Multifunctional Fe-biochar for simultaneously enhancing methanogenesis and mitigating membrane fouling in anaerobic...

Anaerobic membrane bioreactors (AnMBRs) treating brewery wastewater face bottlenecks of acid inhibition and membrane fouling. In this study, AnMBR with iron-modified biochar (Fe-BC) in-situ addition (FeBC-AnMBR) and conventional AnMBR (C-AnMBR) were compared to systematically evaluate operational performance and elucidate the mechanisms underlying enhanced methane production and fouling mitigation. Results showed that Fe-BC addition reduced volatile fatty acids (VFAs) accumulation by 27.6% and increased methane yield by 39.0%. FeBC-AnMBR exhibited 2.1-fold higher electron transport system activity (ETSA) and 1.6-fold higher Cytochrome c concentration than C-AnMBR, indicating that the enhanced electron transfer capacity accelerated substrate conversion and improved methane yield. This was attributed to the slightly alkaline nature (pH = 8.4), prominent Fe-O bonds, and redox capacities of Fe-BC. Batch experiments confirmed that Fe-BC accelerated bovine serum albumin (BSA), glucose and sodium acetate degradation, with acetate kinase and coenzyme F₄₂₀ activities reaching 300.0% and 142.0% of control levels. Microbial community analysis showed Fe-BC enriched syntrophic bacteria (Syntrophomonas, Syntrophobacter) and methanogenic archaea (Methanosarcina, Methanobacterium). Concurrently, key enzyme genes involved in propionate, butyrate degradation and methanogenesis increased by 13, 8 and 15 copies, respectively, strengthening VFA metabolism and methane synthesis pathways. Membrane fouling was mitigated by a 20.3 kPa reduction in cake layer resistance, an 8.0% increase in sludge particle size, and a 31.0% extension of membrane service life. In summary, Fe-BC improved AnMBR stability and methanogenic performance while mitigating membrane fouling, providing an efficient strategy to increase the operational efficiency of brewery wastewater treatment.