Effects of biochar, granular activated carbon, and magnetite on the electron transfer of microbials during the anaerobic digestion process: Insights into nitrogen heterocyclic compounds degradation

Anaerobic digestion (AD) of the hydrothermal liquefaction aqueous phase is often inhibited by high levels of nitrogen heterocyclics, which hinder its valorization. Despite the potential benefits of conductive materials in promoting the degradation of toxic compounds through the establishment of direct interspecies electron transfer (DIET), there is still a gap in the understanding of their role and related mechanisms in nitrogen heterocyclic degradation. In this study, the AD process was improved by the addition of conductive materials. Subsequently, the cumulative methane production increased by 7.2% (with biochar), 15.4% (with granular activated carbon), and 24.3% (with magnetite). Besides, The addition of conductive materials significantly improved the complexity and stability of the microbial communities, especially the DIET potential micro-organisms-Methanosaetaceae and Syntrophobacteraceae, Anaerolineaceae, Clostridiaceae, Geobacteraceae, Desul-fovibrionaceae. Thermodynamic analysis and pyridine degradation pathways further supported enhanced pyridine degradation via the addition of conductive materials.