Graphitized Biochar Derived from Agricultural Wastes Enhances Methanogenesis via Conductivity-Driven Direct Interspecies Electron Transfer.

Biochar has emerged as a promising conductor for facilitating direct interspecies electron transfer (DIET) in anaerobic digestion (AD), yet the mechanisms linking its structural features to methanogenic performance remain unclear. Here, how feedstock type and pyrolysis conditions modulate biochar conductivity and consequently shape methanogenic pathways is investigated. Using straw, wood, and nutshell-derived biochars, nutshell biochar pyrolyzed at 550 °C(CC550) is demonstrated to achieve the highest methane yield, enhancing production by 59% compared to the control and outperforming straw and wood-based biochars by 12% and 5% respectively. Graphitization analysis confirms that high electrical conductivity is key to accelerating methanogenesis. Metagenomic profiling reveals that CC550 enriches cellulose-degrading bacteria and DIET-associated taxa, while upregulating genes related to pili and cytochrome c expression, promoting acetoclastic methanogenesis through enhanced electron flow. These findings highlight the role of graphitic biochar as a metabolic modulator in AD and offer insights for engineering carbon materials to optimize bioenergy recovery from organic waste.