Potential of biogas residue biochar modified by ferric chloride for the enhancement of anaerobic digestion of food waste.

Biogas residue biochar (BRB) and BRB modified by ferric chloride (BRB-FeCl3) were applied to promote anaerobic digestion (AD) of food waste (FW), related mechanisms were also proposed in this study. Results indicated BRB-FeCl3 showed higher specific surface area, more abundant functional groups and impregnate iron than BRB, and they respectively increased 22.50% and 12.79% cumulative methane yields compared with control group because of accelerated volatile fatty acids (VFAs) transformation, which were confirmed by enhanced metabolism of glycolysis, fatty acid degradation and pyruvate. BRB, especially BRB-FeCl3 facilitated the growth of Syntrophomonas, Methanofollis, Methanoculleus and Methanosarcina, which further promoted the methanogenesis by enhancing the metabolic activities of methanol, dimethylamine and methylamine pathways, thereby causing more metabolically diverse methanogenic pathways. Metagenomics analysis revealed BRB, especially BRB-FeCl3 promoted the relative abundances of functional genes involved in direct interspecies electron transfer (DIET). Present study explored the enhancement mechanisms and feasibility of BRB-FeCl3 for AD process.