Impacts of biogas residual biochar on anaerobic digestion of food waste with different organic loading rate: Methanogenic performance and metabolic pathways

This study investigated the effects of different doses of biogas residue biochar (BRB) (5 g /L and 10 g/L) on the methanogenic performance and metabolic pathways during anaerobic digestion (AD) of food waste (FW) under a wide range of organic loading rate (OLR) (5, 10, 20, and 30 g volatile solid (VS)/L) conditions. The results indicated the cumulative methane yield was highest (375 ± 8.40 mL/g VS) at an OLR of 10 g VS/L when no BRB was added, while suffered significant inhibition at higher OLRs (>10 g VS/L) due to volatile fatty acid (VFA) accumulation. BRB addition (5 g/L) significantly facilitated methane production by first enhancing organic matter degradation and VFA content (days 1–––10), and then accelerating VFA consumption (days 18–––50), with these beneficial effects becoming progressively more pronounced at higher OLRs (>5 g VS/L) in this study. Microbial and metabolic analysis revealed key microbial communities included Aminobacterium , Proteiniphilum , Clostridium_sensu_stricto_1 , Syntrophomonas , and Methanosarcina were enriched, and methanol and methylamine/dimethylamine/trimethylamine methanogenic pathways were enhanced under high OLR conditions with BRB addition. This study provides metabolic flexibility for maintaining stable methane production in response to high OLR while offering a closed-loop solution for digestate valorization.