Influence of Carbon-to-Nitrogen Ratio on Two-Phase Anaerobic Digestion in Leach Bed Reactor coupled to Continuous Stirred Tank Reactor: Methane production, Microbial Community and Methanogenic Pathways

The resource utilization of organic solid waste with low carbon-to-nitrogen (C/N) ratios has attracted considerable attention. This study performed dry two-phase anaerobic digestion (AD) on food waste solid residues with varying C/N ratios, and the cumulative methane production at C/N ratios of 11.81, 14.36, and 18.29 was determined to be 137.58, 95.11 and 77.89 mL/g VSadd, respectively. Microbial community analysis revealed that under high ammonia nitrogen (NH4+-N) conditions (>3 g/L), the group with the C/N ratio of 11.89 (G11.89) exhibited potential synergistic effects between Candidatus_Methanoplasma and Methanosarcina, which enhanced methane production rates. However, in G18.29, the addition of fruit and vegetable waste (FVW) induced competitive inhibition of methanogens by nitrogen-fixing microorganisms (e.g., Litchfieldia). This microbial antagonism prolonged the lag phase by 9 days and reduced methane production by 43.39% compared to the G11.89. In summary, FVW addition altered NH4+-N concentrations in the Leach Bed Reactor (LBR) coupled to Continuous Stirred Tank Reactor (CSTR) two-phase system, thereby influencing biomass accumulation. These findings provide valuable insights for optimizing the resource utilization of low-C/N-ratio organic solid waste.