Biochar promotes methane production from anaerobic digestion: Pore structure regulation and quantitative correlation assessment

As an effective electron-mediating agent, biochar is increasingly utilized to bolster anaerobic digestion (AD) performance. Nevertheless, how its internal porosity influences AD remains unclear. This study synthesized tubular pore modified biochar to optimize AD. Exclusively micro- or mesoporous biochar underperformed due to steric or mass transfer limitations. Conversely, the composite-activator biochar (BC4) featured an optimal mesopore-to-micropore volume ratio of 0.94, increasing methane production by 32.3 %. Pore uniformity significantly correlated with electrochemical capacitance (r = 0.86, P < 0.05), which positively associated with methane production (r = 0.86, P < 0.05). BC4 accelerated organic degradation and short-chain fatty acid conversion, upregulating electron transfer and coenzyme F420 activities by 24.5 % and 29.6 %, respectively. This framework selectively co-enriched Clostridium_sensu_stricto_13 and Methanosarcina, fostering syntrophic metabolism via improved spatial attachment and enhanced electron transfer potential. These findings highlight that synergizing precise pore regulation with favorable surface chemistry is critical for optimizing microbial metabolic networks and maximizing energy recovery.