Mesophilic Trickle-Bed Reactors for Enhanced Ex Situ Biogas Upgrading at Short Gas Retention Times: Process Performance and Microbial Insights

Biological upgrading of biogas to biomethane is a promising power-to-gas technology with a low environmental footprint. However, due to the lower conversion rates, long-term investigations on mesophilic trickle-bed reactors (TBRs) remain scarce. This study systematically evaluated the performance of lab-scale mesophilic TBRs operated for more than 600 days. A TBR packed with plastic media (Kaldnes K1) consistently achieved methane (CH4) concentrations > 96% at GRTs as short as 2.2 h, and down to 1 h under a mild overpressure (0.1 bar). Mild pressurization (0.1 bar) enabled methane production rates (MPRs) of up to 2.8 NL L−1 d−1 under a hydrogen loading rate (HLR) of 14.9 NL L−1 d−1. At atmospheric pressure, stable MPRs of approximately 2 NL L−1 d−1 were achieved under an HLR of 9 NL L−1 d−1. Microbial community analysis revealed strong enrichment of hydrogenotrophic Methanobacterium (>90% relative abundance) in both suspended and attached biomass, confirming the establishment of a stable methanation pathway. Overall, the results demonstrate that high-rate and stable biomethanation can be achieved under mesophilic conditions at GRTs as low as 1 h, providing new insights for cost-effective biomethane production.