Long-term performance of thermoacidophilic methanotrophic biotrickling filters

This study investigated thermoacidophilic biotrickling filters (BTFs) for methane mitigation under acidic (pH 2.2–2.5) and thermophilic (45 °C) conditions. Four laboratory-scale BTF reactors were operated over ∼700 days under anaerobic, microaerobic, and aerobic regimes to evaluate the enrichment, activity, and stability of methane-oxidizing microbial communities. Following an initial establishment phase, biofilms developed successfully on pumice packing, with methane elimination capacities (ECs) reaching 41.9 ± 2.6 g m -3 h -1 under microaerobic conditions (1%–3% O 2 ). Aerobic reactors achieved maximum ECs of 30.7 ± 2.4 g m -3 h -1 , while performance declined at higher methane loading rates, likely due to oxygen limitation and accumulation of inhibitory intermediates such as formic acid. Microbial community analysis revealed persistent dominance (47%–99%) of the thermoacidophilic methanotroph Methylacidiphilum , despite their low initial abundance in the geothermal soil inocula. Reactor performance varied with time, driven by nutrient availability, biofilm accumulation and mass transfer limitations, including liquid channelling and bed flooding. Elevated CO 2 recovery (>100%) and O 2 consumption indicated a possible shift towards endogenous carbon metabolism and potential syntrophic interactions within the community. Additionally, iron dissolution within reactors supported the proliferation of iron-cycling acidophiles. Overall, this work demonstrates, for the first time, long-term operation of thermoacidophilic methane-removing BTFs and highlights their potential for treating hot, acidic gas streams such as landfill biogas and geothermal emissions.