Methanotrophic microbiomes for dilute coal-mine methane biofiltration: ecophysiological constraints and design priorities.

Dilute methane from coal-mine ventilation, drainage systems, and abandoned workings is difficult to treat because low methane partial pressure coincides with high or variable gas flow, short feasible residence times, fluctuating temperature and humidity, nutrient scarcity, and dust or trace contaminants. Aerobic methanotrophs can oxidize methane under moderate conditions, but mine-relevant performance cannot be inferred from isolate activity or gas-phase removal efficiency alone. This Mini Review organizes evidence by coal-mine source class and examines how methanotroph ecophysiology, partner organisms, carrier properties, hydrated biofilm structure, and gas transfer constrain sub-percent methane treatment. Mine-targeted studies comprise laboratory gas-phase reactors, mine-derived enrichments, batch experiments, and recent devices; no long-term validation under authentic mine-gas operation was identified in the targeted literature search. Transferable evidence comes from packed-bed reactors, landfill and compost systems, soils, and defined communities. These studies identify candidate traits that require mine-specific testing, including activity at the target methane partial pressure, recovery after starvation, nutrient economy, attachment, and stress tolerance. We propose source-matched functional microbiomes, activity-resolved methane balances, structured carriers, standardized reactor metrics, and explicit, site-specific no-go conditions as development priorities. Biofiltration should not advance where safe oxygen availability, practicable residence time, acceptable backpressure, or sustainable water and nutrient supply cannot be reconciled with mine operation.