Efficient methane removal by thermophilic methanotrophs in a compost biofilter

Methane (CH₄) is a potent greenhouse gas, and biofiltration has proved to be a valuable strategy for treating diffuse emissions from composting and landfill systems. This study characterized the activity of a thermophilic methanotrophic consortium enriched from compost. It also evaluated the consortium's performance, under controlled conditions, in a liquid stirred-tank bioreactor and a compost biofilter for 90 and 65 days, respectively. The consortium, specifically the thermophilic methanotroph Methylocaldum, showed robust CH₄ oxidation at 50 °C, attained a maximum elimination capacity (EC) of 342 mg CH₄/kg compost·h with 75% removal efficiency (RE), and maintained an EC of ~250 mg CH₄/kg compost·h from day 28 with 100% RE. Heat treatment of compost followed by inoculation with the methanotrophic consortium enhanced start-up, reduced microbial competition, and improved stability. Oxygen availability and moisture were identified as critical parameters, while nutrient supplementation had minimal effect. Analysis of respiratory coefficients indicated that heterotrophic microorganisms competed for oxygen, influencing CH₄ removal efficiency. Compared with mesophilic systems, the thermophilic biofilter achieved a higher EC, demonstrating the microbes' ability to adapt to higher temperatures. These findings confirm the potential of thermophilic biofiltration for effective CH₄ migration and provide guidance for optimizing design and operational strategies in large-scale applications.