Exploring low-concentration methane oxidation: Insights from bioengineered column experiments

Methane is a potent greenhouse gas with a significant impact on climate change due to its high-warming potential, despite its relatively low atmospheric concentration compared to carbon dioxide. For this reason, research on methane mitigations is particularly relevant for industrial applications, as flue gas emissions from plants often contain small amounts of methane (below 10000 ppmv), and their removal using physicochemical methods could be cost-prohibitive. Utilizing biochar-amended soils could effectively remove these trace methane emissions, contributing to greenhouse gas reduction efforts, while providing strong financial incentives for industries to adopt such mitigation strategies. The study prepared soils amended with 20 % and 40 % biochar made from recycled wood, measuring various soil properties and using two acrylic columns to conduct experiments with a continuous methane supply, later reducing the flow and adding nutrients to enrich methane-oxidizing microorganisms. The study found biochar amendments improved soil properties, creating a favorable environment for methanotrophs, and significantly increased methane oxidation rates after adding nutrients. The average methane removal efficiencies were 65 % and 60 % during the study period (between 22nd to 50th days) and maximum methane removal efficiencies were 80 % and 78 % for 20 % and 40 % biochar-amended columns, respectively, with qPCR analysis revealing a high cell count of methane-oxidizing bacteria (∼3.4 ×10⁷ cells/gm soil). A one-dimensional convective-dispersive solute transport model was used to estimate methane concentration at various column heights at different times. The model results were validated with experimental results and significant agreement was found (R²>0.8). Our findings underscore the potential of biochar-amended soil as a viable tool for enhancing methane oxidation in low-concentration environments, offering a practical approach to reducing methane emissions and complying with new regulatory requirements.