Quantifying methane oxidation in a landfill-cover soil by gas push-pull tests

Area of Science:

• Environmental Science
• Microbiology
• Geochemistry

Background:

• Landfill cover soils host aerobic methanotrophs that oxidize methane (CH4), mitigating atmospheric CH4 emissions.
• Quantifying in situ methane oxidation rates is crucial for understanding landfill gas dynamics and environmental impact.

Purpose of the Study:

• To quantify in situ methane oxidation rates in landfill cover soil using gas push-pull tests (GPPTs).
• To assess the effectiveness of GPPTs for estimating methane oxidation under varying background methane concentrations.

Main Methods:

• Performed multiple GPPTs at two locations within the Lindenstock landfill cover soil over four weeks.
• Injected gas mixtures (CH4, O2, tracers) and monitored breakthrough curves, comparing active oxidation with inhibited tests using acetylene.
• Utilized real-time PCR to confirm methanotroph populations and stable carbon isotope fractionation to verify microbial oxidation.

Main Results:

• Calculated maximum first-order rate constants for methane oxidation: 24.8±0.8 h⁻¹ at location 1 and 18.9±0.6 h⁻¹ at location 2.
• Observed higher background CH4 concentrations at location 2, which sometimes complicated data interpretation.
• Confirmed the presence of abundant methanotrophs and attributed CH4 oxidation to microbial activity.

Conclusions:

• Gas push-pull tests are effective for estimating in situ methane oxidation rates in landfill cover soils, particularly when background CH4 levels are low.
• Methanotrophic activity in landfill cover soils contributes to reducing methane emissions.
• The study highlights the importance of methanotrophs in landfill ecosystems and the utility of GPPTs in their study.