Innovations in Measuring Field Scale Biological Methane Oxidation at Two Soil-Covered Closed Landfills

One of the most promising and cost-effective options for control of low-level methane (CH4) emissions is the use of engineered bio-based systems. It has been proved that in landfill cover soil, micro-organisms remove CH4 from Landfill Gas (LFG) as the gas migrates through aerobic regions above the buried waste. However, one of the main issues delaying the field implementation of such techniques capable of reducing CH4 emissions from landfills is the lack of a proper field technique to assess the level of CH4 oxidation under field conditions. Only specialized Stable Isotope (SI) based methods are capable of such a task. Gas Push Pull Test (GPPT) method was developed and used to assess in-situ methane oxidation in two low-emitting closed landfills. Simple interpretations of the GPPT data was developed. Stable carbon isotope data was also obtained in conjunction with the GPPTs which provides an independent verification of CH4 oxidation. The GPPT analysis yielded an average percent oxidation of 40 and 52% for the two closed sites. The GPPT methane oxidation results agreed with the SI based values obtained from 20 above ground air samples from each of the closed sites. The study suggests that GPPT can be easily used to as-sess methane oxidation in in the field. Additionally, the results of the GPPT and the Isotopes analysis were lower than the overall oxidation rates estimated from the modeled generation and the measured tracer-based total emissions testing performed at the two landfills.