Evaluation of respiration in compost landfill biocovers intended for methane oxidation

A low-cost alternative approach to reduce landfill gas (LFG) emissions is to integrate compost into the landfill cover design in order to establish a biocover that is optimized for biological oxidation of methane (CH4). A laboratory and field investigation was performed to quantify respiration in an experimental compost biocover in terms of oxygen (O2) consumption and carbon dioxide (CO2) production and emission rates.

O2 consumption and CO2 production rates were measured in batch and column experiments containing compost sampled from a landfill biowindow at Fakse landfill in Denmark. Column gas concentration profiles were compared to field measurements. Column studies simulating compost respiration in the biowindow showed average CO2 production and O2 consumption rates of 107±14gm−2d−1 and 63±12gm−2d−1, respectively.

Gas profiles from the columns showed elevated CO2 concentrations throughout the compost layer, and CO2 concentrations exceeded 20% at a depth of 40cm below the surface of the biowindow. Overall, the results showed that respiration of compost material placed in biowindows might generate significant CO2 emissions.

In landfill compost covers, methanotrophs carrying out CH4 oxidation will compete for O2 with other aerobic microorganisms. If the compost is not mature, a significant portion of the O2 diffusing into the compost layer will be consumed by non-methanotrophs, thereby limiting CH4 oxidation. The results of this study however also suggest that the consumption of O2 in the compost due to aerobic respiration might increase over time as a result of the accumulation of biomass in the compost after prolonged exposure to CH4.