Evaluation of respiration in compost landfill biocovers intended for methane oxidation

摘要

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 (CH_4). A laboratory and field investigation was performed to quantify respiration in an experimental compost biocover in terms of oxygen (O_2) consumption and carbon dioxide (CO_2) production and emission rates. O_2 consumption and CO_2 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 CO_2 production and O_2 consumption rates of 107±14gm~(-2)d~(-1) and 63 ± 12gm~(-2)d~(-1) respectively. Gas profiles from the columns showed elevated CO_2 concentrations throughout the compost layer, and CO_2 concentrations exceeded 20% at a depth of 40 cm below the surface of the biowindow. Overall, the results showed that respiration of compost material placed in biowin-dows might generate significant CO_2 emissions. In landfill compost covers, methanotrophs carrying out CH_4 oxidation will compete for O_2 with other aerobic microorganisms. If the compost is not mature, a significant portion of the O_2 diffusing into the compost layer will be consumed by non-methanotrophs, thereby limiting CH_4 oxidation. The results of this study however also suggest that the consumption of O_2 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 CH_4.