Atmospheric emissions and attenuation of non-methane organic compounds in cover soils at a French landfill. Scheutz, C.; Bogner, J.; Chanton, J.P.; Blake, D. R.; Morcet, M.; Aran, C.; Kjeldsen, P..
In addition to methane (CH4) and carbon dioxide (CO2), landfill gas may contain more than 200 non-methane organic compounds (NMOCs) including C2+-alkanes, aromatics, and halogenated hydrocarbons. Although the trace components make up less than 1% v/v of typical landfill gas, they may exert a disproportionate environmental burden. The objective of this work was to study the dynamics of CH4 and NMOCs in the landfill cover soils overlying two types of gas collection systems: a conventional gas collection system with vertical wells and an innovative horizontal gas collection layer consisting of permeable gravel with a geomembrane above it. The 47 NMOCs quantified in the landfill gas samples included primarily alkanes (C2–C10), alkenes (C2–C4), halogenated hydrocarbons (including (hydro)chlorofluorocarbons ((H)CFCs)), and aromatic hydrocarbons (BTEXs). In general, both CH4 and NMOC fluxes were all very small with positive and negative fluxes. The highest percentages of positive fluxes in this study (considering al quantified species) were observed at the hotspots, located mainly along cell perimeters of the conventional cell. The capacity of the cover soil for NMOC oxidation was investigated in microcosms incubated with CH4 and oxygen (O2). The cover soil showed a relatively high capacity for CH4 oxidation and simultaneous co-oxidation of the halogenated aliphatic compounds, especially at the conventional cell. Fully substituted carbons (TeCM, PCE, CFC-11, CFC-12, CFC-113, HFC-134a, and HCFC-141b) were not degraded in the presence of CH4 and O2. Benzene and toluene were also degraded with relative high rates. This study demonstrates that landfill soil covers show a significant potential for CH4 oxidation and co-oxidation of NMOCs.
Methane mass balance at three landfill sites: What is the efficiency of capture by gas collection systems?. Spokas, K.; Bogner, J.; Chanton, J. P.; Morcet, M.; Aran, C.; Graff, C.; Golvan, Y. Moreau-Le; Hebe, I..
Many developed countries have targeted landfill methane recovery among greenhouse gas mitigation strategies, since methane is the second most important greenhouse gas after carbon dioxide. Major questions remain with respect to actual methane production rates in field settings and the relative mass of methane that is recovered, emitted, oxidized by methanotrophic bacteria, laterally migrated, or temporarily stored within the landfill volume. This paper presents the results of extensive field campaigns at three landfill sites to elucidate the total methane balance and provide field measurements to quantify these pathways. We assessed the overall methane mass balance in field cells with a variety of designs, cover materials, and gas management strategies. Sites included different cell configurations, including temporary clay cover, final clay cover, geosynthetic clay liners, and geomembrane composite covers, and cells with and without gas collection systems. Methane emission rates ranged from −2.2 to >10,000 mg CH4 m−2 d−1. Total methane oxidation rates ranged from 4% to 50% of the methane flux through the cover at sites with positive emissions. Oxidation of atmospheric methane was occurring in vegetated soils above a geomembrane. The results of these studies were used as the basis for guidelines by the French environment agency (ADEME) for default values for percent recovery: 35% for an operating cell with an active landfill gas (LFG) recovery system, 65% for a temporary covered cell with an active LFG recovery system, 85% for a cell with clay final cover and active LFG recovery, and 90% for a cell with a geomembrane final cover and active LFG recovery.