Fluxes of methane between landfills and the atmosphere: natural and engineered controls

Abstract

Ahtract. Field measurement of landfill methane emissions indicates natural variability spanning more than seven orders of magnitude, from approximately 0.0004 to more than 4000 g m day . This wide range reflects net emissions resulting fiom production (methanogenesis), consumption (methanotrophic oxidation), and gaseous transport processes. The determination of an "average" emission rate for a given field site requires sampling designs and statistical techniques which consider spatial and temporal variability. Moreover, particularly at sites with pumped gas recovery systems, it is possible for methanotrophic microorganisms in aerated cover soils to oxidize all of the methane from landfill sources below and, additionally, to oxidize methane d f i s i n g into cover soils from atmospheric sources above. In such cases, a reversed soil gas concentration gradient is observed in shallow cover soils, indicating bidirectional diffusional transport to the depth of optimum methane oxidation. Rates of landfill methane oxidation from field and laboratory incubation studies range up to 166 g m day , among the highest for any natural setting, providing an effective natural control on net emissions. It has been shown that methanotrophs in landfill soils can adapt rapidly to elevated methane concentrations with increased rates of methane oxidation related to depth of oxygen penetration, soil moisture, and the nutrient status of the soil.Estimates of worldwide landfill methane emissions to the atmosphere have ranged fiom 9 to 70 Tg yr-', differing mainly in assumed methane yields from estimated quantities of landfilled refuse. At highly controlled landfill sites in developed countries, landfill methane is often collected via vertical wells or horizontal collectors. Recovery of landfill methane through engineered systems can provide both environmental and energy benefits by mitigating subsurface migration, reducing surface emissions, and providing an alternative energy resource for industrial boiler use, on-site electrical generation, or upgrading to a substitute natural gas. Manipulation of landfill cover soils to maximize their oxidation potential could provide a complementary strategy for controlling methane emissions, particularly at older sites where the methane concentration in landfill gas is too low for energy recovery or flaring. For the future, it is necessary to better quanti@ net emissions relative to rates of methane production, oxidation, and transport. Field measurements, manipulative studies, and model development are currently underway at various spatial scales in several countries. Introduction and BackgroundGlobal landfilling practices vary widely and are a major determinant of methane generation and emission rates at a given site. At most controlled landfills, rehse is placed in discrete cells covered by replaced natural soils of local derivation; thus it is appropriate to investigate the range of physical, chemical, and microbiological soil processes active in landfill settings. The rates and controlling var...

Seasonal Variability in CH4Emissions from a Landfill in a Cool, Semiarid Climate

“…A nugget effect was observed for the variograms developed from the data for all three seasonal measurements. This suggests that kriging and subsequent contour mapping of CH 4 30 The emission rate observed at the Rooney Road landfill was substantially higher than that found by Bogner et al 11,12 and that for a number of sites in the United Kingdom, particularly those with gas recovery systems. These data are summarized by Bogner et al…”

“…7,[9][10][11][12] This conclusion is supported by stable isotopic measurements of carbon in the emitted CH 4 . 13,14 The work of these authors suggests that perhaps the landfill CH 4 contribution to the atmospheric cycle had been significantly overestimated.…”

“…Bogner et al 7,11,12 found substantial negative CH 4 fluxes over a northeastern Illinois landfill, which had a gas recovery system in operation. The negative fluxes could be the result of negative pressure in the soil pore space and/or the development of a methanotrophic population with extremely efficient CH 4 consumption.…”

Methane Balance of a Bioreactor Landfill in Latin America

“…In very wet landfills, Henry's Law of partitioning of CO 2 to the aqueous phase may promote increases in CH 4 concentration. 13 As LFG migrates, CO 2 may be sorbed. 18 Long transport pathways through water-filled pores can result in fractionation of gas through dissolution of CO 2 into the aqueous phase, whereas less soluble CH 4 remains in the gaseous phase.…”

A Statistical Model for Landfill Surface Emissions

“…These include dynamic or static flux chambers, [1][2][3][4][5] micrometeorological methods, 1,6,7 or pathintegrated optical remote sensing (PI-ORS) techniques. 8 -12 These methods all provide estimates of methane emission levels under the prevailing conditions at the time of measurement.…”