Using Isotopic and Molecular Data To Model Landfill Gas Processes

Abstract

Using a large data set, a preliminary investigation has been made to evaluate the usefulness of stable isotope ratios for improving our understanding of methane and carbon dioxide generation in landfills. Included are approximately 130 landfill gas samples from across the U.S.A., and 18 recent samples from: (1) an Argonne Laboratory study area in the Brea-Olinda Landfill, Orange County, California (U.S.A); and (2) several Los Angeles County landfills, California (U.S.A). The following isotope ratios were examined: δ13C for methane, δ 13C for carbon dioxide and δD for methane. Using simple ratio plots supplemented by mass-balance calculations, these data show promise for indicating the relative contributions of the four major carbon cycle processes in landfills, namely: (1) direct oxidation of organic material to carbon dioxide; (2) methane generation from fermentation (acetate cleavage); (3) methane generation from carbon dioxide reduction; and (4) methane oxidation to carbon dioxide by methanotrophic bacteria. Both the methane generation and oxidation reactions are central to an explanation of the trends discussed herein. The data also suggest that direct oxidation of organic matter in the refuse may be contributing to the observed isotopic ratios in some cases. The trends observed at the Brea-Olinda site were similar to trends using the large U.S. database, suggesting that isotopic techniques may be useful to better constrain carbon cycle processes common to all landfill settings. © 1996 ISWA

Quantifying Methane Oxidation from Landfills Using Stable Isotope Analysis of Downwind Plumes

“…Methane in the anoxic portion of landfills escapes to the atmosphere by flowing through the cover soil cap, through cracks or fissures in the soil cap, and through vents. Several studies on landfills have attempted to determine CH4 flux and oxidation by use of chambers placed over the cover soil, often in conjunction with other techniques such as stable isotopes (11,15,(19)(20)(21)(28)(29)(30)). Yet, it has been hypothesized, based on δ 13 C CH4 balances of landfill emissions, that direct CH4 emissions through cracks, fissures, and vents constitute the primary pathways for gas migration from the landfill system at two European landfills (17).…”