Sequestering Carbon in Landfills: a New Strategy to Offset Greenhouse Gases

Paper and paperboard products accounted for twenty eight percent of the total municipal solid waste generated in the United States in 2009. And while the recovery rate of these products is sixty two percent, the remaining twenty six million tons (38%) represent a potentially useful carbon sink that can be exploited to mitigate the release of greenhouse gases from these landfills. However, to date there are no well established methods for accurately determining the rate and extent of degradation of paper based products and their relative contribution to this landfill carbon sink. During anaerobic microbial degradation of paper based products at landfill sites, the more easily degradable carbohydrate components are lost as methane or carbon dioxide, leaving behind recalcitrant poly-aromatic macromolecules such as lignin. Lignin is a well established plant biomarker that has been extensively used in biogeochemistry to determine the relative amount of terrestrial carbon delivered by rivers to ocean sediments where they are sequestered. Relative lignin concentrations can be determined by thermochemolysis which involves flash heating a sample in the presence of a derivatizing agent such as tetra-methylammonium hydroxide (TMAH) to produce a suite of characteristic phenolic compounds. The sum of these lignin phenols is used to determine lignin concentration. A second approach involves Fourier Transform Infrared (FTIR) spectroscopy which has been explored as a means of characterizing the state of degradation of landfill waste material. However, its success is limited to qualitative measurements. This report summarizes preliminary research aimed at developing thermochemolysis as a quantitative method capable of tracking the rate and state of degradation of paper based products found in municipal waste landfills. These results were qualitatively corroborated by FTIR spectroscopy. Using an anaerobic chamber, 20ml serum vials were seeded with anaerobic sediment and 1cm x1cm pieces of disposable paper plates or paper coffee cups which were previously determined to contain 16.02% and 6.64% lignin respectively. These crimp top vials were capped prior to removal from the anaerobic chamber and placed in a 37 0 C incubator for one month. One vial was sacrificed each week for each paper product and analyzed by thermochemolysis and FTIR spectroscopy. At first glance, compared to the coffee cup samples, paper plate specimens seemed to remain mostly intact for the duration of the incubation. However, after thermochemolysis of the paper plate samples an increase in the average lignin yield from an initial value of 0.71 to 8.93 µg/mg sample dry …