| Significant quantities of forest products are discarded in municipal solid waste (MSW) landfills annually in the United States as well as in other countries that depend heavily on landfilling for waste disposal. For example, paper, wood and yard waste comprised approximately 47% of MSW generation in the U.S. in 2012. The anaerobic decomposition of forest products in landfills generates carbon dioxide and methane, and methane is a potent greenhouse gas (GHG). The recalcitrant carbon in forest products that remains after decomposition is considered to be stored.;The objective of this research was to characterize the biodegradability of forest materials that are commonly present in MSW under both laboratory- and field- scale landfill conditions. This information is useful to (a) inform inventories of GHG emissions and carbon storage in landfills; (b) assist in the evaluation of landfill gas to energy projects; and (c) support lifecycle assessments of wood and paper product disposal. In addition, the impact of changes in waste composition on changes in the life-cycle carbon profile of a landfill can be better assessed with waste component specific biodegradability data.;The anaerobic biodegradability of major wood products was characterized by measuring methane yields, decay rates, the extent of carbohydrate decomposition, carbon storage and leachate toxicity. Tests were conducted in triplicate 8-L reactors with red oak, eucalyptus, spruce, radiata pine, plywood (PW), oriented strand board (OSB) from hardwood (HW) and softwood (SW), particleboard (PB) and medium-density fiberboard (MDF). Red oak, a HW, exhibited greater decomposition than either SW (spruce and radiata), a trend that was also measured for the OSB-HW relative to OSB-SW. However, the eucalyptus (HW) exhibited toxicity and no decomposition.;The anaerobic biodegradation of newsprint (NP), copy paper (CP), magazines (MG), and diapers (DP) was studied by measuring methane yields and solids loss, which consistently showed that papers made from mechanical pulps are less degradable than those made from chemical pulps where essentially all lignin was chemically removed. The diaper, which is made from a chemical pulp but also contains some gel and plastic, exhibited limited biodegradability. The extent of biogenic carbon conversion varied from 21 to 96% among papers. A copy paper made from eucalyptus fiber exhibited inhibited decomposition, though this may be due to additives to the paper rather than due to the original source of fiber. The toxicity was partially removed by extraction with how water.;Methane yields, decay rates, solids decomposition and carbon storage factors were also measured for hardwood (HW) and softwood (SW) branches in simulated landfill reactors. The conversions of carbon in HW and SW branches ranged from zero to 28.5%, and HWs exhibited significantly higher conversions than SWs. The lipophilic extractives present in a HW and a SW sample were shown to inhibit methane yields in biochemical methane potential (BMP) tests.;Selected wood and paper products were buried in field-scale landfills and excavated two to three years later to study solids decomposition. A holocellulose decomposition index (HOD) and carbon storage factors (CSFs) were calculated to reflect the extent of solids decomposition and carbon storage. These results, in general, correlated well with the laboratory-scale study, though the decomposition of newsprint and copy paper measured in the field was higher than previously reported.;This research showed considerable variability in the decomposition behavior of various forest products when tested in laboratory-scale high solids reactors that were operated to maximize decomposition. The widely divergent carbon conversions show the limitation of the uniform assumption of 50% DOC f (fraction of degradable organic carbon dissimilated) by the Intergovernmental Panel on Climate Change (IPCC) for biodegradable materials disposed in landfills. |
