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Decomposition of Wood in Landfills: Review of Literature

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posted on 2025-01-15, 03:37 authored by Kuluni Piumika MillaniyageKuluni Piumika Millaniyage, Louise WallisLouise Wallis, Nathan Kotlarewski

For decades, landfill-sites have been used as the main disposal method in Australia for wood and engineered wood products. Even though the long-term storage of sawn-wood products in landfill-sites have been reasonably well-documented, knowledge of the carbon in engineered wood products is limited and largely undocumented. Most of the recent research conducted on wood decomposition in landfill-sites are from Australia and the United States. There are mainly two types of methodological approaches used; in-situ landfill-site studies and simulated landfill tests conducted in laboratories. The in-situ landfill-site studies involve excavating the wood waste buried for years in landfill-sites and comparing their relevant parameters against control samples of same wood species (the control samples were obtained from the Forests NSW wood collection in Australian studies) and by analysing the change of chemical composition during decomposition. In laboratory scale studies, wood products are subjected to optimal decomposition conditions in reactors with landfill leachate (the liquid which enters the landfill-sites because of rainfall, surface drainage, groundwater and underground springs, and the liquid generated due to the putrefaction of waste). The loss of carbon is estimated through mass loss and collection of the gas produced.
For greenhouse gas accounting, calculations of emissions from wood are conducted according to the guidelines of the Intergovernmental Panel on Climate Change (IPCC). In comparison to the reviewed papers on in-situ landfill-site studies and simulated landfill studies, IPCC guidelines over-estimate the emissions from wood disposal into landfill-sites. The IPCC’s defined default factor for the “fraction of degradable organic content (DOCf)” for wood decomposition assumes a loss of 50% of the original carbon stored in the wood in landfill-sites. However, recent studies have indicated this percentage to be much lower. IPCC encourages each country to determine their own factors for calculations based on their specific conditions and well-documented research. For instance, The DOCf for wood in Australia’s landfill-sites used in calculations, has been reducing progressively over time (from the generic IPCC factor of 50% used in 2006, to 10% used in 2016 based on published research). Meanwhile, a recent study has suggested the DOCf value of 1.4% for wood in Australian landfill-sites. It is suggested that changing this default factor from 50% to 1.4% for the wood deposited in landfill-sites over a period of 10 years will result in a reduction in estimated GHG emissions on the order of 2.32Mt CO2-e (metric tons of carbon dioxide equivalent). The observations from this literature review also indicate that softwoods generally show lower carbon loss in comparison to hardwoods and that timber species vary in decay based on their anatomical susceptibility to degrade. As indicated in thereferred studies decay levels in landfill-sites for Pinus radiata (Radiata Pine) are quite low. Due to this, studies have not been able to determine if the impregnation of Radiata Pine wood with chemical preservatives had influence on the microbial activity for the degradation of the species in landfill-sites.
In general, most of the wood waste are deposited in construction and demolition landfill sites. The rate of decomposition is noticed to be lower in these sites, due to the limited availability of easily decomposed substrates in comparison with municipal solid waste landfill-sites. Further research about the decomposition of wood on construction and demolition landfill-sites is still required to facilitate the accurate estimation of carbon emissions of wood products in Australia.

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Architecture and Design

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University of Tasmania

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