Anaerobic biodegradability of wood: a preliminary review
The literature shows that wood is relatively non-biodegradable in anaerobic environments, though there is a wide variety of results ranging from <2% to 40% of stoichiometric conversion, or roughly <1% to 20% of wood carbon converted to methane carbon. This contrasts with IPCC assumptions that 50% of wood will degrade in landfill environments. The literature results vary with tree species, with wood density (hardwood or softwood), and with particle size. The most reliable and recent laboratory results found 1.5% conversion for softwoods and 6% conversion for hardwoods at <20 mm size, after 1.5 years under ideal laboratory conditions. The only field study of long-term biological decomposition had one site show 20% biological degradation after 46 years, and the other show no detectable (<4%) degradation after 25 years. This review shows relatively strongly that untreated wood degradation in anaerobic environments is best estimated to be 0-20%, or 10% as a good overall estimate, with roughly 5% of the carbon in wood converted to methane. The literature indicates lower anaerobic degradability for pine and eucalyptus wood. At these efficiencies, wood disposed in landfills should be roughly carbon-neutral with the negative of methane production balanced by the positive of carbon sequestration.