Too good to waste: Creating biochar from cleared vegetation as a soil improver and carbon sink
Lyon, K., McHenry, M.P. and Young, N. (2009) Too good to waste: Creating biochar from cleared vegetation as a soil improver and carbon sink. In: Greenhouse 2009, 23 - 26 March, Perth, Western Australia.
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Road construction has a considerable carbon footprint and is likely to be impacted significantly by international and national responses to climate change. Although avoidance of carbon emissions during the design and construction phases is preferred, it is inevitable that some carbon emissions will result in large projects, due to the carbon intensive nature of road construction.
Typical offset projects have focused around the biosequestration of carbon, including large-scale tree planting. Whilst tree planting projects achieve broader benefits from reafforestation, concerns surrounding the biodiversity value of largely monoculture, agro-forestry projects are adding to traditional criticisms such as the measurability and permanency.
Concerns over tree planting as an approach to offsetting have paved the way for consideration of other biological methods for carbon sequestration that are better able to respond to tests of measurability and permanency and attempt to preserve the biodiversity value of cleared land.
Biochar, charcoalised woody biomass, is a soil improver, which is being investigated globally due to its potential to store carbon in the soil for extremely long time periods. On-site production of biochar using cleared vegetation is an approach to carbon offsetting that allows for both the sequestration of carbon in the soil and enhances revegetation activities in the road reserve.
Low technology approaches are practical, using existing road construction equipment to dig pits in which the vegetation is slowly carbonised through low oxygen combustion. High technology but portable approaches for on-site generation using modern biomass to energy conversion technologies (pyrolysis and gasification) are also possible and able to produce biochar and renewable fuels, which can be used in a number of conventional generation technologies such as internal combustion engines and turbines. Roadside vegetation used in modern biomass pyrolysis technologies has the potential to produce around 30 kg of carbon sequestration for each gigajoule of renewable fuel produced.
Biochar may sequester up to 50 per cent of the carbon in the original vegetation, having the potential to become an important part of future revegetation activities in road construction This paper will discuss several approaches to onsite biochar production from road vegetation, in particular a recent trial from Western Australia and the opportunities for reducing carbon emissions and the sequestration of carbon that would otherwise be burnt or left to rapidly decay as chipped or mulched material.
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