Biochar production and use: environmental risks and rewards

Biochar is a carbon dense solid that is produced via the pyrolysis of organic materials forapplication to soil. Organic carbon structures, such as those found in animal manures orwood, are modified by exposure to elevated temperatures in an oxygen-limitedenvironment. This processing causes a loss of mass through a preferential loss of hydrogenalong with a loss of volatile carbon molecules. The carbon remaining in the solid formsstable, conjugated aromatic structures, which are more recalcitrant to degradation in thenatural environment than the pre-processed feedstock material. The surface area of thebiochar material is also greatly increased compared to the feedstock, especially at the microporescale. The mineral ash content of the original organic materials is preserved in thebiochar, increasing in concentration with the loss of volatile components of the feedstock.Biochar production and use offers many opportunities for enhancing soil properties andsequestering carbon. The evidence to support the application of biochar as a soilamendment to enhance crop productivity is growing. Its potential as a carbon reservoir, ableto sequester carbon in soils, and hence reduce atmospheric concentrations of greenhousegases is a relatively new area of scientific investigation, on which lies significant sociopoliticalinterest due to the agenda to find cost effective climate change solutions.This thesis makes a significant contribution to the field of biochar production and use indeveloping several aspects of its physical characterization, environmental sustainability,risks, and opportunities. The investigation builds the evidence and methods required tounderstand the potential contribution biochar can make to atmospheric greenhouse gasreduction and agricultural sustainability.Key findings include a comprehensive review of the physical characteristics of biochars andhow they are influenced by processing conditions and feedstocks choice. Also, the discoveryand investigation of Terra Preta Australis sites, which provide an Australian analogy to theTerra Preta de Indio soils, that provide a case study demonstrating the long-term impact onsoil properties and potential for carbon sequestration in that environment. Other majoroutcomes from the work include the development of risk assessment and greenhouse gasaccounting methodologies that can be applied to biochar production and use. Extensivecollaborative work has been included, particularly concerning the agronomic assessment ofa number of biochars derived from commercially relevant feedstocks