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Biochar as a soil amendment: Environmental friend or foe?
Citation:
JOHNSON, M. G. Biochar as a soil amendment: Environmental friend or foe? Presented at 5th International Conference on Man and Environment: Enemies or Friends, Pushchino, RUSSIA, June 22 - 24, 2011.
Impact/Purpose:
Pyrolysis to produce biofuels and biochar from biomass is not a new idea, but the use of pyrolysis to extract energy from biomass through a process that can be carbon neutral to carbon negative (i.e., reduces atmospheric CO2) is a novel application of an old technology to a current problem—increasing concentrations of greenhouse gases in the atmosphere.
Description:
Pyrolysis to produce biofuels and biochar from biomass is not a new idea, but the use of pyrolysis to extract energy from biomass through a process that can be carbon neutral to carbon negative (i.e., reduces atmospheric CO2) is a novel application of an old technology to a current problem—increasing concentrations of greenhouse gases in the atmosphere. In pyrolysis, biomass is heated in the absence of oxygen. Pyrolysis produces three possible sources of energy in three different phases (Figure 1). One is combustible gases, or syn-gas (e.g., CO, H2, and other hydrocarbons). Second, is a liquid product known as bio-oil. The third is a solid residue, which is also combustible, known as biochar. The pyrolysis process itself consumes about 15% of the energy contained in the feedstock (Bridgwater, 2006). Syn-gas and bio-oil are both energy rich and may serve as replacement fuels for fossil fuels in various kinds of processes and applications including transportation fuels and biochar, while combustible, may be better suited as a soil amendment to sequester fixed carbon and to improve soil properties (Lehmann, 2007). Carbon yields of biochar range from 20 to 50% of the initial feedstock carbon and depend upon the final pyrolysis temperature, rate of heating and the duration of the pyrolysis. Engineered biochar products produced during pyrolysis can be used as soil amendments for long-term carbon sequestration, while at the same time enhancing and sustaining soil quality and productivity, reducing greenhouse gas (e.g., CO2, NO2, CH4) emissions from soil, and protecting water quality from metals, inorganic nutrients and agricultural chemicals. While attractive it is not clear that adoption of this pyrolysis-biochar system to reduce carbon emissions is without risks to human health and the environment.