Bio-energy in the Black

Bio-energy in the Black
Johannes Lehmann, Frontiers in Ecology and the Environment, 2007

Abstract
Common renewable energy strategies can at best off-set fossil fuel emissions of carbon
dioxide, but are not able to reverse climate change. One promising approach of lowering
carbon dioxide in the atmosphere while producing energy is bio-char bio-energy based on
low-temperature pyrolysis. This bio-energy technology relies on capturing the off-gases
from thermal decomposition of wood or grasses to produce heat, electricity or bio-fuels.
Bio-char is a significant by-product of this pyrolysis with remarkable environmental
properties. Bio-char in soil was shown to persist longer and to retain cations better than
other forms of soil organic matter. The precise half-life of bio-char is still disputed,
however, and will have important implications for the value of the technology including
carbon trading. In addition, the cation retention of fresh bio-char is relatively low
compared to aged bio-char in soil and it is not clear after what period of time and under
which condition bio-char attains its adsorbing properties. In order to maximize the
favorable attributes of bio-char and fully evaluate environmental risks, research is needed
at this critical juncture in the development of a bio-char bio-energy technology that has
the potential to provide a significant carbon sink and to reduce environmental pollution
by fertilizers.

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p>In a nutshell:
• Current approaches to replace fossil fuel with renewable energy at best reduce
emissions, but are unable to reverse climate change.
• A new strategy obtains energy from gases produced by thermally degrading trees,
shrubs, grasses, or organic wastes - very similar to charcoal making - in a process
called pyrolysis. Charcoal or “bio-char” is left behind.
• The proposed approach to combine pyrolysis for energy production with bio-char
additions to soil builds on its proven longevity and ability to retain cations better
than other forms of carbon in the environment to actively draw carbon-dioxide
from the atmosphere, regenerate degraded lands, and reduce environmental
pollution.
• Precise knowledge of the longevity of bio-char and of the time and conditions to
develop adsorptive properties is needed to evaluate its economic and
environmental benefits.
• A full environmental risk assessment needs to be conducted to convincingly
demonstrate the level of emissions and lack of any soil contamination associated
with the technology.