Micro-gasification: Cooking with gas from biomass - Amper

Micro-gasification: Cooking with gas from dry biomass
What Is Biochar and How Does It Work?
Biochar is found in soils around the world as a result of vegetation fires and historic soil
management practices, used most extensively in the Amazon where it is known as Terra
Preta. Japan also has a long tradition of using charcoal in soil, a tradition that has been
revived and exported over the past 20 years to countries such as Costa Rica. Scientific
investigation of legacy Terra Preta soils in the Amazon, along with recent field and greenhouse
trials, has led to a wider appreciation of biochar‘s unique properties as a soil enhancer.
Biochar has physical, chemical and biological facets which interact to produce a beneficial
impact to soils. Physically, biochar is a very recalcitrant (not easily oxidized or metabolized
by microbes) form of soil carbon with a highly porous structure resulting in a large amount
of surface area where nutrients may be adsorbed and chemical exchanges can take place.
Biochar-amended soils are better able to hold water in drought conditions, have reduced
bulk density, and retain air and other gases. The pores in biochar provide a suitable habitat
for many microorganisms by protecting them from predation and drying while providing
many of their diverse carbon, energy and mineral nutrient needs. Studies of Terra Preta
show a dramatic increase in soil biodiversity compared to adjacent, unamended tropical
soils.
Recent studies have indicated that incorporating biochar into soil reduces nitrous oxide
(N2O) emissions and increases methane (CH4) uptake from soil. Methane is over 20 times
more effective in trapping heat in the atmosphere than CO2, while nitrous oxide has a global
warming potential that is 310 times greater than CO2. Although the mechanisms for
these reductions are not fully understood, it is likely that a combination of biotic and abiotic
factors are involved, and these factors will vary according to soil type, land use, climate and
the characteristics of the biochar. An improved understanding of the role of biochar in reducing
non-CO2 greenhouse gas (GHG) emissions will promote its incorporation into climate
change mitigation strategies.
Biochar can be an important tool to increase food security and cropland diversity in areas
with severely depleted soils, scarce organic resources, and inadequate water and chemical
fertilizer supplies. Biochar provides a unique opportunity to improve soil fertility for the long
term using locally available materials. Used alone, or in combinations, compost, manure
and/or agrochemicals are added at certain rates every year to soils, in order to realize benefits.
Application rates of these can be reduced when biochar is a component of the soil.
Biochar remains in the soil, and single applications can provide benefits over many years.
International Recognition of Biochar Potential for Climate Mitigation and Food Security
In 2008 and 2009, leading up to the Copenhagen climate meeting, multiple countries and
the UN Convention to Combat Desertification (UNCCD) made submissions in support of
biochar to the UNFCCC. The countries include Micronesia, Belize and a consortium of African
governments (made by Swaziland on behalf of Gambia, Ghana, Lesotho, Mozambique,
Niger, Senegal, Swaziland, Tanzania, Uganda, Zambia, and Zimbabwe). The submission
by Belize suggested the need to develop global baselines of soil carbon pools, and monitoring
systems that will allow soil carbon improvements based on the use of biochar as a soil
amendment for mitigation and adaption, under the existing Clean Development Mechanism
(CDM) and under other mechanisms that may be considered in the future. The joint submission
by the consortium of African governments signaled a desire to include the potential
of dryland soils in sequestering carbon, including with the use of biochar. The submission
highlighted ―the intricate linkages between climate change and frequent and severe droughts,
land degradation and desertification,‖ and its particular impact on developing countries,
the poor and vulnerable inhabitants of dryland areas.
The submission from the Federated States of Micronesia noted that biochar also has potential
as a ―fast-start‖ strategy to mitigate climate change in the immediate near-term. For in-
HERA – GIZ Manual Micro-gasification Version 1.01 January 2011
95