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Biochar: A Biomass Product Sinking Greenhouse Gas


 
Biochar, a stable carbon compound, is a charred biomass material. Biochar is produced to sequester carbon and improve soil properties. Biochar is similar to charcoal but the latter is produced mainly for heating purposes [2].
    
Biochar is produced from biomass pyrolysis. Pyrolysis is defined as heating an organic material, in a free-oxygen atmosphere, to a temperature in the range of 400-800oC, with keeping this temperature for a residence time ranging from several seconds to a few hours. To maximize the amount of biochar production from a biomass feedstock, slow pyrolysis in which low heating rates (1-20 oC/min) and long char residence times (a few hours) are applied [3]. In addition to biochar, condensable vapors/liquids called bio-oil and incondensable gases are produced during biomass pyrolysis. Bio-oil contains a wide range of oxygenated compounds. In contrast, combustion is a biomass burning process yielding heat energy and ash that does not contain organic carbon. After biomass pyrolysis, approximately 40% of the carbon contained in the biomass is retained in the biochar. The remaining of the biomass carbon is released as bio-oil and incondensable gases. Part of bio-oil and incondensable gases can be used for operating the pyrolysis process and the excess of these products can be used as a renewable energy source that reduces the dependency on imported oil.
  
Environmental benefits of biochar
Biochar can be applied as a soil amendment. Such application was proposed as an effective tool for carbon sequestration in terrestrial ecosystems and thus reducing the unavoidable greenhouse gases emissions [4]. Carbon sequestration can be explained by the fact that carbon dioxide is used by plants during photosynthesis then when biomass is pyrolyzed the biochar produced is hard to be degraded as compared with the original biomass material. The residence time, in soil, of biochar was estimated to be hundreds to thousands of years and residence time of biomass materials was estimated to be in the range of decades [2]. Therefore, using biochar as a soil amendment could possibly achieve a negative carbon balance and hence it can be a good measure for climate change mitigation. Using forestry and agricultural wastes for biochar production could sequester 0.16 Gt of carbon per year [4]. Land application of bio-char is not new concept. Dark earths “terra preta” was found in the Amazon Basin. These dark earths have received large amounts of biomass burning residues. Studies showed that methane emissions from soils could be completely suppressed after bio-char additions at a rate of 20 g kg−1 soil. Nitrous oxide emissions were reduced by about 50% when bio-char was applied to soil. Moreover, there is a potential to decrease ammonia volatilization from agricultural fields after biochar application due to the fact that biochar efficiently adsorbs ammonia from soil [1].
Economic and social benefits of biochar
In addition to the environmental benefits of biochar production and applications, biochar production systems provide several economic benefits including [2,4 and 5]: (1) renewable energy production from biomass pyrolysis; (2) farmers could reduce the production costs of their crops after applying biochar as a result of increasing crop yields, reduction fertilizer application rates, and reducing the costs and the amount of irrigation water because soil application of biochar enhances water retention capacity specially for sandy soils; (3) biochar can be used as a construction material and a filter medium; and (4) biochar production can create green jobs.
    
  References
  [1] Lehmann, J., Gaunt, J. and Rondon, M., 2006. Bio-char sequestration in terrestrial ecosystems - A review. Mitigation and Adaptation Strategies for Global Change 11(2): 403-427.
[2] Verheijen, F.G.A., Jeffery, S., Bastos, A.C., van der Velde, M., and Diafas, I. (2009). Biochar Application to Soils - A Critical Scientific Review of Effects on Soil Properties, Processes and Functions. EUR 24099 EN, Office for the Official Publications of the European Communities, Luxembourg, 149 pp.
 [3] Brewer, C.E.;  Klaus Schmidt-Rohr,K.;  Satrio, J.A. and Brown, R.C. (2009). Characterization of biochar from fast pyrolysis and gasification systems. Environmental Progress & Sustainable Energy 28(3):386-396
[4] Lehmann, J., Gaunt, J., & Rondon, M. (2006). Biochar sequestration in terrestrial ecosystems- A review, Mitigation and Adaptation Strategies for Global Change, 11, 395–419.
[5] Stein, R.S. and Ely, L. (2011).  Biochar: the countryside combats climate change http://www.mass.gov/Eoeea/docs/doer/renewables/biomass/studycomments/Richard%20Stein_biochar.pdf. Accessed on Feb. 13, 2011
  
  
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