Biochar: The Ancient Charcoal

Context: Ancient charcoal, a type of charcoal first used by Amazonian tribes thousands of years ago is becoming a key component of net-zero goals set by blue chip companies eager to offset their carbon emissions.

About Ancient Charcoal: Biochar

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  • Known as biochar, this black substance created by heating biomass and other agricultural waste can store carbon for hundreds of years and improve soil quality at the same time.
  • It is a carbonaceous material derived from waste biomass, of which several key properties, including low bulk density, low thermal conductivity, and the porous nature, have rendered it to present distinguished performance characteristics of the concrete.

How biochar sequesters carbon?

  • It is produced by heating wood and other biomass in a low-oxygen chamber that limits emissions, in a process known as pyrolysis. The bio-oils and gas produced can be used for power generation.
  • The resulting char can be mixed with existing soil, acting as a fertilizer and sequestering carbon with a mean residence time of about 2,000 years.
  • Biochar production and burial remove carbon dioxide directly from the atmosphere through uptake by plants, allowing, in principle, an actual reduction of atmospheric carbon dioxide levels. 
  • By contrast, conventional carbon capture and storage reduces the carbon dioxide concentrations from exhaust fumes, therefore at best preventing atmospheric carbon dioxide levels from rising further. 
  • Biochar is regarded as an ideal material for reducing CO2 in concrete production.

Benefits of Biochar

  • Carbon Sequestration: Potential to sequester up to 2 billion tons of carbon dioxide annually by 2050, or almost as much as India emits in a year.
  • Sound absorption: In addition to its insulation properties, voids and networks of interconnected pores derived from biochar also increase the sound absorption of the concrete. 
  • Cement hydration: The addition of biochar in cement-based composites could increase compressive strength by promoting cement hydration due to its high capacity for water retention.
  • Used as filler: It usually has a fine particle size; thus, it could be used as filler to fill the micropores in construction materials.
  • Fire resistance: Compared to wood-incorporated composites, biochar-modified composites showed relatively high fire resistance due to their stable physiochemical properties.
  • Construction Industry: Utilised as a renewable resource to replace cement content while making mortar that is being used in the construction industry.
  • Water retention: Biochar feedstocks, such as poultry litter and pulp and paper mill sludge, play an active role in enhancing water absorption in concrete.
  • Remediation of Soil: Biochar is often used for the remediation of soil suffering from heavy metal pollution.

Challenges of Biochar

  • Limit activity of earthworms in soil: Due to the application of biochar in soil, the activity of worms reduces which is essential for soil productivity.
  • Soil compaction: The frequent application of biochar causes soil compaction which in return decreases crop yield.
  • Lowers efficiency of pesticides: Biochar also affects the application of pesticides hence reducing the efficiency of pesticides in soil.

About Pyrolysis 

  • It is one of the technologies available to convert biomass to an intermediate liquid product that can be refined to drop-in hydrocarbon biofuels, oxygenated fuel additives, and petrochemical replacements. 
  • It is the heating of an organic material, such as biomass, in low or no oxygen.
  • Biomass pyrolysis is usually conducted at or above 500 °C, providing enough heat to deconstruct the strong bio-polymers. Because no oxygen is present combustion does not occur, rather the biomass thermally decomposes into combustible gases and biochar.  
  • Thus, pyrolysis of biomass produces three products: one liquid, bio-oil, one solid, bio-char, and one gaseous, syngas.

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