Reviving a Remedy

In the past few articles, we have looked at various ways of CDR, such as Carbon Capture and Sequestration (CCS), Direct Air Capture (DAC) and Enhanced Rock Weathering (ERW). Biochar is another such way of removing carbon dioxide from the air, which involves the burning of carbon-rich organic material by the process of pyrolysis (burning in the absence of oxygen). Let us discuss this in more detail.

Biochar: What is it and how does it capture Carbon Dioxide?

We all know that biomass is created when plants use the carbon dioxide in the air by the process of photosynthesis. This is a natural way of removing carbon dioxide from the air. However, when plants die, they decompose and release the carbon dioxide back into the air. To prevent this, biomass is collected from various sources such as Agriculture, Forest, Industrial and Municipal waste and heated at very high temperatures going up to 1000 degrees Celsius. This heating of biomass is done in the presence of little or no air through the process of pyrolysis, and leads to the production of a byproduct called biochar. A small amount of biofuel is also often gathered at the end of pyrolysis.

Interestingly, Biochar is not new, and has been added to soils for hundreds of years by farmers in the Amazon in Brazil and in India. Some examples are that of Raab practiced in Maharashtra in India and Terra Preta in the Amazon basin area of Brazil. Elad, Cytryn, Meller Harel, Lew and Graber, in an article titled The Biochar Effect: Plant Resistance to Biotic Stresses in the journal Phytopathologia Mediterranea in December 2011, have also pointed to the considerable evidence of the use of charcoal or biochar as a soil additive by the pre-Columbian natives of the Amazon basin some 500-2,500 years ago. Similar evidence has been unearthed from Ecuador, Peru, Western Africa, South Africa, Australia and Asia. Another common example of biochar which we notice nowadays is the formation of charcoal after forest fires, which can be easily mixed with manure and applied to the soil.

Biochar is rich in minerals, very porous and a very stable material. It also has a high adsorption capacity. With so much versatility, Biochar has been shown to improve soil nutrition and its water retention capacity. In addition, adding Biochar to soil is an excellent way to sequester carbon for long periods.

In a paper titled A Black Future for Plant Pathology: Biochar As a New Soil Amendment to Control Soil Diseases, published in the Journal Plant Pathology in 2015, Bonanomi, Ippolito and Scala found that Biochar also suppresses airborne and soilborne diseases.

Elad, Cytryn, Meller Harel, Lew and Graber, in the aforementioned article published in December 2011 mention four reasons why there is a renewed interest in Biochar in the 21st century:

• Pyrolysis, the process by which Biochar is produced, will become a tool in reaching net-zero targets by reducing greenhouse gas emissions;
• It can be used as a source of biofuels;
• It can be used as a soil additive that increases soil fertility;
• It can be used as a means to sequester carbon in the soil, since biochar is known to have a half-life of thousands of years depending on the feedstock and the conditions of pyrolysis.

The nature and quality of the biochar also varies depending on the feedstock (whether it was made using forest waste such as wood chips, agricultural waste such as crop residues or municipal waste such as newspapers and food) and the temperature to which it was heated. For example, it has been shown that biochar produced at very high temperatures (greater than 400 degrees Celsius) is very porous and increases soil porosity. On the other hand, Biochar produced at lower temperatures (less than 300 degrees Celsius) has higher cellulose and more nutrients.

Conclusion

Biochar or charcoal is not new and has been used either as a fuel or a soil additive for thousands of years. The recent interest in Biochar in the context of reducing greenhouse gas emissions and carbon sequestration have highlighted the promise of biochar. In addition, the improvement in soil quality and fertility is an added bonus. Given the low usage of biochar in modern agriculture and its proven utility, its awareness and usage should be increased by more support from governments around the world.

The writer is Additional Chief Secretary, Department of Cooperation, Government of West Bengal.
Views expressed are personal