Biochar: A climate solution from the ground up
It is now a foregone conclusion that global warming caused by a buildup of carbon dioxide, the most important climate-warming greenhouse gas humans have been adding to the atmosphere, is, for all practical purposes, irreversible. That is because the current concentration of carbon dioxide will keep the engine of climate change running on a scale of centuries to millennia. As a result, halting our planet from heating up more will be extremely difficult to achieve, unless we go "carbon negative" as soon as possible.
Going carbon negative means removing more carbon dioxide from the atmosphere than adding it. It requires effective use of carbon dioxide removal technologies, such as direct air capture (DAC), or bioenergy with carbon capture and storage (BECCS), or biochar fuel to mitigate residual emissions. A challenge for DAC is that the atmosphere blanketing the Earth is very big, and carbon dioxide is a relatively small part of it, about 0.04 percent. Hence, the technology will work effectively only in the vicinity of power plants where carbon dioxide is emitted in large concentrations. Another area of concern with DAC is energy efficiency. Carbon dioxide is not a very reactive molecule, so extracting it is both energy and resource-intensive.
For all latest news, follow The Daily Star's Google News channel. At its most basic, BECCS involves growing crops, burning them to generate electricity, capturing the carbon dioxide emitted during combustion and storing it deep down into the Earth's crust. However, it is essential to exercise caution to ensure that the emissions resulting from the cultivation, harvesting, transportation, and processing of biomass do not exceed the amount of carbon dioxide captured by the crops. Besides, there are concerns for the safety of the storage of carbon dioxide in huge volumes over a long timescale at a single location due to the possibility of leakages, which can lead to contamination of the environment.
Lately, biochar has gone from being a highly theoretical proposal to being one of the most viable negative emissions technologies. It has gained considerable attention in recent years for its potential to address pressing challenges in agriculture, climate change mitigation, and environmental sustainability.
Biochar is a durable, carbon-rich substance created via pyrolysis, which involves the thermal breakdown of organic materials in an environment with limited oxygen. It has long been recognised for its ability to improve the health of soil and sequester carbon dioxide. Most importantly, biochar can help address climate change because it is one of the several techniques that target carbon dioxide.
As plants grow, they breathe in carbon dioxide from the air, using the carbon they absorb to build their tissues. Then they die and rot or decompose, releasing carbon dioxide into the air again. But if the decomposed plants are turned into biochar, carbon dioxide is instead converted into a solid, which can stay locked in the soil for many years. In this way, plants become one kind of carbon removal engine, drawing climate-warming carbon dioxide out of the air and storing it in the ground.
Biochar can be produced from various types of waste materials, including wood, shells, agricultural residues, and byproducts from industries such as paper mills, sawmills, and breweries, among others. The waste is fed into a special stove-like device called a pyrolyser, a low-tech version like a kiln. Inside the device, the raw materials are deprived of oxygen as they are heated to temperatures between 200 and 700 degrees Celsius. Without oxygen, the wastes cannot catch fire, and their carbon does not turn into carbon dioxide and escape into the air. Instead, the wastes are converted into biochar.
Depending on the operating temperature, the process also yields a liquid called tar or a gas called syngas. These byproducts can be combusted to generate the necessary heat for the continued functioning of the pyrolyser. Consequently, a pyrolyser can sustain its operation or generate additional fuel or energy for commercial purposes.
Once produced, biochar can be added to the soil. It can be applied in various ways, including being sprinkled on the surface, incorporated into the soil in layers or holes, or blended with compost or seeds. The carbon contained in the biochar has the potential to remain in the soil and be sequestered for a prolonged duration. According to Our World in Data, a non-profit online publication that focuses on global problems and trends, biochar can offset the equivalent of up to three gigatons of carbon dioxide each year by 2050, which is like shutting down 800 coal-fired power plants.
The most significant characteristic of biochar is its capacity to enhance the structure of the soil, retain water, and increase the availability of nutrients. It functions similarly to a sponge, effectively retaining vital nutrients and minimising the reliance on chemical fertilisers. Furthermore, its porous structure supports microbial activity, thus promoting healthier soil ecosystems. Biochar presents an environmentally friendly approach to improving characteristics of the soil, especially in sandy, acidic, and nutrient-deficient soils that typically experience challenges with water retention and loss of nutrients.
The production of biochar commonly utilises feedstocks such as rice husks, cassava peels, and various agricultural by-products, which are favoured for their accessibility and effectiveness in generating high-quality biochar. These biochars, sourced from agricultural waste, are particularly valued for their environmental sustainability and low production costs. For example, rice husk biochar is recognised for its ability to enhance the fertility of soil and improve water retention capabilities. Likewise, cassava peel biochar is extensively employed in tropical areas due to its capacity to improve soil structure and nutrient availability. Moreover, biochar derived from agricultural residues like straw, sawdust, and coconut shells is increasingly utilised for sequestering carbon dioxide and enhancing the quality of soil, particularly in regions where the management of organic waste is a significant concern.
The primary obstacle facing biochar is its cost and the fact that it is not a universally applicable solution. Compared to other soil amendments such as fertilisers or compost, biochar is generally more expensive, which complicates its mass production. For biochar to develop into a significant industry capable of contributing meaningfully to the mitigation of climate change, it will be essential to pursue innovative methods that enhance its affordability and efficiency.
Finally, biochar fits the bill kanta diye kanta tola!
Dr Quamrul Haider is professor emeritus at Fordham University in New York, US.
Views expressed in this article are the author's own.
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