Editorial Feature

What is Biochar?

In the fight to reverse the worsening effects of climate change, there is no one quick-fix idea that will magically save the world. Rather, a combination of methods needs to be utilised and integrated into society.

One such idea that may be used is ‘biochar’. Biochar is essentially charcoal, except it is given different name when used in environmentally oriented applications.

It is formed in roughly the same way, i.e. by the thermochemical decomposition (or pyrolysis) of living or recently living organic material (biomass) in the absence of oxygen. This process has been used for thousands of years to produce charcoal, by burning wood (as other bio waste such as plant stalks and roots). This eventually results in only carbon and inorganic ash. And because there is no oxygen involved in the process, it means that the carbon will not combust.

Remnants of this process are seen in the Amazon rainforest, in the dark soils known as ‘terra petra’. It is thought that ancient Amazonians used a method of pyrolysis to produce better soils for growing crops.

There are numerous benefits of using biochar in everyday applications and also on a larger scale to help significantly reduce carbon dioxide in the atmosphere. Like many clean technology ideas biochar is not a new one – research on its potential started as far back as 1947. However, with the aid of modern practises there has now been resurgence in interest in the potential of biochar.

Carbon Sequestration

The prominent environmental benefit of biochar is that is can trap carbon dioxide and hold it for a long time. Plant material and animal waste will naturally decompose if left alone, and this ends up producing a large amount of CO2 which then becomes a greenhouse gas in the atmosphere. This is of course a natural part of the carbon cycle, but with the huge amount of farming that occurs globally, agricultural waste is a huge contributor to the greenhouse effect via this decomposition.

However, if this waste in converted into biochar, the carbon is locked within it and will not enter the atmosphere. Furthermore, the carbon in biochar is very resistant to degradation, meaning that if this is buried in the ground, it could stay there for centuries. It is thought by using this simple method of creating biochar from farm waste and burying it in the ground, up to 2.2 gigatons of carbon could be stored in the ground by the year 2050. Emissions of nitrous oxide and methane, two more potent greenhouse gases may also be reduced via the production of biochar.

Sewage treatment is also a significant producer of greenhouse gases, but if pyrolysis is used to convert the sewage to biochar, it has been shown that up to 60% of the carbon in the sewage could be locked away.

The entire process ends up being carbon negative and would help to stall the amount of anthropogenic CO2 entering the atmosphere. The technique of burying biochar in the ground can be seen as a form of CDR geoengineering.

Farming Benefits of Biochar

The second independent benefit of biochar is that it makes soil appreciably more fertile. The native tribes of the Amazon still search for ancient ‘terra preta’ because of the fertility of this land. The reason that soil containing biochar is so good for farming is that when the biochar is created, it becomes a highly porous solid, but because of its fine grained nature it is not very permeable. This means that biochar can retain a relatively large volume of nutrients and water within the soil, allowing better crop growth.

Moreover, the good retention of nutrients and chemicals means that biochar use on farmland can lead indirectly to better quality water in the area, as the retention of the chemicals in the soil means that they will not leach into groundwater supplies and cause pollution.

Furthermore, the pyrolysis process can also form biofuels. Biochar is produced at temperatures between 400-500oC, but if biomass is heated to over 700oC, then it can be used to produce syngas, which could potentially be used as fuel.

Limitations of Biochar

One of the prominent issues when discussing biochar production as a large-scale solution to climate change is that there are few financial rewards currently for the production of biochar. Most money in this sector is given out for work involving the production of energy via biowaste, rather than storing it in the ground.

The Royal Society has questioned how effective biochar would be in reducing carbon emissions in the long term and also suggested that widespread production of biochar may inadvertently lead to a rise in food costs and a lack of crops.

Lastly, some people are advocating plantations specifically for the production of biochar, which would be detrimental to local ecosystems and native populations.

Sources and Further Reading

G.P. Thomas

Written by

G.P. Thomas

Gary graduated from the University of Manchester with a first-class honours degree in Geochemistry and a Masters in Earth Sciences. After working in the Australian mining industry, Gary decided to hang up his geology boots and turn his hand to writing. When he isn't developing topical and informative content, Gary can usually be found playing his beloved guitar, or watching Aston Villa FC snatch defeat from the jaws of victory.

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