“Biochar bridges the gap between old and new. Centuries or even millennia ago, indigenous farming communities in the Amazon rainforest were producing biochar by smouldering biomass in pits or trenches. This char is one of the defining constituents of terra preta (Portuguese for “black earth”) – the dark soil found in the Amazon Basin, renowned for its fertility. Although terra preta has existed for a long time, it is only within the past decade or so that biochar and its myriad of beneficial effects have received scientific interest. To further illustrate this point, a quick search for “biochar” in Google Scholar yielded 77 results for the year 2000, 1,730 results for 2010 and 38,900 results for 2020.

It appears that over the last decade, biochar has seen a remarkable surge in interest. But what precisely is the reason behind its growing popularity? In the following paragraphs we aim to address just that.

What is biochar?

The International Biochar Initiative (IBI) defines biochar as “a solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment”. In other words, an organic feedstock such as wood, manure or leaves is heated to a temperature between 300°C and 800°C, with very little oxygen present. This process, referred to as pyrolysis, produces biochar, a charcoal-like by-product rich in stable carbon. Yet, biochar differs from charcoal, which is mainly used as a fuel, in that its primary applications are in agriculture, horticulture and related fields.

Among the key physicochemical properties of biochar are its porous structure and high surface area. Typically, biochar boasts a surface area of 100-500 m²/g. As such, a single gramme of char has roughly the same surface area as a doubles tennis court. Furthermore, biochar has a high number of functional groups on its surface. Due to these characteristics, it can retain water and nutrients as well as adsorb environmental pollutants. It also offers a suitable growing environment for many beneficial microorganisms.

An additional key attribute of biochar is its permanence. The carbon in biochar is highly stable and can endure in soil for hundreds or thousands of years without being degraded by microorganisms. Thus, biochar represents a long-term CO₂ sink that can sequester carbon in the soil virtually indefinitely. This makes biochar a promising Carbon Dioxide Removal (CDR) technology that can contribute to the mitigation of climate change. CDR technologies are becoming ever more important as countries worldwide are getting serious about meeting their net zero targets.

Exploring biochar’s potential

The multifaceted benefits of biochar include diverse applications, many of which are outlined below. However, the list is not exhaustive:

Soil enhancement: the best-known application for biochar is its use in soil improvement. When applied directly to agricultural or horticultural soils or other green areas, biochar is believed to increase crop yields and soil quality due to its ability to retain water and plant nutrients, loosen soil structure, and initiate humus formation. In addition, it can also bind nitrogen compounds such as ammonia and nitrate and prevent their leaching into the groundwater, making them available for plants instead, which require nitrogen for development. Biochar thus reduces the need for mineral fertilisers in agriculture.

Feed additive: biochar is already in use as a feed additive for a range of farm animals including cows, pigs and poultry, where it can prevent or treat digestive problems. This leads to improved feed conversion and hence to faster weight gain and better meat quality. The resulting biochar-enriched manure can be spread on arable land for enhanced crop production. Biochar acts as a carrier for plant nutrients and thus improves the effectiveness of manure from biochar-fed livestock.

Biogas plants: anaerobic digestion (AD) is a biological process through which microorganisms digest organic materials such as food waste, farm manure, or sewage sludge, and turn it into biogas and biological fertiliser. AD plants face multiple challenges, including process instability and low biogas yields. With its large surface area, biochar not only provides a substrate for the growth of beneficial microorganisms but also adsorbs inhibitory substances, thereby stabilising the digestion process and increasing biogas yields. Lastly, it can enhance the effectiveness of the AD digestate as a fertiliser.

Biochar also has additional uses outside of the agriculture sector, including in urban green spaces, soil remediation, water filtration and decontamination, and as an additive in construction materials, plastics and textiles.

Carbon sequestration strategies: the biochar connection

Anthropogenic climate change is driven by increasing amounts of CO₂ in the atmosphere. Since the carbon in biochar is stable, biochar production can be used to sequester it in the soil for vast periods of time, thereby contributing to climate change mitigation. The carbon sequestered in biochar can be represented and traded in the form of carbon credits. These credits can be purchased by environmentally conscious companies to offset their carbon emissions. At the time of writing, one tonne of biochar-based carbon fetched between €100 and €500 on the voluntary carbon trading platform Puro.Earth. The additional income from carbon credits can enable biochar makers to offer their product at a lower price, thereby contributing to the economic viability of the biochar industry.

What does the regulatory landscape look like?

Biochar is a relatively new but rapidly growing industry that is expected to play an important role in the decarbonisation of the economy. Due to the novelty and current small size of the sector, in most European countries there is as yet no legislation dealing specifically with biochar. However, biochar has recently been approved as a fertiliser in the EU, which is one of a number of developments that are expected to boost the biochar industry.

In terms of biochar production, at present the most relevant certification system for biochar in Europe is the European Biochar Certificate (EBC) which includes specifications on permitted feedstocks, material characteristics, limits for problematic substances and production and use requirements. This provides certainty to biochar buyers that the product they are purchasing has been produced sustainably and satisfies the rigorous EBC quality standards. Consequently, many biochar manufacturers pursue efforts to obtain EBC accreditation for their product, but participation in the scheme is voluntary and does not form part of biochar legislation (if any).”

About Carbogenics

At Edinburgh-based cleantech company Carbogenics, we are on a mission to bring the many benefits of biochar to farms and other agricultural businesses across the UK. For more information, please visit our website or contact Lucy Chappel.

Disclaimer

The information presented herein is relevant at the time of writing, is of a general nature and is not intended to address circumstances of any particular individual or entity.

Please note, the opinions expressed in this article are the author’s own and do not necessarily reflect the views or opinions of CHAP.

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