Biochar potential in circular economy and as carbon sink

By Maja Berden Zrimec

Biochar, a solid carbon-rich material obtained from the pyrolysis of organic waste, is emerging as a valuable tool for sustainable agriculture, environmental remediation, and carbon sequestration. Biochar is produced through a process called pyrolysis, which involves heating organic waste in the absence of oxygen. This thermal treatment breaks down the waste material and transforms it into a stable form of carbon. Biochar is characterized by its porous structure, high carbon content, and beneficial chemical properties that make it an excellent soil amendment.

Organic waste as a feedstock for biochar production

Biochar can be derived by pyrolysis from a wide range of organic waste materials, including agricultural waste, municipal solid waste, food waste, forestry waste, and industrial waste. These materials can be classified as lignocellulosic materials, which are mainly composed of cellulose, hemicellulose, and lignin. 

From agriculture, crop residues, like straw, husks, and stalks, as well as by-products from agricultural processing, like rice husks and corn cobs, can serve as excellent sources for biochar production. Forestry waste includes wood chips, sawdust, bark, and other residues from forest management and timber processing. This not only helps to recycle and valorise waste from the forestry sector but also reduces the pressure on natural forests for sourcing biochar.

Organic waste from food processing, restaurants, and municipal green waste can also be converted into biochar. This includes fruit and vegetable scraps, yard trimmings, and food industry residues. By diverting this waste from landfills, biochar production contributes to waste management and greenhouse gas reduction efforts. Sewage sludge can be processed by pyrolysis, so there are efforts to include it into the EU Fertilizing Products Regulation by EU fertiliser regulation initiative.

In addition to biochar, pyrolysis produces bio-oil, a complex mixture of organic compounds, including acids, ketones, aldehydes, and phenols, and syngas, a mixture of carbon monoxide, hydrogen, and other gases. Bio-oil can be used as a renewable fuel source, as it has a high energy density and can be burned directly in boilers or used in combustion engines. Syngas can be utilised as a fuel source as well. It has a high energy content and can be used in combustion engines or gas turbines.

Pyrolysis integration into technology streams

The integration of pyrolysis into a company that produces organic waste can be challenging due to the need of specialized equipment and expert operators. The process can be also energy demanding and requires continuous feedstock supply to be cost-effective. Another challenge is common variability of organic waste stream.

Nevertheless, the integration of pyrolysis into a company’s waste management strategy can provide several benefits. It can reduce the volume of waste sent to landfills or incinerators, reduce greenhouse gas emissions from waste disposal, and provide a source of renewable energy or bio-based products. Alternatively, waste can be processed in dedicated pyrolysis facilities or even pilot scale research centres for the lower volumes. For example, Combustion Reduction Integrated Pyrolysis System (CRIPS) is a mobile pyrolysis demonstration unit that can process one-ton of waste organic matter per day.

Benefits and applications of biochar

Biochar’s primary application lies in soil improvement. Numerous studies have shown it has positive impact on soil fertility and plant growth. Soil fertility is improved because of the enhanced water retention, nutrient availability, and microbial activity. Biochar-amended soils have higher crop yields, improved plant growth, and reduced fertilizer requirements (1,2). Use of biochar as a soil amendment is expected to offset many of the problems associated with removing crop residues from the land (2).

Biochar can also be used as a composting additive. Adding biochar to composting processes can enhance the overall quality of the compost. It helps improve moisture retention, increase microbial activity, and enhance nutrient retention in the compost. It can also accelerate the composting process.

Another application on the farms is as bedding material for livestock, by providing a comfortable and odour-reduced environment. Biochar also helps in managing manure by reducing nutrient runoff. 

Biochar plays a crucial role in carbon sequestration efforts because it can act as a long-term carbon sink (2). By converting organic waste into biochar, carbon is locked into a stable form, mitigating greenhouse gas emissions. It has a potential to sequester carbon for hundreds to thousands of years (2,4,5).Promising applications of biochar are expected also in other sectors, like cosmetics, sanitation, construction, food, and medicine as well as high-tech and other industry (6).

VCG.ai role in biochar production from organic waste

Value Chain Generator (VCG.ai) can find links between industries that will enable connections between producers of organic waste and side-streams, and the companies that are able to process the waste to biochar. We are also gathering up the technologies that can be adapted by the waste producers, to process their waste streams on site.

Conclusion

Biochar presents a sustainable solution for waste management, soil enhancement, and climate change mitigation. Derived from a variety of organic waste materials, biochar offers numerous applications, including soil amendment, carbon sequestration, water filtration, and livestock management. Its adoption has the potential to revolutionize agricultural practices, enhance environmental sustainability, and contribute to a greener future.

References

1. Lehmann, J., Rillig, M.C., Thies, J., Masiello, C.A., Hockaday, W.C., Crowley, D. (2011): Biochar effects on soil biota – a review. Soil Biology and Biochemistry 43(9): 1812-1836. Doi: 10.1016/j.soilbio.2011.04.022
2. USDA – US Department of Agriculture – Climate Hubs: https://www.climatehubs.usda.gov/hubs/northwest/topic/biochar
3. Ahmad, M., Rajapaksha, A.U., Lim, J.E., Zhang, M., Bolan, N., Mohan, D., Vithanage, M., Lee, S.S., Ok, Y.S. (2014). Biochar as a sorbent for contaminant management in soil and water: A review. Chemosphere, 99, 19-33.
4. Spokas, K.A., Cantrell, K.B., Novak, J.M., Archer, D.W., Ippolito, J.A., Collins, H.P., Boateng, A.A., Lima, I.M., Lamb, M.C., McAloon, A.J., Lentz, R.D., Nichols, K.A. (2012). Biochar: A synthesis of its agronomic impact beyond carbon sequestration. Journal of Environmental Quality, 41(4), 973-989. Doi: 10.2134/jeq2011.0069
5. Wang, J., Xiong, Z., Kuzyakov, Y. (2015): Biochar stability in soil: meta-analysis of decomposition and priming effects. GCB Bioenergy. Doi: 10.1111/gcbb.12266
6. EBI – The European Biochar Industry Consortium: https://www.biochar-industry.com

Internet sources

EU fertilizing products regulation: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex%3A32019R1009

Sewage sludge for pyrolysis in EU fertiliser regulation initiative: https://www.biochar-industry.com/2023/ebi-position-paper/