In a recent study published in BiocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More, Disni Gamaralalage, Sarah Rodgers, Andrew Gill, Will Meredith, Tom Bott, Helen West, Jessica Alces, Colin Snape, and Jon McKechnie investigate the environmental and economic benefits of producing biochar from food waste anaerobic digestate. Their research, titled “Biowaste to biochar: a techno-economic and life cycle assessment of biochar production from food-waste digestate and its agricultural field application,” highlights a promising pathway for long-term atmospheric carbon storage and greenhouse gas emission reduction.

The accumulation of food waste presents a significant global challenge, consuming resources and imposing waste management burdens. In the UK, policies are being reformed to standardize waste collection and ensure food waste is managed separately, often through anaerobic digestion (AD). However, the digestate produced from AD often contains plastic contamination, which prevents its direct application to agricultural fields and frequently leads to costly incineration. This incineration not only forfeits nutrient recycling opportunities but also yields minimal net energy recovery due to the digestate’s high moisture content.

Biochar, a carbon-rich material created through pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More, offers a solution for managing wet biogenic wastes like food waste digestate. The study explores hydrothermal carbonization followed by high-temperature post-carbonization (HTC-PC) as an efficient route for producing stable biochar from this challenging feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More. This process is particularly suitable for wet biowastes as it avoids the high pre-treatment (drying) costs associated with other methods like pyrolysis.

The produced biochar demonstrates high long-term stability, with an 88% stable carbon fraction that is resistant to degradation in soil. This stability is crucial for biochar’s role as a long-term climate mitigation tool and aligns with the European Biochar Certificate (EBC) standards. The research indicates that the HTC-PC process sequesters approximately 42% of the initial carbon from the solids in the food waste digestate.

A key finding is the substantial net sequestration of atmospheric greenhouse gases across all scenarios considered. The production and application of one tonne of biochar from food waste digestate result in net emission reductions of 1.15-1.20 tCO2​eq. The largest source of greenhouse gas emissions during the process comes from the oxidation of plastic content in the digestate, releasing fossil carbon as CO2​. However, this is balanced by the significant amount of biogenic carbon sequestered in the biochar.

The economic viability of biochar production from food waste digestate is heavily influenced by the ability to charge a gate fee for processing the digestate. The study found that co-locating biochar production facilities with anaerobic digestion facilities significantly minimizes digestate transport, leading to greenhouse gas mitigation costs of less than £100 per tonne of CO2​eq (125 USD tCO2​eq−1). Without a gate fee, the production costs would be significantly higher, £759 tbiochar−1​ for co-located facilities and £858 tbiochar−1​ when transport is needed, highlighting the importance of the gate fee for commercial viability. Biochar production costs in this study are considerably lower than those reported for biochar from other residue streams or orchard biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More using conventional pyrolysis.

By 2030, if 50% of the UK’s projected available food waste digestate is utilized, it could lead to a sequestration potential of 93 ktCO2​eq per annum, requiring 28 biochar facilities, each with a 20 kt per annum capacity. This represents a significant contribution to the UK’s greenhouse gas removal targets. Globally, if all food waste generated in 2022 (1.05 billion tonnes) were converted to biochar, it could remove 25 MtCO2​eq per annum.

While there are co-benefits to applying biochar to soil, such as improved crop yield and water retention, the study conservatively considered only the avoided NPK fertilizer use due to the release of nutrients from the labile biochar fraction, which had a modest effect on net greenhouse gas removal. Further research is needed to fully quantify these long-term benefits and assess potential technology enhancements to reduce fossil fuel use.

In conclusion, converting food waste digestate to biochar through HTC-PC is a cost-effective and environmentally sound method for carbon removal. The financial success of this approach hinges on minimizing digestate transport through co-location and the ability to charge a gate fee, making it a viable and important strategy for sustainable waste management and climate change mitigation.

Source: Gamaralalage, D., Rodgers, S., Gill, A., Meredith, W., Bott, T., West, H., Alces, J., Snape, C., & McKechnie, J. (2025). Biowaste to biochar: a techno-economic and life cycle assessment of biochar production from food-waste digestate and its agricultural field application. Biochar, 7(1), 50