Assessing the environmental benefits of biochar application in agriculture: Insights from lifecycle assessment

Organic waste-derived biochar has been proven to have a significant potential for soil improvement, with recent results from this group showing evidence for improved water holding capacity, carbon stability and exchangeable cations. However, to contextualise these benefits it is important to consider environmental impacts during each stage of life cycle for the product. In this study, a cradle-to-gate life cycle assessment (LCA) was performed, comparing a common use for garden organics (composting) to two alternative scenarios. One involved converting over-sized compost screenings (otherwise considered waste) to biochar as a supplementary product from the process, and the other involved converting garden organics directly to biochar as an alternative product. LCA was conducted using ReCiPe2016 impact assessment method in OpenLCA software. Data for assessment were collected from the participating industries and Ecoinvent database. Sensitivity analysis considering different transport distances was carried out and finally an optimum transport distance with the lowest environmental impacts was recommended. Additionally, physico-chemical characterisation and carbon stability assessment were conducted to provide a comprehensive idea about the overall benefits of organic waste-derived biochar for soil and climate. Our results revealed that global warming was increased from 675 kgCO2eq during composting of garden waste to 1017 kgCO2eq where over-sized screenings of compost is converted to biochar as a value-added product. Direct conversion of organic waste to biochar showed reduced global warming impact of 428 kgCO2eq compared to the previous two scenarios. Among 16 environmental impact indicators studied, the magnitude of 10 impact indicators increased with transport distance, while the remaining six indicators were not influenced by transport distance. Soil application of biochar from organic waste has multiple co-benefits, that can be short and/or long term. Nevertheless, this study emphasises that research focused on agricultural application of biochar needs to be coupled with LCA or other holistic assessments for a comprehensive evaluation of net environmental impacts and benefits that consider the processes involved in sourcing of feedstock, biochar production, transport, and application.