Is application of biochar to soil really carbon negative? The effect of methodological decisions in Life Cycle Assessment

Abstract

One of the proposed solutions for improving soil conditions and mitigating climate change, two of the urgent environmental issues of today, is application of biochar to soil. This carbonaceous material made from a large variety of biomass feedstocks, by several different processes, and at various conditions is envisaged to remain stable in soil for centuries and thus effectively keep carbon out of the atmosphere. Nevertheless, a careful analysis of the entire system of biochar production and application is necessary, before such solutions are applied at a large scale, to avoid creating an even bigger environmental problem. One well-established method to do so is Life Cycle Assessment (LCA). This method has already been applied by many authors to assess biochar-to-soil projects, and based on this literature it appears that biochar application indeed contributes to climate change mitigation. However, even with such a standardized and widely used method like LCA, there are vast methodological differences between the LCA studies. Furthermore, whether the climate impact of biogenic carbon should be considered is an unresolved issue common to all assessments of biomass-utilizing projects. The effects of those and other methodological issues are investigated in the case study of the gasifier in Zlatá Olešnice. The results show that whether a project of biochar application to soil is deemed environmentally beneficial largely depends both on the context of the project as well as the methodological decisions, especially regarding biogenic carbon. Nevertheless, it can be concluded that biochar production from waste feedstock in most cases leads to climate change mitigation.

Keywords: Biochar soil application; Climate change; Gasification; Life cycle assessment; Waste biomass.