Biogas plants as a future opportunity towards material and energy use of CO2 - an LCA perspective

In Germany, there has been significant growth in the development of biogas plants and biogas has different applications in industry in its raw state. Furthermore, when subject to upgrading processes to obtain pure methane (biomethane) and pure carbon dioxide (biogenic CO2), its utility expands considerably. However, the CO2-rich gas stream is often neglected as a useful by-product and instead treated as emission, contributing to an estimated release into the atmosphere ranging from 3.9 to 16.2 Mt/yr. This study aims to provide a comprehensive Life Cycle Assessment (LCA) model for the evaluation of biogenic CO2 production chains of industrial-scale biogas plants in Germany. The study resulted in a ready-to-use parametrized LCA-model encompassing the whole value chain from substrate cultivation and collection, substrate fermentation, biogas cleaning, biogas upgrading, biomethane compression, and CO2 liquefaction. The model also accounts for various possible combinations of treatment technologies and process chains and hence enables a scenario analysis and the identification of environmental impacts of potential production chains. Furthermore, it guides the biogas industry to integrate CO2 capture into their process, support with resilient environmental data and thus enhance process circularity while substituting fossil reference products.