Greenhouse gas emissions from first generation ethanol derived from wheat and sugar beet in Germany – Analysis and comparison of advanced by-product utilization pathways

In state of the art ethanol production, by-products like vinasse from sugar beet or distiller’s dried grains with solubles (DDGSs) from wheat grains are usually used as animal feed. The drying process consumes a significant amount of energy that could be reduced by producing other valuable materials or energy carriers from these by-products. Besides resulting higher overall conversion rates and improved process efficiencies, by-products, which can be extracted or are automatically created during the various conversion steps, should be used to reduce environmental impacts as well. In this analysis, advanced pathways for the recovery and use of by-products from bio-chemical ethanol production like gluten separation from wheat starch, biogas production from stillage or vinasse and combustion of bran for electricity generation are analyzed with regard to their contribution to the greenhouse effect. Therefore, different methodological approaches are applied and compared. The analysis shows among others that ethanol from sugar beet generates less greenhouse gases (GHGs) compared to the ethanol production from wheat. The biogas production from residues and especially the use of bran for heat and electricity generation shows significant GHG reduction compared to the state of the art application. However, the methodological approach for the treatment of by-products highly influences the results. For the reproducibility of the results an energy equivalent allocation method involving the specific application of the respective co-product is recommended.