Life cycle assessment of wood-based ethanol production at high gravity conditions

Conference poster, 2014

The development of economically feasible and environmentally benign processes for the production of second generation biofuels is an ongoing effort. The production of bio-ethanol from wood (spruce) using high gravity (high solids content) fermentation is one process concept that is currently under development. Such a process will lead to lower water use in the process, and consequently to lower energy use. However, high gravity conditions have adverse effects on the micro-organisms and high yields are thus not guaranteed. All this will affect the environmental impact of the process. Life cycle assessment (LCA) is used to evaluate the environmental impact of the process along its development path. The main objective of the LCA is to help improve the process under development from an environmental point of view. The LCA is based on the results of lab experiments that were done for the high gravity fermentation process using pretreated spruce as the feedstock. These experiments focused on the process configuration and detoxification strategies in order to increase yields. A spreadsheet model was set up that used the experimental data in order to calculate the mass and energy balances of the system under study, from the harvesting of the wood until the produced ethanol leaves the plant (cradle-to-gate). The results of the mass and energy balances were subsequently used in the LCA model in order to calculate the environmental impact of the ethanol production. The outcomes of the LCA for all the process variants studied were compared in order to identify the weak and strong points of the process. This information can then be used for further development of the technology. This poster presents the results of the LCA based on the lab experiments for this wood-based high gravity process under development. Comparisons are made with wood-based ethanol production using a fermentation process at lower solids content, and with ethanol production using first-generation feedstocks and technology. LCA is thus used during the process development and may potentially have a significant influence on this development, and therefore on the sustainability of 2nd generation biofuels that are produced with a high gravity production process.