Abstract
BackgroundDevelopment of more sustainable biofuel production processes is ongoing, and technology to run these processes at a high dry matter content, also called high-gravity conditions, is one option. This paper presents the results of a life cycle assessment (LCA) of such a technology currently in development for the production of bio-ethanol from spruce wood chips.ResultsThe cradle-to-gate LCA used lab results from a set of 30 experiments (or process configurations) in which the main process variable was the detoxification strategy applied to the pretreated feedstock material. The results of the assessment show that a process configuration, in which washing of the pretreated slurry is the detoxification strategy, leads to the lowest environmental impact of the process. Enzyme production and use are the main contributors to the environmental impact in all process configurations, and strategies to significantly reduce this contribution are enzyme recycling and on-site enzyme production. Furthermore, a strong linear correlation between the ethanol yield of a configuration and its environmental impact is demonstrated, and the selected environmental impacts show a very strong cross-correlation (r^2>0.9 in all cases) which may be used to reduce the number of impact categories considered from four to one (in this case, global warming potential). Lastly, a comparison with results of an LCA of ethanol production under high-gravity conditions using wheat straw shows that the environmental performance does not significantly differ when using spruce wood chips. For this comparison, it is shown that eutrophication potential also needs to be considered due to the fertilizer use in wheat cultivation.ConclusionsThe LCA points out the environmental hotspots in the ethanol production process, and thus provides input to the further development of the high-gravity technology. Reducing the number of impact categories based only on cross-correlations should be done with caution. Knowledge of the analyzed system provides further input to the choice of impact categories.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0468-3) contains supplementary material, which is available to authorized users.
Highlights
Development of more sustainable biofuel production processes is ongoing, and technology to run these processes at a high dry matter content, called high-gravity conditions, is one option
The energy input for distillation was taken from Galbe et al [42]. This figure was generated from experimental data which assumed 10 % waterinsoluble solids (WIS), while the results presented here are based on experiments run at 20 % WIS
A life cycle assessment (LCA) was performed for a high-gravity technology in development that produces ethanol from spruce wood chips
Summary
Development of more sustainable biofuel production processes is ongoing, and technology to run these processes at a high dry matter content, called high-gravity conditions, is one option. The main challenges that need to be dealt with are (a) high concentrations of inhibitory substances that are generated during the pretreatment of the feedstock, (b) high concentrations of sugars and ethanol which in themselves are inhibitory, and (c) the high viscosity of the pretreated material in the hydrolysis and fermentation step which results in mixing and mass transfer limitations. These challenges have recently been investigated for the production of ethanol from spruce wood chips [7, 8] and the results of this research form the basis of the work presented in this paper. Supporting activities Energy (steam, electricity) production, water use Foreground system Reference flow
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