Bioethanol from corn stover - Integrated environmental impacts of alternative biotechnologies

The environmental impact potentials of producing bioethanol from corn stover were systematically assessed by life cycle assessment using datasets reported in the literature. The 15% best datasets with respect to global warming potential for seven different technological configurations were extracted from a published database reviewing 474 publications on converting corn stover to bioethanol. A total of 10 impact categories were evaluated. The impacts included both environmental loads and savings, and generally ranged from -0.1 to 0.1 person-equivalent per ton of dry corn stover for most non-toxic impacts and -0.2 to 0.5 person-equivalent for toxic impacts. Fossil fuel substitution with bioethanol provided savings in most impact categories, and so did the energy recovered from the residues, while enzyme production was a significant load. The treatment and discharge of effluent from the liquid residues may constitute a significant load to the environment. Based on the cumulative probabilities of overall environmental performance together with the bioethanol amount produced, the prioritisation of technologies for further development should be as follows: steam explosion (S4) and ammonia-based (S6) technologies as the highest priorities with approximately 100% and 40% probabilities to have savings in non-toxic and toxic impacts, respectively; acid (S1), alkaline (S2) and fungi (S7) technologies as medium priorities and solvent-based (S3) and liquid hot water (S5) technologies have the lowest priorities. We suggest the integration of life cycle assessment modelling to the research and development of biofuel production from biomass waste to ensure that the technologies being developed for full-scale applications are sustainable.