An investigation on the environmental impacts and energy efficiency of biogas and bioethanol production from sugarcane and sugar beet molasses: A case study

This study presents a comparison in terms of both environmental effect/energy efficiency of different designs of the process for sugarcane/sugar beet molasses-based bioethanol. In the present work, two scenarios were designed/compared, including the production of sugarcane-based (Scenario 1) and sugar beet molasses bioethanol (Scenario 2) in Khuzestan Province as an agricultural hub of Iran. Furthermore, an improved process, including a biogas production line from the residual vinasse from the distillation of molasses for bioethanol obtaining is presented, both from sugarcane (scenario 3) and sugar beet (scenario 4), and life cycle assessment (LCA) method was employed for determination of environmental impacts. The results, in terms of net energy value (NEV), i.e. the difference between the energy content of ethanol and the energy used in its production and distribution, were very similar as 11.03 MJ and 11.15 MJ, respectively. Nevertheless, the results of the environmental impact analysis indicated that bioethanol production from sugarcane molasses had a higher impact compared to the sugar beet in terms of global warming potential, fossil, and metal depletion, particulate matter formation, human toxicity, and climate change ecosystems. Furthermore, the addition of the biogas production plant from the residual vinasse (scenarios 3 and 4) resulted in a considerable reduction of all studied environmental impacts (i.e., climate change, human toxicity, ozone depletion, photochemical oxidant formation, terrestrial acidification, freshwater ecotoxicity, marine ecotoxicity, ionizing radiation, fossil depletion, and global warming). As an example, by applying scenarios 3 and 4, the global warming potential for sugarcane and sugar beet was reduced by 61.2% and 83%, and the climate change decreased by 61% and 81% for bioethanol production from sugarcane and sugar beet, respectively.