Life cycle assessment of bioethanol production from cattle manure

Biofuels can contribute significantly to reducing environmental damage. Lignocellulosic bioethanol can be an alternative to fossil fuels and is of great strategic importance to Brazil. In this context, the life cycle assessment (LCA) of bioethanol production from cattle manure (CM) was studied. CM is a biomass rich in cellulose that can be converted to glucose and other fermentable sugars. In the LCA, 1000 kg of CM were used as a functional unit of processing. The ReCiPe method and the EcoInvent libraries were used in SimaPro software version 7.3.2. We considered the following categories of impact: climate change, ozone depletion, terrestrial acidification, freshwater eutrophication, marine eutrophication, human toxicity, photochemical oxidant formation, particulate matter formation, terrestrial ecotoxicity, freshwater ecotoxicity, marine ecotoxicity, ionizing radiation, agricultural land occupation, urban land occupation, natural land transformation, water depletion, mineral resource depletion and fossil resource depletion. The categories damaged were human health, ecosystems and natural resources. The results obtained in the life cycle impact assessment (LCIA) and the proposed changes in the process contributed to the reduction of environmental impacts. The inputs/outputs that made the greatest contribution to environmental impacts were energy consumption, drying emissions, sulfuric acid in the pretreatment, buffer in the enzymatic hydrolysis and sodium phosphate in the fermentation. Bioethanol production from CM has a low impact on most of the categories and is a process that can be improved to reduce its impact mainly by changing the energy type. In the LCIA, it was observed that the CM bioethanol production eliminates the need for disposal treatment of the manure and uses residual raw material in a biofuel production, thus counterbalancing the environmental impacts of the bioethanol process.