Emergy Assessment of Ethanol Production From Sugarcane in Brazil

The present study assesses the environmental sustainability, or the ecosystem support, of ethanol produced from sugarcane and examines the environmental feasibility of a large-scale production through the use of: emergy methodology. The study includes agricultural and industrial stages, as well the sugarcane transport, and was accomplished for two scenarios: a) only the directly consumed resources were accounted; b) including negative externalities associated to the production system, such as global warming contribution, loss of native forest and intoxication by pesticide. The following indicators were obtained for ethanol: Transformity: 4.87E+05 seJ/J; Renewability: 30.9%; Emergy yield ratio: 1.57; Environmental loading ratio: 2.23; Sustainability Index: 0.71. The Renewability of ethanol is very low and the emergy indices indicate important environmental stress and resources consumption. Results for ethanol production considering negative externalities were: Transformity: 5.87E+05 seJ/J; Renewability: 25.7%; Emergy yield ratio: 1.43; Environmental loading ratio: 2.90; Sustainability Index: 0.50. Externalities accounted for 20% of total emergy input for the agricultural stage. These results evidence the importance of accounting for the externalities to evaluate the system’s performance and, therefore, they should be included when assessing biofuels sustainability. Besides, they indicate that large scale ethanol production present low sustainability. The adoption of alternative production systems, such as agroecological models, could improve its environmental impacts and should be evaluated to allow the design of new models able to deliver more renewable energy with less environmental and social impacts.