Environmental sustainability aspects of second generation ethanol production from sugarcane

Sugarcane-derived ethanol from Brazil has a high output to input energy ratio and high greenhouse gas savings compared to fossil fuels. Current ethanol production is based on first generation (1G) technology, which ferments the sugars extracted from sugarcane stalks. Cellulosic ethanol (2G) can be produced from what is currently considered agricultural and agro-industrial residues (straw and bagasse), and also from dedicated high biomass-producing crops. 2G ethanol provides an opportunity to intensify production, obtaining more energy per unit of area cropped and potentially reducing the environmental footprint. Straw removal from the field has more negative than positive consequences for the environment and the production system, but the effects need to be evaluated at the site and regional levels. The use of bagasse as feedstock should be evaluated using life cycle assessment methods to account for its alternative uses as raw material and in cogeneration. Energy cane, a vigorous and rustic crop selected for total biomass production rather than for sucrose, is a promising feedstock for 2G ethanol. The presence of rhizomes, a deep root system, and intensive tillering contribute to erosion control, crop longevity, and soil carbon sequestration. There is a need for more long-term experiments focusing on soil quality, nutrient cycling, greenhouse gas emissions, and crop production using innovative techniques such as stable isotope labeling andintensive soil flux measurements with automatic chambers to understand the impact of removing crop residues for bioenergy production and of using highbiomass dedicated crops. Process-based models are useful in sustainability assessments of 2G sugarcane ethanol production since they take into account site and regional variability in soil biogeochemistry, climate parameters, management practices, plant genetic traits, and the interactions of these factors. The integration of models and geographic information systems allows for regional assessments of the potential impacts of bioenergy production, contributing to the identification and promotion of sustainable pathways for cellulosic ethanol production.