Multi-objective optimization of the first and second-generation ethanol supply chain in Brazil using the water-energy-food-land nexus approach

Biofuels are essential in achieving some of the United Nations' Sustainable Development Goals (SDGs) by integrating water consumption, energy and food production, and land usage. The water-energy-food-land Nexus approach (WEFL Nexus) supports integrated production planning of natural resources and promotes sustainability. In Brazil, sugarcane ethanol production is considered one of the biofuel nation's solutions to reduce dependence on fossil fuels. Ethanol production constitutes a renewable and sustainable energy source. This research analyzes the efficiency and sustainability of the Brazilian ethanol supply chain, comparing a conventional scenario focusing only on economic efficiency (restricted to first-generation ethanol production) with another scenario considering WEFL Nexus objectives (and first and second-generation ethanol production). The study developed a multi-objective mathematical model to analyze the supply chain efficiency, combined with a multi-criteria decision approach analysis. The results indicate a gain in efficiency and sustainability with the second-generation manufacturing plants. In the Nexus scenario, supply chain efficiency increased due to the 35.63 % additional production of second-generation ethanol and the 2.94 % manufacturing cost minimization. Also, the Nexus scenario met sustainable and social demands that were not fulfilled by the non-Nexus scenario. An AHP model investigated the adequacy of the mathematical results and confirmed that the Nexus scenario was the most suitable solution for the Brazilian supply chain, with 63 % of the stakeholder's preferences. Results indicated that the Nexus approach is essential for achieving the long-term SDGs.