Current developments and challenges of green technologies for the valorization of liquid, solid, and gaseous wastes from sugarcane ethanol production

Highlights: • Wastes from sugarcane processing and classic reuse technologies are discussed. • Vinasse, CO_2, and fermentation yeast are underutilized wastes. • Emerging green technologies for value-added reuse of hazardous wastes are presented. • Anaerobic digestion and CO₂ reuse are key technologies in a biorefinery context. • Future biorefineries will likely produce bioenergy, fertilizers, and biochemicals. The sugarcane industry is one of the largest in the world and processes huge volumes of biomass, especially for ethanol and sugar production. These processes also generate several environmentally harmful solid, liquid, and gaseous wastes. Part of these wastes is reused, but with low-added value technologies, while a large unused fraction continues to impact the environment. In this review, the classic waste reuse routes are outlined, and promising green and circular technologies that can positively impact this sector are discussed. To remain competitive and reduce its environmental impact, the sugarcane industry must embrace technologies for bagasse fractionation and pyrolysis, microalgae cultivation for both CO₂ recovery and vinasse treatment, CO₂ chemical fixation, energy generation through the anaerobic digestion of vinasse, and genetically improved fermentation yeast strains. Considering the technological maturity, the anaerobic digestion of vinasse emerges as an important solution in the short term. However, the greatest environmental opportunity is to use the pure CO₂ from fermentation. The other opportunities still require continued research to reach technological maturity. Intensifying the processes, the exploration of driving-change technologies, and the integration of wastes through biorefinery processes can lead to a more sustainable sugarcane processing industry.