The exergy efficiency of producing microalgae biodiesel using stillage from ethanol fermentation as a cultivation medium was assessed in this work. Thus, mass and energy balances considered the following subsystems of a sugarcane ethanol mill: ethanol and CO2 production from sugarcane juice; biomethane production generated by anaerobic digestion of stillage; microalgae cultivation; conversion of lipids into biodiesel, and cogeneration via sugarcane bagasse and straw. The process integration strategy includes the CO2 utilization produced during ethanol fermentation for the photoautotrophic growth of microalgae; the biodigested stillage as the medium for the heterotrophic growth of microalgae; the burning of biomethane in the cogeneration unit, and the use of electricity and steam cogenerated in the sugarcane mill in the microalgae-biodiesel plant. The microalgae production and conversion plant achieved an exergy efficiency of 29 % with an exergy destruction rate of 159 MW. After process integration, the overall exergy efficiency was 39 % with an exergy destruction rate of 838 MW. This technical performance could represent an indicator following the circular economy concept to increase the profitability of the sugar and ethanol industry. Hence, the issue associated with the stillage disposal (treatment or utilization) from sugarcane ethanol production was addressed from the exergy analysis perspective to explore the potential of this wastewater inherent to the bioenergy sector.