Techno-economic evaluation of bioenergy production from anaerobic digestion of by-products from ethanol flex plants

Ethanol production implies in by-products generation, mainly vinasse and stillage, respectively generated from sugarcane and corn ethanol production in flex plants. Both by-products require efficient treatment routes to avoid environmental side-effects to support energy recovery. Accordingly, the aim of this study was to evaluate the techno-economic potential of bioenergy (electric and thermal energy) production from the anaerobic digestion (AD) of vinasse and stillage. Three scenarios were defined: (a) Scenario 1, AD of vinasse; (b) Scenario 2, AD of stillage; and (c) Scenario 3, AD of vinasse and stillage in an integrated process. From the results, the methane production was estimated at 3.8 x 106 m3 year-1 considering the AD of stillage and vinasse in Scenario 3. The electricity and thermal energy generation was estimated as 14.61 GWh year-1 and 1.37 x 105 GJ year-1, respectively. This energy would mitigate 1096.05 and 7659.27 ton CO2eq year-1 when replacing fossil fuel energy. The profitability analysis indicated a positive net present value in the scenarios evaluated, however, the highest value was achieved for Scenario 3 (7,890,407.44 USD). For the integrated process, an internal return rate of 86.87% and a payback of 0.68 year were observed. The sensitivity analysis showed that the project profitability is highly dependent on electricity and thermal energy selling prices. In conclusion, AD demonstrated to be a feasible alternative for vinasse and stillage management in an integrated process, being a sustainable technology to the circular economy transition and energy matrix decarbonization.

Automated summary

This study evaluated the techno-economic potential of bioenergy production from the anaerobic digestion of vinasse and stillage, showing that methane, electricity, and thermal energy could be generated in Scenario 3. The energy output could mitigate CO2 emissions and the profitability analysis indicated positive results, especially for the integrated process.