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

Abstract

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.