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.T. Forster-Carneiro acknowledges the database support and samples of materials from NIPE/NIEPE-UNICAMP/UFMT, process numbers 91.752/01-P-17839-2019 and 91759/01-P-18069/2019. T. Forster-Carneiro acknowledges the financial support from the Sao Paulo Research Foundation - FAPESP (2018/05999-0; 2018/14938-4) , and CNPq for the productivity grant (302473/2019-0) . L.S. Buller ac-knowledges the financial support from FAPESP (2020/10323-5) . W.G. Sganzerla acknowledges the financial support from FAPESP (2019/26925-7) . M. Tena acknowledges the Spanish Ministry of Economy, Industry, and Competitiveness for her pre-doctoral contract (Call 2016)