Otimização do processo de fermentação escura da vinhaça da cana-de-açúcar para produção de hidrogênio de baixo carbono

Abstract

Sustainable energy production has gained prominence in recent years due to the intensification of climate change resulting from the predominant use of fossil fuels. In this context, the transition toward an energy matrix composed mainly of renewable sources has increased, and among the pathways pursued for this shift, hydrogen production stands out. Hydrogen is considered a clean energy source and a promising energy carrier, especially when produced from organic residues through biotechnological processes. The present study aimed to optimize the dark fermentation process in order to maximize fermentative hydrogen production using sugarcane vinasse as the substrate and sewage sludge as the inoculum. Pretreatments were applied to enhance the activity of hydrogen-producing microorganisms and to maximize the availability of readily fermentable sugars in the reaction system. The substrate was subjected to an acid pretreatment assisted by ultrasound (pH, temperature, and sonication time), while the sewage sludge underwent an acid/thermal pretreatment followed by incubation for 24 hours (pH 3.0 and incubation at 55 °C). Both residues were characterized in terms of their physicochemical parameters. Fermentations were carried out in a 7.5 L anaerobic bioreactor, and a factorial experimental design (2³) was employed to optimize the variables pH, temperature, and substrate/inoculum volumetric ratio. Gas quantification was performed using a gas chromatograph (GC-TCD/FID) based on the chromatographic method developed and validated in this study. The results confirmed the high energy potential of vinasse, resulting from its high load of biodegradable organic matter, as well as the efficiency of the pretreatment in increasing biodegradability and sugar availability. Based on the factorial experimental design, the optimized conditions for the variables were: pH 5.5, temperature 55 °C, and substrate/inoculum volumetric ratio of 50%, resulting in a maximum hydrogen production of 1104.4 N mL H₂ L⁻¹ substrate. Through the validation assay conducted under the optimized conditions, a maximum specific hydrogen production of 1158.6 N mL H₂ L⁻¹ substrate and an accumulated hydrogen production of 3267.6 N mL H₂ L⁻¹ substrate were obtained throughout the reaction process. These results demonstrate that the integration of pretreatments and optimized operational conditions enhances the dark fermentation process and maximizes hydrogen production, indicating that the proposed route can be considered a complementary alternative to the conventional hydrogen production pathway. Keywords: Sustainability, energy transition, biohyd