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| Author(s): |
Kevy Pontes Eliodório
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Escola Politécnica (EP/BC) |
| Defense date: | 2024-03-11 |
| Examining board members: |
Thiago Olitta Basso;
Adriano Rodrigues Azzoni;
Alberto Colli Badino Junior;
Eutimio Gustavo Fernández Núñez;
Samuel Conceição de Oliveira
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| Advisor: | Thiago Olitta Basso; Reinaldo Giudici |
| Abstract | |
Brazil produces bioethanol by fermenting sugarcane juice or molasses using the yeast Saccharomyces cerevisiae. However, the process is challenging due to the extreme and stressful conditions, such as high cell density and temperature, which yeast strains face in the industrial environment. Moreover, the quality of molasses varies significantly, making the process modeling difficult. Aiming to contribute to this topic, Chapter 3 showed the development of a defined synthetic medium (2SMol) able to reproduce sugarcane substrate conditions, obtaining higher reproducibility. The effect of nutritional groups on growth parameters was conducted to achieve the final basal composition, and the significant effects of vitamins and nitrogen sources on growth parameters of S. cerevisiae strains were demonstrated. A benchmark of 2SMol results with industrial samples in industrial-like fermentations indicated that the medium can fully reproduce the physiology of yeast in sugarcane molasses. In addition, questions surrounding the effect of Maillard and caramelization reactions, which occur during sugarcane juice treatment, were investigated in Chapter 4 by assessing the growth physiology of S. cerevisiae in systems containing products of these reactions. These reactions significantly affected the specific growth rate in mineral medium and different versions of the synthetic molasses. Using the 2SMol, a mathematical model to describe the process of batch fermentations was developed and presented in Chapter 5. The phenomenological model indicated an excellent fit to experimental data in five temperatures ranging from 28 to 40°C (RSD<10%). This chapter additionally presented the initial modifications to include calorimetric features in the bioreactor. Although the experimental biological heat agreed with the theoretical, the modifications were not considered sensitive enough to measure such mild biological heat production. It is demonstrated in Chapter 6 the main differences in heat production between respiratory and fermentative metabolisms using an adequate calorimetric reactor in continuous cultivations of S. cerevisiae. The biological heat production was higher in respiratory metabolism (-1095 kJ.mol-1 glucose), in comparison with respiro-fermentative (-422) and pure fermentative at 0.1 (-157) and 0.3 (-97) h-1 dilution rates. In this chapter, it was also proposed an empirical model to describe the heat release as a function of yields, in which estimated parameter values of maintenance heat and growth heat were -0.064 and -0.152 W.g-1 biomass and -24.5 and -36.2 kJ.C-mol-1 biomass for aerobic and anaerobic conditions, respectively. Chapter 7 connects previous chapters in kinetic model validation and a model proposal to describe biological heat production. Initially, the calorimetric results of batch fermentations were assessed, in which a heat production of c.a. -480 kJ.g-1 TRS was obtained. Then, the biological heat model was proposed as a function of substrate consumption, and this model and the kinetic model proposed in Chapter 5 were validated in two sequential fed-batch fermentations simulating the ethanol industrial production in Brazil. The results of this study contribute to the knowledge about fermentation kinetics and heat production, improving reactor and temperature control designs for industrial applications. (AU) | |
| FAPESP's process: | 19/08393-8 - Experimental study and mathematical modeling of the alcoholic fermentation process considering thermal effects |
| Grantee: | Kevy Pontes Eliodório |
| Support Opportunities: | Scholarships in Brazil - Doctorate |