Influência do Tween 80 no pré-tratamento por explosão a vapor e alcalino, hidrólise enzimática e fermentação para produção de etanol a partir da fibra de coco verde

Abstract

The green coconut fiber has been pointed out as an interesting alternative for the production of bioethanol, as Brazil is one of the largest global producers of the fruit and its disposal, generally inadequate, causes environmental problems. Pretreatments are necessary to remove compounds that protect cellulose from enzymatic attack, increasing the efficiency of enzymatic hydrolysis. The addition of non-ionic surfactants in the bioethanol production process has been studied as a strategy to increase its production and yield. Among these, Tween 80 stands out because it has a lower cost than other additives. Thus, the aim of this study was to evaluate the ethanol production from green coconut fiber using a combined steam explosion and alkaline pretreatment, comparing the simultaneous saccharification and fermentation (SSF) and semisimultaneous saccharification and fermentation (SSSF) strategies. The use of Tween 80 in the pretreatment, enzymatic hydrolysis, and fermentation steps was also investigated. Initially, the influence of the temperature and humidity parameters in the steam explosion pretreatment were evaluated on the production of glucose by enzymatic hydrolysis. The use of surfactant did not influence delignification in the steam explosion pretreatment, however it increased the conversion to glucose when compared to experiments without Tween 80. The use of surfactant in enzymatic hydrolysis increased glucose production, reaching a maximum value of 20.31 ± 0.48 g/L with combined pretreated biomass and 1.0% (w/v) Tween 80. In the absence of surfactant in any steps, the SSSF strategy stood out over the SSF. SSSF strategy showed the highest yield and ethanol production and the strain that favored the best production was Saccharomyces cerevisiae PE2. Different effects of Tween 80 were observed during fermentation. The use of 2.0% (w/v) Tween 80 reduced cell viability as well as reduced ethanol production in simulated medium, in SSF and SSSF. On the other hand, the use of 1.0% (w/v) Tween 80 increased the average ethanol production, although not enough to be statistically significant. To increase ethanol production under 30% (w/v) solids loading, SSSF variations were performed, including batch addition of biomass, batch addition of enzymes and temperature variation every 6 h. SSSF with non-isothermal batch feeding and gradual addition of enzymes stood out, reaching a maximum ethanol produced of 48.21 ± 1.13 g/L in the presence of 1.0% (w/v) Tween 80. Therefore, the results indicate that the use of the combined pretreatment generated a biomass with high cellulosic content that has a great potential for ethanol production when fermentation strategies with Tween 80 were evaluated.