Produção de biobutanol por fermentação acetona-butanol-etanol (ABE) utilizando Clostridium beijerinckii ATCC 10132 a partir do hidrolisado enzimático da casca de coco verde

Abstract

The search for renewable energies that minimize the environmental damage caused mainly by the burning of fossil fuels has encouraged studies for the diversification of the global energy matrix. In the case of Brazil, the insertion of new biofuels such as butanol associated with the valorization of lignocellulosic biomass presents an opportunity to consolidate its historical vocation in the leadership of renewable energy sources. Green coconut husk (GCS) is an abundant agro-industrial waste that can be converted into value-added products while solving environmental problems caused by its inappropriate disposal. In this context, the potential of the GCS was investigated in the production of cellulosic butanol (or biobutanol) by ABE (Acetone-Butanol-Ethanol) fermentation, using Clostridium beijerinckii. Initially, enzymatic hydrolysis tests were carried out to evaluate the release of sugars and the ability to recycle commercial cellulolytic cocktails. The behaviour and recovery of cellulolytic enzymes remaining from pre-treated GCS (by dilute acid, alkali, and acid-alkali) were evaluated. Additionally, batch fermentation tests were performed to investigate the influence of some nutrients (nitrogen sources and mineral medium) as supplements on the hydrolysate to produce butanol and other solvents. Fed batch fermentation was performed in order to improve butanol's yield and productivity. Adsorption studies from cellulases showed that pre-treated GCS by alkali ensure large amount of free cells (52% for Trichoderma reesei cocktail and 69% for Cellic CTEC2 cocktail) and greater susceptibility of desorption with buffer (~50%). Sugar yields greater than 60% were obtained using recycled enzymes from solid and liquid fractions. Recycling enzymes by two cycles hardly affected the catalytic capacity in the pre-treated GCS hydrolysis by alkali, and acid-alkali. Using hydrolysate with 9 g/L of sugars (glucose + xylose), the fermentation ABE reached a yield of 0.53 g/g after 96 h, in which 3.4 g/L of butanol were obtained. The absence or insufficiency of some nutrients (minerals and phosphate buffer) resulted in low yield of ABE products, indicating the relevance of the adequacy of supplements to the chosen fermentation medium, and the type of microorganism used. Fed batch increased productivity in ABE fermentation (0.08 g/L.h butanol). The results indicate that green coconut waste has potential to contribute to the energy sector and is a low-cost raw material for the biotechnological production of butanol, as an alternative and renewable product