Estudo da produção de etanol a partir do bagaço de laranja em biorreator de coluna de bolas com Saccharomyces cerevisiae imobilizadas em alginato de cálcio

Abstract

The production of renewable biofuel is an alternative to reduce the amount of lignocellulosic waste generated during the processing of fruits in industries. However, it is still a challenge to define an economically viable process, in view of other alternatives, such as targeting animal feed., In this context, this work aims to study ethanol production from orange bagasse hydrolyzate with immobilized Saccharomyces cerevisiae cells in sodium alginate gel. The experiments were carried out using citrus residues from the orange juice processing industry, first crushing and drying were carried out, then the hydrothermal pre-treatment was carried out, and waste characterization was carried out. Then, acidic and enzymatic hydrolysis was performed. Hydrolysis with sulfuric acid diluted to 1% (m v -1 ), 120 ° ₢ for 30 minutes. Enzymatic hydrolysis with commercial enzymes (Celluclast 1.5 L), to evaluate the best conditions to obtain fermentable sugars, by the analysis of determination of total reducing sugars (ART). The study was carried out by means of a central rotational composite design (DCCR), analyzing the concentration factors of cellulase enzymes (8 to 15 FPU mL-1 ) and pectinases (4 to 10 U mL-1 ) and the time (2 to 24 hours) The fermentation process tests with the yeast Saccharomyces cerevisiae G2-104 immobilized in 3% sodium alginate (m v -1 ), the orange pomace hydrolyzate as substrate, was conducted in a bubble column bioreactor at 30 ° C with aeration of 2 vvm for 48 hours. The four repeated batches were carried out each lasting 24 hours. Analyzing the results, the characterization of industrialized wastes in natura was 18.8% cellulose, 10.7% hemicellulose, 3.14% lignin and 15.1% pectin, and after hydrothermal pre-treatment 19.52% cellulose, 7.41% hemicellulose, 1.33% lignin. The most significant factor in the experimental design analyzed was time, and the optimized condition for maximum sugar concentration was found in 12.5 FPU mL1 of cellulase, 4.4 U mL-1 pectinase and 37.4 hours of hydrolysis resulting in 21.06 g.L -1 of ART. The results obtained for the simple batch with immobilized S. cerevisiae G2-104 cells was 2.33 g L -1 of ethanol for the test (FHE-2) and 2.57 g.L -1 of ethanol for the test (FSHE-2) in 12 hours of cultivation. For repeated batch fermentation with immobilized S. cerevisiae G2-104 cells, a maximum ethanol concentration of 4.95 g L -1 was obtained in the second batch. The highest volumetric productivity of ethanol (Qp) in repeated batches was obtained in batches 3 and 4 (0.77 and 0.78 g L -1 h -1 ) and the highest ethanol yield factor per substrate consumed (Yp/s) was in batch 1 (5.27 g g -1 ). The immobilized cells showed good fermentative activity for long periods, allowing their reuse during the four batches without breaking the alginate spheres, demonstrating the good use of this support for ethanol production.