Bioethanol from Fresh and Dried Banana Plant Pseudostem

Abstract

Lignocellulosic wastes have stood out in the study and development of processes aimed at producing biofuels. Brazil is one of the world’s largest food producers and ranks fifth in world production of bananas with an average production of seven million tons per year. For each ton of bananas harvested, around four tons of lignocellulosic wastes are generated, among which 75% consists of banana plant pseudostem. This work investigated the production of bioethanol by Saccharomyces cerevisae using this residue (pseudosteam) as a fermentation substrate previously hydrolyzed under the following conditions: (a) 250 g/L of fresh biomass (equivalent to 11.75 g/L of dry matter) cut into about 1 mm long pieces and (b) 70 g/L of dry and milled biomass (drying in 60 ºC forced air draft tray dryer and milling in Solab knife mill until particles of size smaller than 30 mesh). The biomass pre-treatments with H₂SO₄ 2% m/m and NaOH 3% m/m, both conducted at 120 °C, 15 min were evaluated. For saccharification of the pre-treated biomass, enzymatic hydrolysis (24 h, pH 5.5, 45 °C) using Novozymes® enzymatic complex composed of cellulase, beta-glucosidase and xylanase was used. The experiments were conducted in Erlenmeyer flasks containing 100 mL of work volume. The greatest percent yield in glucose (Y_RS = 79.5±4.4 %), calculated based on the theoretical yield of cellulose hydrolysis to glucose (1.1 g/g), was obtained with fresh biomass pre-treated with NaOH. This value was 84% higher than the percent yield resulting from the pretreatment of 70 g/L of dry biomass with the same type of hydrolysis catalyst (Y_RS = 43.2±1.2 %) and 31% higher than the value reached in the pretreatment of this same biomass with H₂SO₄ (Y_RS = 60.7±6.7%). The maximum RS value in hydrolyzed liquor (without prior concentration by evaporation) was obtained from dry biomass saccharification with H₂SO₄ (26.6±1.1 g/L). The fermentation of this liquor, after concentrating to RS = 62.1 g/L, resulted in an ethanol production of 22.1±0.8 g/L with respective values of Y_P/RS = 0.47±0.03 g/g, ethanol productivity (Q_P) 1.83±0.12 g/L.h and effectiveness of alcoholic fermentation (E_P) 80.4±0.12 %.