Banana rachis as a potential source of second generation ethanol

The process necessary to obtain second-generation bioethanol from the banana rachis involves three steps: 1. Pretreatment to delignify the dry banana rachis. 2. Hydrolysis of the delignified sample to obtain fermentable sugars from the acid and enzymatic degradation of cellulose and hemicellulose. 3. Fermentation of glucose and pentoses. The delignification of banana rachis has been tested with three oxidizing methods; with electrochemically activated oxidizing solution (ECA), with 2% alkaline hydrogen peroxide solution and with 5% sodium hypochlorite. Alternatively, delignification with organosolv has been tried. The results of the delignification according to the Tappi method indicate that there is no significant improvement when using organosolv compared to the oxidizing methods. The result of the delignification with oxidizing methods denotes that the greatest effect for lignin removal occurs with the 5% sodium hypochlorite solution for 30 minutes, in the ratio 4g rachis / L oxidant solution. There are no significant differences in the final lignin content when using ECA solution (4 g rachis / L) or alkaline hydrogen peroxide solution (16 g rachis / L). The results of the hydrolysis indicate that the lignocellulosic matrix of the banana rachis is particularly resistant to the action of diluted mineral acids, while it is very sensitive to degradation by the effect of concentrated mineral acids, so the production of fermentable sugars is not significant under the usual reaction conditions. The use of organic acids, characterized by behaving as weak acids represents an interesting alternative for traditional hydrolysis methods by significantly increasing the concentration of glucose and other fermentable sugars. A treatment with maleic acid solution (2% W/V), increase of up to 20% of glucose compared to the process with sulfuric acid (20% W/V). The combined treatment of enzymatic and acid hydrolysis between maleic acid with B-glucanase was produced a yield of 60%; the hydrolysis enzymes produces an increase of up to 24% of glucose with respect to single enzymatic hydrolysis. The results of the fermentation indicate that the average yield for obtaining second generation ethanol is 0.16 g / g of banana rachis. The amount indicates that it is approximately half of that obtained from other agro industrial waste and residues, mainly those coming from the processing of wheat straw and other herbaceous materials. For Ecuador, the potential production of ethanol by this method amounts to 15 million liters per year, which can be an interesting opportunity for farmers in the productive areas. The proposed process that starts from the use of banana rachis treated with 2% (W/V) alkaline hydrogen peroxide with 0.5% NaOH (W/V) for the corresponding delignification, 2% maleic acid (W/V) and cellulases from Aspergillus niger in the subsequent stages of hydrolysis to obtain glucose and the final stage of fermentation with Saccharomyces cerevisiae represents a valid alternative for obtaining second generation ethanol.