Potential Cassava Peel Waste (Manihot esculenta Crantz) in The Production of Bioethanol by Enzymatic Hydrolysis and Fermentation Using Zymomonas mobilis Bacteria

Abstract

Cassava is one of the most widely produced agricultural products in Indonesia with cassava peel waste of 20%. Cassava peel contains carbohydrates and stores a high cellulose content so that it has a potential to be a bioethanol. This study aims to utilize cassava peel waste for bioethanol production with an alkaline pretreatment process, cellulase enzyme hydrolysis and fermentation by using Zymomonas mobilis bacteria. Alkaline pretreatment with 14% NaOH is used to hydrolyze lignocellulose. The hydrolysis optimization process enzymatically applies the Surface Response Method (RSM) to determine the optimum conditions at hydrolysis pH in the range of 2-10 and hydrolysis temperature in the range of 30-70 °C by analyzing glucose levels using the Dinitrosalicylic Acid (DNS) method and UVvis spectrophotometry instruments. Surface Response Method (RSM) is likewise implemented to decide the greatest conditions of the fermentation process. The pH measurement ranges 2-10, and fermentation time takes 6 to 168 hours. Based on the results of research, it results a lignin content of 6.68% (b/b), cellulose content of 58.4% (b/b), and hemicellulose content of 27.3% (b/b). The optimum conditions of the hydrolysis process obtained an optimum glucose level of 9.22mg/mL at pH 2 and a hydrolysis temperature of 50°C. The optimum conditions of the fermentation process use Zymomonas mobilis at pH 6 while fermentation time takes 168 hours analyzed using a refractometer produced a bioethanol content of 37.75% (v/v) and a gas chromatography produced a bioethanol content of 54.94% (v/v).