Optimization of acid hydrolysis of cassava rhizome into fermentable sugars for bioethanol production using response surface methodology

Abstract

In this work, cellulose from cassava rhizome is a piquant substrate for bioethanol production because of annual renewability, large quantity, and low cost. The two-step pretreatments of cassava rhizome by using co-reagents of sodium chlorite and acetic acid followed with sodium hydroxide were performed in the removal of both lignin and hemicellulose for cellulose preparation. After pretreatment, cellulose content was increased to 70.5%, whereas hemicellulose and lignin were reduced to 11.2% and 9.4%, respectively. In the optimization of acid hydrolysis, a Response Surface Methodology (RSM) was applied to evaluate the relationship of various parameters could give the best experimental results. Additionally, a Central Composite Design (CCD) was utilized to plan the run experiments. Afterward, hydrolysis of pretreated cassava rhizome was conducted under optimal conditions; at 1210C, 15 psi, 90 min. of hydrolysis time, 22.56 ml of acid volume per gram of sample, and 0.20 M of acid concentration. This process produced glucose with yield up to 81.25%. On the contrary, low content of inhibitors (5-hydroxymethyl furfural and furfural) were measured. The hydrolyzate was fermented by Saccharomyces cerevisiae TISTR 5339 gave both ethanol concentration and ethanol with yield up to 10.42 g/l and 23.51 g/100 g substrate, respectively. When compared with other agricultural residues, the production of ethanol from cassava rhizome in this work was higher. Therefore, cassava rhizome is a possible new source of feedstock for the production of bioethanol in the ethanol industry.