Optimization of Organosolv pretreatment conditions and hydrolysis by Bacillus sp. BMP01 for effective depolymerization of wheat straw biomass

Abstract

The main objective of this study is to enhance the depolymerization of wheat straw biomass into its major constituents by optimizing Organosolv pretreatment conditions based on central composite design (CCD). Exposure time from 20 to 40 min, pretreatment temperature from 70 to 90 °C, and acid concentration from 60 to 80%, v/v were considered. An equal amount of formic acid and acetic acid was used in the Organosolv pretreatment to constitute the required acid concentration. In the various experiment performed, about 31.2–74.64% of cellulose were released, 62.42–71.29% of total lignin were solubilized, and 9.85–13.87% of hemicellulose were preserved in the biomass after Organosolv pretreatment. Optimum pretreatment condition was achieved at 79.5 °C, 69.5% acid concentration, and exposure time of 28.80 min. After pretreatment at this condition, the final composition of the biomass was found as follows: 74.13% cellulose, 13.54% hemicellulose (67.26% of initial hemicellulose was preserved), and 5.55 lignin (69.42% of total lignin removed). Analysis of variance (ANOVA) method was used to test the significance of the model as well as the adequacy and fitness of the experimental data into the models. It was noticeable that the exposure time, pretreatment temperature, and acid concentration influenced the pretreatment process. About 70.22% of conversion efficiency (684 mg/g) was achieved after the 10th day hydrolysis of optimally pretreated wheat straw biomass by Bacillus sp. BMP01. Ethanol yield of 40.85% was obtained by fermentation of the hydrolyzed straw. The pretreatment process significantly reduced hemicellulose solubilization that enhanced the yield of reducing sugars. The study demonstrated the possible combination of optimal Organosolv pretreatment conditions along with the microbial hydrolysis for bioethanol production from wheat straw and with possible extension to other agricultural residues. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.