Bioenergy production from sweet sorghum stalks via a biorefinery perspective
Besides free sugars, sweet sorghum stalks contain cellulose and hemicellulose that can be used for biofuel production. The pretreatment of stalks without the extraction of free sugars is more complicated than typical lignocelluloses, because of the degradation of free sugars during most pretreatment processes. In this study, the bioconversion of sweet sorghum stalks into biogas and bioethanol was studied using an improved organosolv pretreatment within a biorefinery framework. The organosolv pretreatment was developed using an aqueous solution of ethanol (EtOH) and isopropanol (IPOH). The process was optimized to obtain a liquor containing free sugars with the least sugar degradations together with a highly degradable solid fraction. The liquor was subjected to anaerobic digestion for biomethane production, while the solid was used for ethanol production via simultaneous saccharification and fermentation (SSF). The most influencing pretreatment parameters, i.e., temperature, time, alcohol to water ratio, EtOH to IPOH ratio, and the presence or absence of sulfuric acid (as a catalyst), were adjusted to achieve the highest yields of bioconversion. The maximum methane and ethanol production yields of 271.2 mL CH4/g VS and 87.8% (equal to the gasoline equivalent of 0.170 and 0.241 L/kg, respectively) were achieved from the liquor and pretreated solid, respectively; however, they were obtained at different optimum conditions. Considering the biorefinery perspective, the highest gasoline equivalent of 0.249 L/kg was efficiently obtained from the whole process after pretreatment at 140 °C for 30 min using 60:20 EtOH/IPOH ratio in the presence of 1% sulfuric acid. Further analyses, including enzymatic adsorption/desorption, compositional analysis, FTIR, and SEM, were conducted to investigate the effects of this newly developed pretreatment on the substrate.
KeywordsBiogas Ethanol Sweet sorghum stalk Organosolv pretreatment Enzymatic hydrolysis
The authors are grateful to Dr. Abbas Almodares (Department of Biological Science, University of Isfahan, Iran) for providing the sweet sorghum stalks and Novozymes, Denmark, for providing Cellic® HTec2 and Cellic® CTec2 enzymes for this study.
This study was supported by the Research Institute for Biotechnology and Bioengineering, Isfahan University of Technology, and Iran National Science Foundation (INSF, Grant No. 95003713).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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