Improving sweet sorghum’s bioconversion to biogas and bioethanol as an energy crop by an enhanced organosolv pretreatment was investigated. The pretreatment conducted using ethanol and isopropanol as organic solvents. First, the best pretreatment condition for isopropanol was investigated. This pretreatment were conducted at 120-160 for 30, 45, and 60 minutes with and without sulfuric acid as catalyst. Afterwards, the solvent was evaporated from the liquor and the remaining solid were washed to remove the remaining solvent. The liquid was then subjected to anaerobic digestion and the solid was dried for enzymatic hydrolysis and eventually bioethanol production. The greatest methane production was achieved from the liquor that was pretreated at 140 without catalyst for 30 min, resulting in 265.7 . The best result of ethanol production, 10.78 g/l, was achieved from the solid of the pretreatment at 140 with 1% sulfuric for 30 min. After recognizing the optimum pretreatment conditions, suitable proportion of water to alcohol was recognize through the enzymatic hydrolysis. The best results were achieved by 80% alcohol and 20% water. Then, the concentration of ethanol and isopropanol were changed and the best result was 271.24 (corresponding to 88.6% of the theoretical yield) from the liquid which was pretreated with 20% isopropanol and 60% ethanol at 140 without acid for 60 min. From remained solid, 12.3 g/l ethanol production was achieved using the pretreatment with 20% isopropanol and 60% ethanol at 140 with 1% acid for 30 min. The best result for enhanced organosolv pretreatment showed 102.1% and 128.5% increase in biogas production from the sample pretreated by 50% isopropanol and 50% ethanol 50%, respectively. Ethanol production of the pretreated solid showed 260, 120, and 104% improvement, comparing to the untreated and 50% isopropanol, and 50% ethanol pretreated substrate, respectively. In addition, the adsorption and desorption of enzymes were calculated as 163.3 mg/g substrate adsorbed protein and 88.8%, respectively. The compositional and FTIR analyses showed that the organosolv pretreatment at elevated temperatures significantly reduced the lignin and xylan contents as well as the cellulose crystallinity. Keywords : Biogas, Ethanol, Sweet sorghum, Organosolv pretreatment, Enzymatic hydrolysis.
