Potential of agricultural residues and hay for bioethanol production

Production of bioethanol from agricultural residues and hays ( wheat, barley, and triticale straws, and barley, triticale, pearl millet, and sweet sorghum hays) through a series of chemical pretreatment, enzymatic hydrolysis, and fermentation processes was investigated in this study. Composition analysis suggested that the agricultural straws and hays studied contained approximately 28.62 - 38.58% glucan, 11.19 - 20.78% xylan, and 22.01 - 27.57% lignin, making them good candidates for bioethanol production. Chemical pretreatment with sulfuric acid or sodium hydroxide at concentrations of 0.5, 1.0, and 2.0% indicated that concentration and treatment agent play a significant role during pretreatment. After 2.0% sulfuric acid pretreatment at 121 degrees C/ 15 psi for 60 min, 78.10 - 81.27% of the xylan in untreated feedstocks was solubilized, while 75.09 - 84.52% of the lignin was reduced after 2.0% sodium hydroxide pretreatment under similar conditions. Enzymatic hydrolysis of chemically pretreated ( 2.0% NaOH or H2SO4) solids with Celluclast 1.5 L - Novozym 188 (cellobiase) enzyme combination resulted in equal or higher glucan and xylan conversion than with Spezyme (R) CP-xylanase combination. The glucan and xylan conversions during hydrolysis with Celluclast 1.5 L - cellobiase at 40 FPU/g glucan were 78.09 to 100.36% and 74.03 to 84.89%, respectively. Increasing the enzyme loading from 40 to 60 FPU/g glucan did not significantly increase sugar yield. The ethanol yield after fermentation of the hydrolyzate from different feedstocks with Saccharomyces cerevisiae ranged from 0.27 to 0.34 g/g glucose or 52.00 - 65.82% of the theoretical maximum ethanol yield.