Urvi D. Kothari, Sandeep Kumar, Ram B. Gupta, and Y.Y. Lee. Department of Chemical Engineering, Auburn University, 212 Ross Hall, Auburn University, Auburn, AL 36849-5127
Switchgrass was treated hydrothermally at 150-190ºC and 500-2000 psi. This pretreatment is advantageous in that hydrothermal media are non-toxic, environmentally benign, and inexpensive. In a second pretreatment scheme, a small amount of K2CO3 was added during the hydrothermal pretreatment. Both treatment schemes give glucan yields of above 70% when treated at temperatures in the range of 150-190ºC. At higher temperatures, digestibility in the vicinity of 90% was obtained. Addition of K2CO3 promotes conservation of carbohydrates, including hemicelluloses. Since the cellulase enzyme used in this study (Spezyme CP) has relatively low hemicellulase activity, it was supplemented with hemicellulase enzymes. In this study, the effect of different enzyme formulations on enzymatic digestibility was investigated. Applying various combinations of Spezyme CP, beta-glucosidase and hemicellulase enzymes, the optimum enzyme formulation which maximizes glucan as well as xylan yields, was determined. For the two different pretreatment schemes studied (with and without alkali), the effect of enzyme supplementation was different. Xylanase addition showed higher effect on the sample treated with the alkali-assisted hydrothermal pretreatment. Residual free lignin in the pretreated substrate is known to have a negative effect on the enzymatic hydrolysis. As a means to alleviate this problem, a surfactant (Tween 80) was added during the enzymatic hydrolysis experiments. The results are analyzed to understand the effect of surfactant on the final sugar yields for both pretreatment schemes.
