Microwave-Based Alkali Pretreatment of Switchgrass and Coastal Bermudagrass for Bioethanol Production

Switch grass and coastal bermuda grass are promising lignocellulosic feedstocks for bioethanol production. However, pretreatment of lignocelluloses is required to improve production of fermentable sugars from enzymatic hydrolysis. Microwave-based alkali pretreatment of switch grass and coastal bermuda grass was investigated in this study. Pretreatments were carried out by immersing the biomass in dilute alkali reagents and exposing the slurry to microwave radiation at 250 W for residence times ranging from 5 to 20 min. Simons' stain method was used to quantify changes in biomass porosity as a result of the pretreatment. Pretreatments were evaluated based on yields of total reducing sugars, glucose, and xylose. An evaluation of different alkalis identified sodium hydroxide as the most effective alkali reagent for microwave-based pretreatment of switch grass and coastal bermuda grass. 82% glucose and 63% xylose yields were achieved for switchgrass and 87% glucose and 59% xylose yields were achieved for coastal bermuda grass following enzymatic hydrolysis of biomass pretreated under optimal conditions. Dielectric properties for dilute sodium, hydroxide solutions were measured and compared with solid losses, lignin reduction, and reducing sugar levels in hydrolyzates. Results indicate that dielectric loss tangent of alkali solutions is a potential indicator of the severity of microwave-based pretreatments. (C) 2009 American Institute of Chemical Engineers Biotechnol. Prog., 26: 644-652, 2010