Wednesday, May 2, 2007 - 9:40 AM

Enhancement of enzymatic digestibility of switch grass by dielectric heating pretreatment

Zhiyou Wen, Biological Systems Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 and Yifen Wang, Biosystems Engineering, Auburn University, Auburn, AL 36849.

A dielectric heating based technology was used for treating cellulosic materials to enhance the enzymatic digestibility of those materials.  Our hypothesis is that the dielectric heating can selectively heat the more polar (lossy) part and creates a “hot spot” within the inhomogeneous cellulosic materials, which results in an “explosion” effect among the treated materials.  Those unique features (i.e., short heating time, volumetric heat transfer, inhomogeneous distribution of dielectric energy within the sample, and selective heating on lossy compounds) can improve breaking-down of the recalcitrant structures of cellulosic materials.   

In this work, switch grass was used as the cellulosic material and dielectric heating was chose at microwave frequency.  It was found that enzymatic digestibility of dielectric heating-pretreated switch grass was enhanced 61% compared to that of conventional-heating pretreated materials.  The practice of presoaking the switch grass with alkali further enhanced the pretreatment efficiency.  Scanning electron microscope (SEM) image of the materials showed that samples treated by dielectric heating and by dielectric heating/alkali resulted in a delignified and more enzyme-accessible material.  The following enzymatic hydrolysis of those materials indicated that dielectric pretreatment greatly increased the sugar yield over the conventional processes.  The optimal pretreatment conditions were determined as 0.1 g NaOH/g dry matter of alkali loading, 100g dry biomass/L of solid loading with 30 min treatment time.  At this condition, the yield of total sugars (glucose and xylose) released from the pretreatment and hydrolysis processes was 99% of the maximum sugar potential yield.