Effect of ultrasonication of Switchgrass on fermentable sugar production and biomass physical structure

Abstract

Pretreatment of lignocellulosic biomass for enhancing sugar yields has been studied extensively over the years.  Conventional methods employed to preprocess biomass to make it conducive for enzymatic hydrolysis have been hampered by issues like poor energy efficiency and production of undesirable by-products.  Ultrasonication, which involves the treatment of biomass through ultrasonic sound waves in a liquid medium without additional chemicals, is believed to have potential for biomass pretreatment.  In this study the effects of ultrasonication on switchgrass, a potential feedstock for bioethanol production due to its high cellulosic content, were investigated.  Results of compositional analysis and scanning electron microscopy conducted to visualize structural disintegration in sonicated samples were used to select pretreated samples for enzymatic hydrolysis at different enzyme loadings.  Temperature controlled ultrasonication for 60 min at 100% amplitude in a stainless steel vessel, resulted in the highest carbohydrate conversions of 84.6% and 84.7% with Cellic® CTec2 and Alternafuel 200 L at 0.3 g enzyme protein g^-1 dry biomass, respectively.  However ultrasonication did not significantly impact composition of switchgrass and subsequent hydrolysis of untreated and treated samples was not significantly different.  Based on the overall results, it is inferred that although ultrasonication alone did not provide enhanced sugar generation from switchgrass, its tendency to disrupt biomass structure could be utilized for preliminary size reduction steps and performance could be improved by further investigation of frequencies, amplitudes, enzyme loadings and process operation parameters.

Keywords: Panicum virgatum, amplitude, pretreatment, hydrolysis, scanning electron microscopy