Acceleration of the Enzymatic Hydrolysis of Corn Stover and Sugar Cane Bagasse Celluloses by Low Intensity Uniform Ultrasound

The cost-competitive production of bio-ethanol and other biofuels is currently impeded, mostly by the high cost and the low efficiency of enzymatic hydrolysis of feedstock biomass and especially plant celluloses. Despite substantial reduction in the cost of production of cellulolytic enzymes in recent times, the conversion of plant cellulose into sugars still remains an expensive and slow step. Our research has found that the introduction of a low energy, uniform ultrasound field into enzyme processing solutions greatly improved their effectiveness by significantly increasing their reaction rate. It has been established that the following specific features of combined enzyme/ultrasound bio-processing are critically important: (a) cavitation effects caused by introduction of ultrasound field into the enzyme processing solution greatly enhance the transport of enzyme macromolecules toward the substrate's surface, (b) mechanical impacts, produced by the collapse of cavitation bubbles, provide an important benefit of "opening up" the surface of solid substrates to the action of enzymes, (c) the effect of cavitation is several hundred times greater in heterogeneous systems (solid substrate–liquid) than in homogeneous, and (d) in water, the maximum effects of cavitation occur at ∼50 C, which is the optimum temperature for many enzymes. On a laboratory scale, introduction of low level, uniform ultrasonic energy in the reaction chamber during enzymatic hydrolysis of corn stover and sugar cane bagasse cellulose samples resulted in a significant improvement in enzyme efficiency. The combined enzyme/sonication hydrolysis of corn stover, bagasse and similar plant celluloses could significantly accelerate this critical step in the overall conversion of agricultural waste biomass into biofuels.