Irradiating the Future of Biofuel: Using Electron Beam Irradiation Pretreatment to Improve Cellulosic Biofuel Production

Cellulose’s abundance makes it an obvious choice as a raw material for biofuel production (Bak et al. 2009). Specifically, enzymatic hydrolysis of lignocellulose, which is composed of cellulose, hemicelluloses, and lignin, has been studied to satisfy the demanding ambitions to reduce gasoline usage from groups like the United State’s Department of Energy. Unfortunately, complications arise during cellulosic biofuel manufacturing because the cellulose in lignocellulose is not normally accessible to hydrolytic enzymes. Many physical and chemical pretreatments have been suggested to improve access to the cellulose in order to produce higher glucose yields. The majority of the proposed chemical processes generate byproducts that inhibit enzymatic hydrolysis of the cellulose, establishing a need for costly, resistant enzymes. Many physical pretreatments, such as the milling process, have been deemed inefficient and energetically costly. Instead, electron beam irradiation (EBI) of lignocelluloses was proposed for its low yields of harmful byproducts and for its functionality in the absence of extreme temperatures. —Alec Faggen
Bak, J., Ko, J., Han, Y., Lee, B., Choi, I., Kim, K., 2009. Improved enzymatic hydrolysis yield of rice straw using electron beam irradiation pretreatment. Bioresource Technology 100, 12851290.

      Bak and colleagues working at the Korea University and Korea Atomic Energy Research Institute evaluated the efficacy of EBI to improve enzymatic hydrolysis of cellulose for biofuel production.  The authors of the paper pretreated a type of lignocellulose called rice straw with EBI and determined its subsequent enzymatic digestibility and physical composition. Multiple trials were performed using varying crystallinity indexes of cellulose, EBI currents, and EBI dosage to determine optimal levels for pretreatment. The authors also varied the concentration of hydrolytic enzymes, resolving that no concentration of enzymes could effectively hydrolyze the lignocellulose without proper pretreatment. Scanning electron microscopy and X-ray diffraction verified that the EBI was causing the physical changes in the rice straw. 
Compared to the control samples of untreated rice straw, EBI-treated rice straw increased glucose yields from 5.1% to 43.1% after hydrolysis for 24 hours, and from 22.6% to 52.1% after hydrolysis for 132 hours.  However, these yields were lower than other physical and chemical pretreatment methods such as dilute-acid, ammonia fiber explosion, and soaking in aqueous ammonia, documented in previous literature. 

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