Pretreatment of lignocellulosic biomass before enzymatic hydrolysis enhances digestibility, and is intended to improve the formation of sugars while avoiding excessive degradation, and to be cost-effective.

Ultrasonication (US) in a solution causes cavitation, which is a combined phenomenon of formation, growth, and subsequent collapse of microbubbles, which produces a hot spot of localized extreme temperature and pressure (approximately 5000 °C and 500 atm). The high local energy from cavitation is known to disintegrate microcrystalline cellulose to cellulose nanofibers. Focusing on this effect, researchers have tried to apply US to the pretreatment of lignocellulosic biomass. However, the improvement in digestibility was not sufficient just by introducing US, partly because of insufficient removal of lignin.

… Recently, we reported a novel pretreatment technique combining US and SP (US-SP) for efficient degradation of lignocellulosic biomass corn stover under mild conditions. The digestibility of the biomass was greatly enhanced with the US-SP technique compared to each single pretreatment. … Here, we have proposed a novel pretreatment technique of lignocellulosic biomass employing the combination of HD cavitation and SP (HD-SP) for an efficient degradation of polysaccharides in the biomass.

—Nakashima et al.

Hydrodynamic (HD) cavitation is cavitation generated in a flowing fluid system with a constriction, such as a venturi tube or an orifice plate. When pressure at the constriction (venturi throat) falls below the vapor pressure of the liquid, HD cavities (bubbles) are generated. These bubbles subsequently collapse when the pressure increases downstream of the constriction.

HD has been studied for industrial applications such as sterilization of food and water, cell disruption, wastewater treatment, decomposition of excess sludge, generation of submicrometer emulsions, and biodiesel production. Recent studies also have shown that HD could be used for delignification of wheat straw and wood for pulp and paper manufacturing.

For their study, the researchers used corn stover as the feedstock for the new HD-SP reactor as well as the US-SP process they had developed earlier, subjected the output to enzymatic saccharification using a mixture of cellulase from Trichoderma reesei and β-glucosidase from Aspergillus niger, and characterized the results.

They found that the HD-SP pretreatment exhibited 20 times greater pretreatment efficiency than US-SP pretreatment in the enzymatic saccharification of cellulose in biomass to glucose. The HD-SP system also resulted in further increases in the production rate and yield of xylose.

Further study of pretreatment parameters such as inlet pressure, SP concentration, pretreatment temperature and time, and biomass loading could further improve pretreatment efficiency in the HD-SP system.

Resources

• Kazunori Nakashima, Yuuki Ebi, Naomi Shibasaki-Kitakawa, Hitoshi Soyama, and Toshikuni Yonemoto (2016) “Hydrodynamic Cavitation Reactor for Efficient Pretreatment of Lignocellulosic Biomass” Industrial & Engineering Chemistry Research 55 (7), 1866-1871 doi: 10.1021/acs.iecr.5b04375