Elsevier

Bioresource Technology

Volume 101, Issue 13, July 2010, Pages 4926-4929
Bioresource Technology

Bamboo saccharification through cellulose solvent-based biomass pretreatment followed by enzymatic hydrolysis at ultra-low cellulase loadings

https://doi.org/10.1016/j.biortech.2009.09.081Get rights and content

Abstract

The modified cellulose solvent- (concentrated phosphoric acid) and organic solvent- (95% ethanol) based lignocellulose fractionation (COSLIF) was applied to a naturally-dry moso bamboo sample. The biomass dissolution conditions were 50 °C, 1 atm for 60 min. Glucan digestibility was 88.2% at an ultra-low cellulase loading of one filter paper unit per gram of glucan. The overall glucose and xylose yields were 86.0% and 82.6%, respectively. COSLIF efficiently destructed bamboo’s fibril structure, resulting in a ∼33-fold increase in cellulose accessibility to cellulase (CAC) from 0.27 to 9.14 m2 per gram of biomass. Cost analysis indicated that a 15-fold decrease in use of costly cellulase would be of importance to decrease overall costs of biomass saccharification when cellulase costs are higher than $0.15 per gallon of cellulosic ethanol.

Introduction

The production of second generation biofuels (e.g., cellulosic ethanol) or third generation biofuels (e.g., hydrogen) from renewable lignocellulosic biomass will result in a new industrial revolution from a fossil fuel-based economy to a sustainable carbohydrate economy (Lynd et al., 2008, Zhang, 2008, Zhang, 2009). Cost-effective production of fermentable sugars from recalcitrant biomass remains the largest obstacle to emerging cellulosic ethanol biorefineries (Lynd et al., 2008, Wyman, 2007, Zhang, 2008). Significant advances in reduction of 20- to 30-fold of enzyme costs have been made through enzyme production process optimization and cellulase engineering (Himmel et al., 2007, Zhang et al., 2006b), but cellulase, whose costs may range from ∼30 cents to more than 100 cents per gallon of cellulosic ethanol at a typical cellulase loading of 15 filter paper units per gram of glucan, is still far more expensive than that of starch-hydrolyzing enzymes for corn kernel-based ethanol biorefineries (e.g., ∼5 cents per gallon of starch ethanol).

Bamboos are giant woody, tree-like, perennial evergreen C4 grasses with more than 70 genera and about 1000 species. Bamboos grow naturally in tropical, subtropical, and temperate regions around the world (Gratani et al., 2008). Bamboos are of economic and high cultural significance in East Asia and South East Asia. Since they are both lightweight and exceptionally durable, the treated bamboos are used extensively as building materials for houses, construction scaffolding, flooring, bridges, etc. Also, they are extensively used to make furniture, chopsticks, food steamers, paper pulp, etc., and are grown as ornamental plants. Phyllostachys pubescens (moso bamboo), one of the most popular bamboos, can grow to heights of over 20 m with a diameter of nearly 18 cm. Moso bamboo flourishes in moist, well drained, and fertilized soils with pH from 4.5 to 7.0 and annual precipitation between 800 and 1800 mm. Marginal lands, such as mountain valley, foot of mountain, and gentle slope, are suitable for moso bamboo growth.

Cellulose solvent- and organic solvent-based lignocellulose fractionation (COSLIF) has been developed to separate lignocellulose components using a cellulose solvent (concentrated phosphoric acid), an organic solvent (acetone), and water (Moxley et al., 2008, Zhang et al., 2007). High glucan enzymatic digestibility of the COSLIF-pretreated biomass is mainly attributed to large cellulose accessibility to enzymes (Zhu et al., 2009).

In this study, we investigated the feasibility of bamboo saccharification by the modified COSLIF followed by enzymatic hydrolysis at ultra-low cellulase loadings.

Section snippets

Chemicals and materials

All chemicals were reagent grade and purchased from Sigma–Aldrich (St. Louis, MO), unless otherwise noted. Phosphoric acid (85%) and ethanol (95%) were purchased from Fisher Scientific (Houston, TX). The Trichoderma cellulase (Novozyme® 50013) and beta-glucosidase (Novozyme® 50010) were gifts from Novozymes North American (Franklinton, NC). They had activities of 84 filter paper units (FPUs) per mL and 270 beta-glucosidase units per mL, respectively. The bamboo used in this study was moso

Results and discussion

The functionally-based model for enzymatic cellulose hydrolysis suggests that increasing substrate accessibility is more important than decreasing the degree of polymerization of cellulose for biomass pretreatment (Zhang and Lynd, 2006). The most efficient way for increasing cellulose accessibility is to dissolve cellulose fibers and regenerate them as amorphous form (Kuo and Lee, 2009, Zhang et al., 2006a, Zhang et al., 2006b). The COSLIF V1.0 utilizes a highly-volatile organic solvent

Conclusions

The modified COSLIF pretreatment effectively disrupt recalcitrance of bamboo, generating highly reactive cellulosic materials as shown in a high glucan digestibility of 88.2% with 1 filter paper unit per gram of glucan at hour 72. A 15-fold reduction in cellulase usage will be of great importance in profitable production of cellulosic ethanol.

Acknowledgements

Support for this work was provided to YHPZ from ITRI of Taiwan, partially from the DOD Grant (W911SR-08-P-0021), USDA-sponsored Bioprocessing and Biodesign Center, DOE BioEnergy Science Center, Dupont Young Professor Award, and ICTAS. NS was partially supported by the ICTAS scholar program.

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