title: How chip size impacts steam pretreatment effectiveness for biological conversion of poplar wood into fermentable sugars.
abstract: BACKGROUND
  Woody biomass is highly recalcitrant to enzymatic sugar release and often requires significant size reduction and severe pretreatments to achieve economically viable sugar yields in biological production of sustainable fuels and chemicals. However, because mechanical size reduction of woody biomass can consume significant amounts of energy, it is desirable to minimize size reduction and instead pretreat larger wood chips prior to biological conversion. To date, however, most laboratory research has been performed on materials that are significantly smaller than applicable in a commercial setting. As a result, there is a limited understanding of the effects that larger biomass particle size has on the effectiveness of steam explosion pretreatment and subsequent enzymatic hydrolysis of wood chips.
  
  
  RESULTS
  To address these concerns, novel downscaled analysis and high throughput pretreatment and hydrolysis (HTPH) were applied to examine whether differences exist in the composition and digestibility within a single pretreated wood chip due to heterogeneous pretreatment across its thickness. Heat transfer modeling, Simons' stain testing, magnetic resonance imaging (MRI), and scanning electron microscopy (SEM) were applied to probe the effects of pretreatment within and between pretreated wood samples to shed light on potential causes of variation, pointing to enzyme accessibility (i.e., pore size) distribution being a key factor dictating enzyme digestibility in these samples. Application of these techniques demonstrated that the effectiveness of pretreatment of Populus tremuloides can vary substantially over the chip thickness at short pretreatment times, resulting in spatial digestibility effects and overall lower sugar yields in subsequent enzymatic hydrolysis.
  
  
  CONCLUSIONS
  These results indicate that rapid decompression pretreatments (e.g., steam explosion) that specifically alter accessibility at lower temperature conditions are well suited for larger wood chips due to the non-uniformity in temperature and digestibility profiles that can result from high temperature and short pretreatment times. Furthermore, this study also demonstrated that wood chips were hydrated primarily through the natural pore structure during pretreatment, suggesting that preserving the natural grain and transport systems in wood during storage and chipping processes could likely promote pretreatment efficacy and uniformity.
authors.affiliation: Department of Chemical and Environmental Engineering, University of California, Riverside, Riverside, CA 92507 USA ; Center for Environmental Research and Technology, Bourns College of Engineering, University of California, Riverside, 1084 Columbia Ave, Riverside, CA 92507 USA ; BESC BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA ; DuPont Industrial Biosciences, 925 Page Mill Road, Palo Alto, CA 94303 USA.
authors.forename: Jaclyn D
authors.initials: JD
authors.lastname: DeMartini
authors.affiliation: BESC BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA ; School of Chemistry and Biochemistry, Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th St., Atlanta, GA 30332 USA ; Department of Energy, Environmental and Chemical Engineering, Washington University, 1 Brookings Drive, Saint Louis, MO 63130 USA.
authors.forename: Marcus
authors.initials: M
authors.lastname: Foston
authors.affiliation: BESC BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA ; School of Chemistry and Biochemistry, Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th St., Atlanta, GA 30332 USA.
authors.forename: Xianzhi
authors.initials: X
authors.lastname: Meng
authors.affiliation: BESC BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA ; School of Chemistry and Biochemistry, Institute of Paper Science and Technology, Georgia Institute of Technology, 500 10th St., Atlanta, GA 30332 USA.
authors.forename: Seokwon
authors.initials: S
authors.lastname: Jung
authors.affiliation: Department of Chemical and Environmental Engineering, University of California, Riverside, Riverside, CA 92507 USA ; Center for Environmental Research and Technology, Bourns College of Engineering, University of California, Riverside, 1084 Columbia Ave, Riverside, CA 92507 USA ; BESC BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Kumar
authors.affiliation: BESC BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA ; Joint Institute for Biological Sciences, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA ; Department of Chemical and Biomolecular Engineering, Center for Renewable Carbon, University of Tennessee, Knoxville, TN 37996-2200 USA ; Department of Forestry, Wildlife, and Fisheries, Center for Renewable Carbon, University of Tennessee, Knoxville, TN 37996-2200 USA.
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Ragauskas
authors.affiliation: Department of Chemical and Environmental Engineering, University of California, Riverside, Riverside, CA 92507 USA ; Center for Environmental Research and Technology, Bourns College of Engineering, University of California, Riverside, 1084 Columbia Ave, Riverside, CA 92507 USA ; BESC BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Wyman
keywords: Biofuels; Digestibility; Enzymes; Particle size; Pretreatment; Wood chip; Woody biomass