Cellulosic Biomass Pretreatment and Sugar Yields as a Function of Biomass Particle Size

<div><p>Three lignocellulosic pretreatment techniques (ammonia fiber expansion, dilute acid and ionic liquid) are compared with respect to saccharification efficiency, particle size and biomass composition. In particular, the effects of switchgrass particle size (32–200) on each pretreatment regime are examined. Physical properties of untreated and pretreated samples are characterized using crystallinity, surface accessibility measurements and scanning electron microscopy (SEM) imaging. At every particle size tested, ionic liquid (IL) pretreatment results in greater cell wall disruption, reduced crystallinity, increased accessible surface area, and higher saccharification efficiencies compared with dilute acid and AFEX pretreatments. The advantages of using IL pretreatment are greatest at larger particle sizes (>75 µm).</p></div

Representative plot for nitrogen porosimetry experiments.

<p>Nitrogen adsorption isotherms are shown for 32–50 mesh samples of untreated and pretreated switchgrass.</p

The yield of reducing sugar after enzymatic hydrolysis is shown for different particle size fractions for each pretreatment regime.

<p>The yield of reducing sugar after enzymatic hydrolysis is shown for different particle size fractions for each pretreatment regime.</p

Crystallinity index derived from XRD pattern.

<p>Data shown are a representation of three independent measurements (see Material and Methods).</p

SEM images of untreated and pretreated switchgrass.

<p>A –untreated, B – AFEX-pretreated, C – dilute acid pretreated, D – ionic liquid pretreated.</p

Compositional analysis of untreated and pretreated switchgrass.

<p>Compositional analysis was performed on milled biomass prior to fractionation. Data shown are a representation of three independent measurements (see Material and Methods).</p

BET surface areas of the biomass samples (m²/g).

<p>Data shown are a representation of three independent measurements (see Material and Methods).</p

Relative specific activities of Cel5A_<i>Tma</i> variants with different combinations of mutations.

<p>Note: CMC, carboxymethyl cellulose; ILSG, ionic liquid treated switchgrass; WT, wild type of Cel5A_Tma.</p

The relative activity of Cel5A_<i>Tma</i> under six different error rates was used to determine the optimal error rate for library construction.

<p>The proportion of null mutants produced using an error rate M1.4 (29 ng of <i>cel</i>5a_<i>Tma</i> gene) was ∼34 %, which indicated that the library constructed using the M1.4 error rate was suitable. The average mutation rate in the M1.4 library was ∼4.8 bp/kb gene (0.48 %)To determine the optimal error rate for Cel5A_<i>Tma</i> mutation, mutant libraries were constructed using six different error rates.</p

Mutation spectrum of Mutazyme II in error-prone PCR of cel5a_<i>Tma</i>.

<p>Mutation spectrum of Mutazyme II in error-prone PCR of cel5a_<i>Tma</i>.</p