Cellulosic ethanol: interactions between cultivar and enzyme loading in wheat straw processing

Jane Lindedam,Sander Bruun,Henning Jørgensen,Claus Felby,Jakob Magid

doi:10.1186/1754-6834-3-25

Abstract

BackgroundVariations in sugar yield due to genotypic qualities of feedstock are largely undescribed for pilot-scale ethanol processing. Our objectives were to compare glucose and xylose yield (conversion and total sugar yield) from straw of five winter wheat cultivars at three enzyme loadings (2.5, 5 and 10 FPU g-1 dm pretreated straw) and to compare particle size distribution of cultivars after pilot-scale hydrothermal pretreatment.ResultsSignificant interactions between enzyme loading and cultivars show that breeding for cultivars with high sugar yields under modest enzyme loading could be warranted. At an enzyme loading of 5 FPU g-1 dm pretreated straw, a significant difference in sugar yields of 17% was found between the highest and lowest yielding cultivars. Sugar yield from separately hydrolyzed particle-size fractions of each cultivar showed that finer particles had 11% to 21% higher yields than coarse particles. The amount of coarse particles from the cultivar with lowest sugar yield was negatively correlated with sugar conversion.ConclusionsWe conclude that genetic differences in sugar yield and response to enzyme loading exist for wheat straw at pilot scale, depending on differences in removal of hemicellulose, accumulation of ash and particle-size distribution introduced by the pretreatment.

Highlights

Variations in sugar yield due to genotypic qualities of feedstock are largely undescribed for pilotscale ethanol processing
Lignin (P = 0.0324) and ash content (P = 0.0004) varied between cultivars. This was due to Skalmeje displaying low lignin content after pretreatment which was significantly different from lignin-rich pretreated Smuggler and Ambition and having higher ash content than all other batches (Table 1)
We found only little xylan conversion in unfractionated samples owing to the severe hemicellulose removal during pretreatment (Table 1), and even less was found in the size fractions owing to extended washing in the fractionation process

Summary

Introduction

Variations in sugar yield due to genotypic qualities of feedstock are largely undescribed for pilotscale ethanol processing. A challenge remains, to make the process of converting lignocellulosics to biofuels cost-competitive in a large-scale process [1]. One way of achieving cost reductions and yield increments for the conversion process could be attained through improving biofeedstock quality [2]. Examples are corn stover [3,4], grasses [5], winter triticale grain [6] and winter wheat straw [7]. These studies have all employed small-scale pretreatment and hydrolysis. Since small-scale assays do not fully reflect the conditions of running a full commercial-scale pretreatment and hydrolysis, it can be questioned whether results from the small-scale assays can be extrapolated to larger-scale plants

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