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Link to original content: http://pubmed.ncbi.nlm.nih.gov/26210138/
Simultaneous saccharification and fermentation of steam exploded duckweed: Improvement of the ethanol yield by increasing yeast titre - PubMed Skip to main page content
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. 2015 Oct:194:263-9.
doi: 10.1016/j.biortech.2015.06.131. Epub 2015 Jul 2.

Simultaneous saccharification and fermentation of steam exploded duckweed: Improvement of the ethanol yield by increasing yeast titre

X Zhao  1 , G K Moates  1 , A Elliston  1 , D R Wilson  1 , M J Coleman  2 , K W Waldron  3
Affiliations

Simultaneous saccharification and fermentation of steam exploded duckweed: Improvement of the ethanol yield by increasing yeast titre

X Zhao et al. Bioresour Technol. 2015 Oct.

Abstract

This study investigated the conversion of Lemna minor biomass to bioethanol. The biomass was pre-treated by steam explosion (SE, 210°C, 10 min) and then subjected to simultaneous saccharification and fermentation (SSF) using Cellic® CTec 2 (20 U or 0.87 FPU g(-1) substrate) cellulase plus β-glucosidase (2 U g(-1) substrate) and a yeast inoculum of 10% (v/v or 8.0×10(7) cells mL(-1)). At a substrate concentration of 1% (w/v) an ethanol yield of 80% (w/w, theoretical) was achieved. However at a substrate concentration of 20% (w/v), the ethanol yield was lowered to 18.8% (w/w, theoretical). Yields were considerably improved by increasing the yeast titre in the inoculum or preconditioning the yeast on steam exploded liquor. These approaches enhanced the ethanol yield up to 70% (w/w, theoretical) at a substrate concentration of 20% (w/v) by metabolising fermentation inhibitors.

Keywords: Bioethanol production; Cellulase; Duckweed; Simultaneous saccharification and fermentation; Steam explosion.

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Figures

Fig. 1
Fig. 1
The identification of optimum CTec 2 dosage and comparison to CE. The enzyme dosage is cellulase: 0.87 FPU g−1 substrate, BG: 2 U g−1 substrate. Released Glc represents the amount of glucose produced by steam explosion alone. ***p < 0.001, *p < 0.05, ns = not significant (p > 0.05) compared with the sample of CE + BG.
Fig. 2
Fig. 2
A 96 h yeast culture in YM medium and various SE liquors pretreated for 10 min. at different temperatures. Glucose concentration in the SE liquors was 0.1 mg mL−1 while the concentration of YM was 10 mg mL−1. Turbidity provides an indication of the yeast cell concentration.
Fig. 3
Fig. 3
Effect of SSF conditions on ethanol yield.
Fig. 4
Fig. 4
The investigation of the digestibility of concentrated materials and their fermentation inhibition. (a) Enzymatic saccharification at different substrate concentrations. (b) Enzymatic saccharification on concentrated materials after dilution to the same dry matter contents. The samples show no significant differences (F(6, 35) = 1.77, p = 0.133).
Fig. 5
Fig. 5
Levels of fermentation inhibitors remaining after SSF using larger titres of yeast and/or preconditioned yeast.
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