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Conversion of hemicellulose and D-xylose into ethanol by the use of thermophilic anaerobic bacteria

Abstract

Ethanol is a CO{sub 2} neutral liquid fuel that can substitute the use of fossil fuels in the transportation sector, thereby reducing the CO{sub 2} emission to the atmoshpere. CO{sub 2} emission is suspected to contribute significantly to the so-called greenhouse effect, the global heating. Substrates for production of ethanol must be cheap and plentiful. This can be met by the use of lignocellulosic biomass such as willow, wheat straw, hardwood and softwood. However, the complexity of these polymeric substrates and the presence of several types of carbohydrates (glucose, xylose, mannose, galactose, arabinose) require additional treatment to release the useful carbohydrates and ferment the major carbohydrates fractions. The costs related to the ethanol-production must be kept at a minimum to be price competitive compared to gasoline. Therefore all of the carbohydrates present in lignocellulose need to be converted into ethanol. Glucose can be fermented to ethanol by yeast strains such as Saccharomyces cerevisiae, which, however, is unable to ferment the other major carbohydrate fraction, D-xylose. The need for a microorganism able to ferment D-xylose is therefore apparent. Thermophilic anaerobic ethanol producing bacteria can therefore be considered for fermentation of D-xylose. Screening of 130 thermophilic anaerobic bacterial strains, from hot-springs, mesophilic  More>>
Authors:
Publication Date:
Feb 01, 1998
Product Type:
Thesis/Dissertation
Report Number:
NEI-DK-3445
Reference Number:
SCA: 090900; PA: DK-99:001451; EDB-99:061797; SN: 99002102717
Resource Relation:
Other Information: TH: Thesis (ph.d.); PBD: Feb 1998
Subject:
09 BIOMASS FUELS; ETHANOL FUELS; BIOMASS; HEMICELLULOSE; THERMOPHILIC CONDITIONS; ANAEROBIC CONDITIONS; BACTERIA; FERMENTATION
OSTI ID:
351451
Research Organizations:
Danmarks Tekniske Univ., Lyngby (Denmark). Inst. for Miljoeteknik; Danmarks Tekniske Univ., Lyngby (Denmark)
Country of Origin:
Denmark
Language:
English
Other Identifying Numbers:
Other: ON: DE99749071; CNN: Contract ENS-1383/94-0009; ISBN 87-89220-38-2; TRN: DK9901451
Availability:
OSTI as DE99749071
Submitting Site:
DK
Size:
[133] p.
Announcement Date:

Citation Formats

Sommer, Peter. Conversion of hemicellulose and D-xylose into ethanol by the use of thermophilic anaerobic bacteria. Denmark: N. p., 1998. Web.
Sommer, Peter. Conversion of hemicellulose and D-xylose into ethanol by the use of thermophilic anaerobic bacteria. Denmark.
Sommer, Peter. 1998. "Conversion of hemicellulose and D-xylose into ethanol by the use of thermophilic anaerobic bacteria." Denmark.
@misc{etde_351451,
title = {Conversion of hemicellulose and D-xylose into ethanol by the use of thermophilic anaerobic bacteria}
author = {Sommer, Peter}
abstractNote = {Ethanol is a CO{sub 2} neutral liquid fuel that can substitute the use of fossil fuels in the transportation sector, thereby reducing the CO{sub 2} emission to the atmoshpere. CO{sub 2} emission is suspected to contribute significantly to the so-called greenhouse effect, the global heating. Substrates for production of ethanol must be cheap and plentiful. This can be met by the use of lignocellulosic biomass such as willow, wheat straw, hardwood and softwood. However, the complexity of these polymeric substrates and the presence of several types of carbohydrates (glucose, xylose, mannose, galactose, arabinose) require additional treatment to release the useful carbohydrates and ferment the major carbohydrates fractions. The costs related to the ethanol-production must be kept at a minimum to be price competitive compared to gasoline. Therefore all of the carbohydrates present in lignocellulose need to be converted into ethanol. Glucose can be fermented to ethanol by yeast strains such as Saccharomyces cerevisiae, which, however, is unable to ferment the other major carbohydrate fraction, D-xylose. The need for a microorganism able to ferment D-xylose is therefore apparent. Thermophilic anaerobic ethanol producing bacteria can therefore be considered for fermentation of D-xylose. Screening of 130 thermophilic anaerobic bacterial strains, from hot-springs, mesophilic and thermophilic biogas plants, paper pulp industries and brewery waste, were examined for production of ethanol from D-xylose and wet-oxidized hemicellulose hydrolysate. Several strains were isolated and one particular strain was selected for best performance during the screening test. This strain was characterized as a new species, Thermoanaerobacter mathranii. However, the ethanol yield on wet-oxidized hemicellulose hydrolysate was not satisfactory. The bacterium was adapted by isolation of mutant strains, now resistant to the inhibitory compounds present in the hydrolysate. Growth and ethanol yield were improved on this substrate. The growth medium for fermentation of thermophilic anaerobic bacteria is complex and therefore uneconomical on an industrial scale. It contains e.g. growth factors, like vitamins and trace elements, and co-substrates such as yeast extract. The effect of vitamin and trace element addition on viability and ethanol production was examined. It was concluded that only half of these growth factors were needed in the medium for production of ethanol. Physiological studies of thermophilic anaerobic bacteria have shown that the ethanol yield decreases at increasing substrate concentration. The biochemical limitations causing this phenomenon are not known in detail. Physiological and biochemical studies of T. mathranii, including extraction of intracellular metabolites and enzymes of the pentose phosphate pathway and glycolysis, revealed several bottlenecks in the D-xylose metabolism. This knowledge makes way for physiologicl and genetic engineering of this strain to improve the ethanol yield and productivity at high concentration of D-xylose. (au) EFP-94. 164 refs.}
place = {Denmark}
year = {1998}
month = {Feb}
}