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  • BioEthanol : fuel of the future?
  • Meistara
  • Microbial fermentations are potential producers of sustainable energy carriers. In this
    study, 68 samples were used for the isolation of ethanol and hydrogen producing
    bacteria from various carbon substrates from geothermal springs in Iceland. 16S rRNA
    analysis revealed that most of low temperature (50°C) enrichments indicated the
    presence of bacteria belonging to Thermoanaerobacterium, Caloramator and
    Clostridium. At higher temperatures (60°C) Thermoanaerobacterium and
    Thermoanaerobacter became more dominant and at 70 and 75°C only members of the
    genera Thermoanaerobacter and Caldicellulosiruptor were present. Low temperature
    enrichments (50°C) produced mainly ethanol, acetate and butyrate from monosugar
    fermentation and two enrichments produced more than 1.3 mol-EtOH/mol-glucose and
    two enrichments produced more than 1.0 mol-EtOH/mol xylose. Most of the
    enrichments that directed their carbon flow to ethanol belong to Caloramator,
    Paenibacillus and Thermoanaerobacterium. At higher temperatures, several
    enrichments produced more than 1.0 mol-EtOH/mol-glucose and xylose, especially at
    60°C, mostly belonging to Thermoanaerobacter and Thermoanaerobacterium. Butyrate
    was only detected in one of the 18 enrichments at 60°C and not at higher temperatures.
    Only one enrichment of a total of 16 at 70 and 75°C produced more than 1.0 mol-
    EtOH/mol glucose but the carbon flow was directed more towards acetate and hydrogen
    formation. Seven cultures were investigated further with respect to phylogeny and
    physiology. Six of the strains belonged to Thermoanaerobacterium and one to
    Paenibacillus. Basic characteristics concerning Topt and pHopt were performed on all
    seven strains, indicating that the Thermoanaerobacterium strain grow best at around
    60°C and at low pH between 5 and 6. The Paenibacillus strain was a moderate
    thermophile (Topt; 50°C) and had a pHopt at 8.0. Paenibacillus was the fastest growing
    bacterium with the shortest generation time of 0.39 h (pHopt) and 0.71 h (Topt). The
    Thermoanaerobacterium strains showed generation times between 0.81h to 1.99h. All
    strains were highly saccharolytic degrading broad spectrum of pentoses, hexoses and
    disaccharides as well as xylan and pectin. All strains produced more than 1 mol-
    EtOH/mol-glucose and xylose and could grow in the presence of 3.2% ethanol (v/v) but
    not at 6.4%. Different initial substrate loadings (glucose) indicated that at glucose
    concentrations between 50 and 100 mM, a clear inhibition occurred leading to
    inefficient glucose degradation and lower end product formation. Growth of two strains AK66 and AK17 was also investigated on hydrolysates (0.75% w/v) made from cellulose
    (Whatman paper), newspaper, hemp leaves and hemp fibers (Cannabis sativa), barley
    straw (Hordeum vulgare) and grass (Phleum pratense). End product formation was
    analyzed from the cultures after fermentation. Strain AK66 produced most ethanol (20 to
    24 mM) from cellulose but weak acid and base pretreatment did not enhance ethanol
    yields. On other biomass types, lower ethanol yield were observed (lowest on barley
    straw; 4 mM, highest on hemp stem, 12 mM) but were increased significically by
    pretreatments. Yields of ethanol by strain AK17 were considerable higher, ranging from
    5 mM on hemp leaves to 50 mM on pure cellulose. Acidic pretreatment enhanced
    ethanol yields mostly on hemp leaves (5 mM to 18 mM) and base pretreatment on grass
    (20 mM to 28 mM). Other products from hydrolysate fermentation for both strains were
    acetate, carbon dioxide and hydrogen, but in lower amounts.

  • 25.6.2009

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Hilma_FV_2009_fixed.pdf2.1 MBOpinnBioEthanol - heildPDFSkoða/Opna