Thermoanaerobacter : potential ethanol and hydrogen producers

• Main Author: Hrönn Brynjarsdóttir 1972-
• Other Authors: Háskólinn á Akureyri
• Format: Thesis
• Language: English
• Published: 2012
• Subjects: Auðlindafræði; Líftækni; Meistaraprófsritgerðir; Lífræn efnasambönd; Eldsneytisframleiðsla; Akureyri; Grensdalur; Iceland; University of Akureyri
• Online Access: http://hdl.handle.net/1946/12336

Verkefnið er lokað til 30.6.2014. Two anaerobic, thermophilic bacterial strains, isolated from hot springs in Grensdalur, SW-Iceland, were examined concerning their ability to produce biofuels (ethanol and hydrogen) from various sugars and hydrolysates of complex biomass. Fifteen isolates from the strain collection of the University of Akureyri were originally screened by ethanol and hydrogen production capacity on glucose, xylose and hydrolysates from Whatman paper (cellulose) and grass. Based on results of these cultivations one strain (AK5) was selected because of high ethanol production capacity and another strain (CMC15) with high hydrogen production capacity. A partial 16S rRNA analysis revealed that both the strains belong to the genera Thermoanaerobacter. Hydrogen and ethanol production formation from various carbon sources were investigated as well as the effects of various environmental factors (substrate concentration, effect of pH and temperature, partial pressure of hydrogen) on growth and end product formation. Effects of external electron scavenging systems on end product formation was also investigated for strain AK5. Finally, biofuel production from hydrolysates made from various lignocellulosic biomass were investigated in detail and compared with literature. Maximum ethanol production of strain AK5 is 1,7 mol/mol af glucose; 1,35 mol/mol xylose; 7,7 mM/g sellulose og 4,4 mM/g grass. During growth in the presence of electron scavenging systems the strain almost completely shifted from ethanol to acetate formation. The main flaw of the strain was its intolerance towards high glucose concentrations but this may be minimized by using fed-batch or continuous culture technique. Strain CMC15 maximally produced 3,1 mol H2/mol glucose and 4.83 mol H2/g grass hydrolysate. Similar to strain AK5 this strain was also inhibited by increasing glucose concentrations, most likely because of acetate production which results in low pH during batch culture cultivation. Thus, continuous culture with stable pH ...