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  • 1. Brandberg, T.
    et al.
    Karimi, K.
    University of Borås, School of Engineering.
    Taherzadeh, M.J.
    University of Borås, School of Engineering.
    Franzén, C.J.
    Gustafsson, L.
    Continuous fermentation of wheat-supplemented lignocellulose hydrolysate with different types of cell retention2007In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 98, no 1, p. 80-Article in journal (Refereed)
    Abstract [en]

    Medium supplementation and process alternatives for fuel ethanol production from dilute acid lignocellulose hydrolysate were investigated. Dilute acid lignocellulose hydrolysate supplemented with enzymatically hydrolysed wheat flour could sustain continuous anaerobic cultivation of Saccharomyces cerevisiae ATCC 96581 if further supplemented with ammonium sulphate and biotin. This medium composition allowed for a hexose utilisation of 73% and an ethanol production of 36 mmol l-1 h-1 in chemostat cultivation at dilution rate 0.10 h-1. Three different methods for cell retention were compared for improved fermentation of supplemented lignocellulose hydrolysate: cell recirculation by filtration, cell recirculation by sedimentation and cell immobilisation in calcium alginate. All three cell retention methods improved the hexose conversion and increased the volumetric ethanol production rate. Recirculation of 75% of the bioreactor outlet flow by filtration improved the hexose utilisation from 76% to 94%. Sedimentation turned out to be an efficient method for cell separation; the cell concentration in the reactor was 32 times higher than in the outflow after 60 h of substrate feeding. However, chemostat and continuous cell recirculation cultures became severely inhibited when the dilution rate was increased to 0.20 h-1. In contrast, an immobilised system kept producing ethanol at a stable level also at dilution rate 0.30 h-1. Biotechnol. Bioeng. 2007; 98: 80-90. © 2007 Wiley Periodicals, Inc.

  • 2.
    Horváth, I. S.
    et al.
    Department of Chemical Reaction Engineering, Chalmers University of Technology.
    Taherzadeh, Mohammad J
    Department of Chemical Reaction Engineering, Chalmers University of Technology.
    Niklasson, C.
    Department of Chemical Reaction Engineering, Chalmers University of Technology.
    Lidén, G.
    Department of Chemical Engineering II, Lund Institute of Technology.
    Effects of furfural on anaerobic continuous cultivation of Saccharomyces cerevisiae2001In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 75, no 5, p. 540-549Article in journal (Refereed)
    Abstract [en]

    Furfural is an important inhibitor of yeast metabolism in lignocellulose-derived substrates. The effect of furfural on the physiology of Saccharomyces cerevisiae CBS 8066 was investigated using anaerobic continuous cultivations. Experiments were performed with furfural in the feed medium (up to 8.3 g/L) using three dierent dilution rates (0.095, 0.190, and 0.315 h-1). The measured concentration of furfural was low (<0.1 g/L) at all steady states obtained. However, it was not possible to achieve a steady state at a specific conversion rate of furfural, qf, higher than approximately 0.15 g/g·h. An increased furfural concentration in the feed caused a decrease in the steady-state glycerol yield. This agreed well with the decreased need for glycerol production as a way to regenerate NAD+, i.e., to function as a redox sink because furfural was reduced to furfuryl alcohol. Transient experiments were also performed by pulse addition of furfural directly into the fermentor. In contrast to the situation at steady-state conditions, both glycerol and furfuryl alcohol yields increased after pulse addition of furfural to the culture. Furthermore, the maximum specific conversion rate of furfural (0.6 g/g·h) in dynamic experiments was significantly higher than what was attainable in the chemostat experiments. The dynamic furfural conversion could be described by the use of a simple Michaelis-Menten-type kinetic model. Also furfural conversion under steady-state conditions could be explained by a Michaelis-Menten-type kinetic model, but with a higher anity and a lower maximum conversion rate. This indicated the presence of an additional component with a higher anity, but lower maximum capacity, either in the transport system or in the conversion system of furfural.

  • 3. Jeihanipour, A.
    et al.
    Karimi, K.
    University of Borås, School of Engineering.
    Taherzadeh, Mohammad
    University of Borås, School of Engineering.
    Enhancement of ethanol and biogas production from high-crystalline cellulose by different modes of NMO pretreatment2010In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 105, no 3, p. 469-476Article in journal (Refereed)
    Abstract [en]

    Pretreatment of high-crystalline cellulose with N-methyl-morpholine-N-oxide (NMO or NMMO) to improve bioethanol and biogas production was investigated. The pretreatments were performed at 90 and 120°C for 0.5–15 h in three different modes, including dissolution (85% NMO), ballooning (79% NMO), and swelling (73% NMO). The pretreated materials were then enzymatically hydrolyzed and fermented to ethanol or anaerobically digested to biogas (methane). The pretreatment at 85% NMO, 120°C and 2.5 h resulted in 100% yield in the subsequent enzymatic hydrolysis and around 150% improvement in the yield of ethanol compared to the untreated and water-treated material. However, the best results of biogas production were obtained when the cellulose was treated with swelling and ballooning mode, which gave almost complete digestion in 15 days. Thus, the pretreatment resulted in 460 g ethanol or 415 L methane from each kg of cellulose. Analysis of the structure of treated and untreated celluloses showed that the dissolution mode can efficiently convert the crystalline cellulose I to cellulose II. However, it decreases the water swelling capacity of the cellulose. On the other hand, swelling and ballooning modes in NMO treatment were less efficient in both water swelling capacity and cellulose crystallinity. No cellulose loss, ambient pressure, relatively moderate conditions, and high efficiency make the NMO a good alternative for pretreatment of high-crystalline cellulosic materials.

  • 4.
    Taherzadeh, Mohammad J
    et al.
    Dept. of Chem. Reaction Engineering, Chalmers University of Technology.
    Niklasson, C.
    Dept. of Chem. Reaction Engineering, Chalmers University of Technology.
    Lidén, G.
    Dept. of Chemical Engineering II, Lund Institute of Technology.
    On-line control of fed-batch fermentation of dilute-acid hydrolyzates2000In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 69, no 3, p. 330-338Article in journal (Refereed)
    Abstract [en]

    Dilute-acid hydrolyzates from lignocellulose are, to a varying degree, inhibitory to yeast. In the present work, dilute-acid hydrolyzates from spruce, birch, and forest residue, as well as synthetic model media, were fermented by Saccharomyces cerevisiae in fed-batch cultures. A control strategy based on on-line measurement of carbon dioxide evolution (CER) was used to control the substrate feed rate in a lab scale bioreactor. The control strategy was based solely on the ratio between the relative increase in CER and the relative increase in feed rate. Severely inhibiting hydrolyzates could be fermented without detoxification and the time required for fermentation of moderately inhibiting hydrolyzates was also reduced. The feed rate approached a limiting value for inhibiting media, with a corresponding pseudo steady-state value for CER. However, a slow decrease of CER with time was found for media containing high amounts of 5-hydroxymethyl furfural (HMF). The success of the control strategy is explained by the conversion of furfural and HMF by the yeast during fed-batch operation. The hydrolyzates contained between 1.4 and 5 g/l of furfural and between 2.4 and 6.5 g/l of HMF. A high conversion of furfural was obtained (between 65-95%) at the end of the feeding phase, but the conversion of HMF was considerably lower (between 12-40%). (C) 2000 John Wiley and Sons, Inc.Dilute-acid hydrolyzates from lignocellulose are, to a varying degree, inhibitory to yeast. In the present work, dilute-acid hydrolyzates from spruce, birch, and forest residue, as well as synthetic model media, were fermented by Saccharomyces cerevisiae in fed-batch cultures. A control strategy based on on-line measurement of carbon dioxide evolution (CER) was used to control the substrate feed rate in a lab scale bioreactor. The control strategy was based solely on the ratio between the relative increase in CER and the relative increase in feed rate. Severely inhibiting hydrolyzates could be fermented without detoxification and the time required for fermentation of moderately inhibiting hydrolyzates was also reduced. The feed rate approached a limiting value for inhibiting media, with a corresponding pseudo steady-state value for CER. However, a slow decrease of CER with time was found for media containing high amounts of 5-hydroxymethyl furfural (HMF). The success of the control strategy is explained by the conversion of furfural and HMF by the yeast during fed-batch operation. The hydrolyzates contained between 1.4 and 5 g/l of furfural and between 2.4 and 6.5 g/l of HMF. A high conversion of furfural was obtained (between 65-95%) at the end of the feeding phase, but the conversion of HMF was considerably lower (between 12-40%).

  • 5.
    Talebnia, F.
    et al.
    Department of Chemical Engineering and Environmental Science, Chalmers University of Technology.
    Niklasson, C.
    Department of Chemical Engineering and Environmental Science, Chalmers University of Technology.
    Taherzadeh, Mohammad J
    University of Borås, Faculty of Textiles, Engineering and Business.
    Ethanol production from glucose and dilute-acid hydrolyzates by encapsulated S. cerevisiae2005In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 90, no 3, p. 345-353Article in journal (Refereed)
    Abstract [en]

    The performance of encapsulated Saccharomyces cerevisiae CBS 8066 in anaerobic cultivation of glucose, in the presence and absence of furfural as well as in dilute-acid hydrolyzates, was investigated. The cultivation of encapsulated cells in 10 sequential batches in synthetic media resulted in linear increase of biomass up to 106 g/L of capsule volume, while the ethanol productivity remained constant at 5.15 (±0.17) g/L·h (for batches 6-10). The cells had average ethanol and glycerol yields of 0.464 and 0.056 g/g in these 10 batches. Addition of 5 g/L furfural decreased the ethanol productivity to a value of 1.31 (±0.10) g/L·h with the encapsulated cells, but it was stable in this range for five consecutive batches. On the other hand, the furfural decreased the ethanol yield to 0.41-0.42 g/g and increased the yield of acetic acid drastically up to 0.068 g/g. No significant lag phase was observed in any of these experiments. The encapsulated cells were also used to cultivate two different types of dilute-acid hydrolyzates. While the free cells were not able to ferment the hydrolyzates within at least 24 h, the encapsulated yeast successfully converted glucose and mannose in both of the hydrolyzates in less than 10 h with no significant lag phase. However, since the hydrolyzates were too toxic, the encapsulated cells lost their activity gradually in sequential batches. 

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