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  • 1. Christakopoulos, Paul
    et al.
    Koullas, Dimitrios P.
    Department of Chemical Engineering, National Technical University of Athens.
    Kekos, Dimitris
    Department of Chemical Engineering, National Technical University of Athens.
    Macris, Basil J
    Department of Chemical Engineering, National Technical University of Athens.
    Koukios, Emmanuel G.
    Department of Chemical Engineering, National Technical University of Athens.
    Correlating the effect of pretreatment on the enzymatic hydrolysis of straw1992In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 39, no 1, p. 113-116Article in journal (Refereed)
    Abstract [en]

    Avicell, Alkali-treated straw cellulose (ATSC), and wheat straw were ball-milled to reduce crystallinity; wheat straw was delignified by hot (120°C) sodium hydroxide solutions of various concentrations. The physically and chemically pretreated cellulosic materials were hydrolyzed by the cellulases of Fusarium oxysporum strain F3. Enzymic hydrolysis data were fitted by the hyperbolic correlation of Holtzapple, which involves two kinetic parameters, the maximum conversion (x(max)), and the enzymic hydrolysis time corresponding to 50% of x(max) (t( 1/2 )). An empirical correlation between x(max) and cellulose crystallinity, lignin content, and degree of delignification has been found under our experimental conditions. Complete cellulose hydrolysis is shown to be possible at less than 60% crystallinity indices or less than 10% lignin content. Avicell, Alkali-treated straw cellulose (ATSC), and wheat straw were ball-milled to reduce crystallinity; wheat straw was delignified by hot (120°C) sodium hydroxide solutions of various concentrations. The physically and chemically pretreated cellulosic materials were hydrolyzed by the cellulases of Fusarium oxysporum strain F3. Enzymic hydrolysis data were fitted by the hyperbolic correlation of Holtzapple, which involves two kinetic parameters, the maximum conversion (xmax), and the enzymic hydrolysis time corresponding to 50% of Xmax (t1/2). An empirical correlation between Xmax and cellulose crystallinity, lignin content, and degree of delignification has been found under our experimental conditions. Complete cellulose hydrolysis is shown to be possible at less than 60% crystallinity indices or less than 10% lignin content.

  • 2. Gahan, Chandra Sekhar
    et al.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    Dopson, Mark
    Department of Molecular Biology, Umeå University.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Effect of chloride on ferrous iron oxidation by a Leptospirillum ferriphilum-dominated chemostat culture2010In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 106, no 3, p. 422-431Article in journal (Refereed)
    Abstract [en]

    Biomining is the use of microorganisms to catalyze metal extraction from sulfide ores. However, the available water in some biomining environments has high chloride concentrations and therefore, chloride toxicity to ferrous oxidizing microorganisms has been investigated. Batch biooxidation of Fe2+ by a Leptospirillum ferriphilum-dominated culture was completely inhibited by 12 g L-1 chloride. In addition, the effects of chloride on oxidation kinetics in a Fe2+ limited chemostat were studied. Results from the chemostat modeling suggest that the chloride toxicity was attributed to affects on the Fe2+ oxidation system, pH homeostasis, and lowering of the proton motive force. Modeling showed a decrease in the maximum specific growth rate (µmax) and an increase in the substrate constant (Ks) with increasing chloride concentrations, indicating an effect on the Fe2+ oxidation system. The model proposes a lowered maintenance activity when the media was fed with 2 to 3 g L-1 chloride with a concomitant drastic decrease in the true yield (Ytrue). This model helps to understand the influence of chloride on Fe2+ biooxidation kinetics.

  • 3.
    Li, Zhenglun
    et al.
    Michigan State University.
    Chen, Charles H.
    Michigan State University.
    Liu, Tongjun
    Michigan State University.
    Mathrubootham, Vaidyanathan
    Michigan State University.
    Hegg, Eric L.
    Michigan State University.
    Hodge, David
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Catalysis with Cuii(bpy) improves alkaline hydrogen peroxide pretreatment2013In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 110, no 4, p. 1078-1086Article in journal (Refereed)
    Abstract [en]

    Copper(II) 2,2′-bipyridine (CuII(bpy))-catalyzed alkaline hydrogen peroxide (AHP) pretreatment was performed on three biomass feedstocks including alkali pre-extracted switchgrass, silver birch, and a hybrid poplar cultivar. This catalytic approach was found to improve the subsequent enzymatic hydrolysis of plant cell wall polysaccharides to monosaccharides for all biomass types at alkaline pH relative to uncatalyzed pretreatment. The hybrid poplar exhibited the most significant improvement in enzymatic hydrolysis with monomeric sugar release and conversions more than doubling from 30% to 61% glucan conversion, while lignin solubilization was increased from 36.6% to 50.2% and hemicellulose solubilization was increased from 14.9% to 32.7%. It was found that CuII(bpy)-catalyzed AHP pretreatment of cellulose resulted in significantly more depolymerization than uncatalyzed AHP pretreatment (78.4% vs. 49.4% decrease in estimated degree of polymerization) and that carboxyl content the cellulose was significantly increased as well (fivefold increase vs. twofold increase). Together, these results indicate that CuII(bpy)-catalyzed AHP pretreatment represents a promising route to biomass deconstruction for bioenergy applications

  • 4.
    Sundkvist, Jan-Eric
    et al.
    Boliden Mineral AB.
    Gahan, Chandra Sekhar
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Modeling of ferrous iron oxidation by a Leptospirillum ferrooxidans-dominated chemostat culture2008In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 99, no 2, p. 378-389Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to evaluate a direct classical bioengineering approach to model data generated from continuous bio-oxidation of Fe2+ by a Leptospirillum ferrooxidans-dominated culture fed with either 9 g or 18 g Fe2+ L-1 under chemostat conditions (dilution rates were between 0.051 and 0.094 h-1). The basic Monod and Pirt equations have successfully been integrated in an overall mass balance procedure, which has not been previously presented in this detail for Fe2+ oxidation. To ensure chemostat conditions, it was found that the range of the dilution rates had to be limited. A too long retention time might cause starvation or non-negligible death rate whereas, a too short retention time may cause a significant alteration in solution chemistry and culture composition. Modeling of the experimental data suggested that the kinetic- and yield parameters changed with the overall solution composition. However, for respective feed solutions only minor changes of ionic strength and chemical speciation can be expected within the studied range of dilution rates, which was confirmed by thermodynamic calculations and conductivity measurements. The presented model also suggests that the apparent Fe3+ inhibition on specific Fe2+ utilization rate was a direct consequence of the declining biomass yield on Fe2+ due to growth uncoupled Fe2+ oxidation when the dilution rate was decreased. The model suggested that the maintenance activities contributed up to 90% of the maximum specific Fe2+ utilization rate, which appears close to the critical dilution rate.

  • 5.
    Tomek, Kyle J.
    et al.
    Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing.
    Saldarriaga, Carlos Rafael Castillo
    Department of Chemical and Environmental Engineering, Universidad Nacional de Colombia, Bogotá.
    Velasquez, Fernando Peregrino Cordoba
    Department of Chemical and Environmental Engineering, Universidad Nacional de Colombia, Bogotá.
    Liu, Tongjun
    DOE-Great Lakes Bioenergy Research Center, Michigan State University, East Lansing.
    Hodge, David
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Whitehead, Timothy A.
    Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing.
    Removal and upgrading of lignocellulosic fermentation inhibitors by in situ biocatalysis and liquid-liquid extraction2015In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 112, no 3, p. 627-632Article in journal (Refereed)
    Abstract [en]

    Hydroxycinnamic acids are known to inhibit microbial growth during fermentation of lignocellulosic biomass hydrolysates, and the ability to diminish hydroxycinnamic acid toxicity would allow for more effective biological conversion of biomass to fuels and other value-added products. In this work, we provide a proof-of-concept of an in situ approach to remove these fermentation inhibitors through constituent expression of a phenolic acid decarboxylase combined with liquid-liquid extraction of the vinyl phenol products. As a first step, we confirmed using simulated fermentation conditions in two model organisms, Escherichia coli and Saccharomyces cerevisiae, that the product 4-vinyl guaiacol is more inhibitory to growth than ferulic acid. Partition coefficients of ferulic acid, p-coumaric acid, 4-vinyl guaiacol, and 4-ethyl phenol were measured for long-chain primary alcohols and alkanes, and tetradecane was identified as a co-solvent that can preferentially extract vinyl phenols relative to the acid parent and additionally had no effect on microbial growth rates or ethanol yields. Finally, E. coli expressing an active phenolic acid decarboxylase retained near maximum anaerobic growth rates in the presence of ferulic acid if and only if tetradecane was added to the fermentation broth. This work confirms the feasibility of donating catabolic pathways into fermentative microorganisms in order to ameliorate the effects of hydroxycinnamic acids on growth rates, and suggests a general strategy of detoxification by simultaneous biological conversion and extraction.

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