Recent advancements in various steps of ethanol, butanol, and isobutanol productions from woody materials
ABSTRACT In this review, the recent advancements and technical challenges associated with the production of ethanol, butanol and isobutanol via bioconversion routes from celluloses of woody materials are reviewed. Physicochemical processes, e.g. steam explosion, seem to be the most viableprocessfor pretreating woody materials. Although enzymatic hydrolysis is selective, it is rather a slow process. Acid hydrolysis is a relatively fast process with a high yield, but it produces inhibitory compounds of fermentation, which necessitates a detoxification process prior to the fermentation. Presently, the major challenges in the production of ethanol,butanol and isobutanol via biological conversions are the ratherlow production yield and the sensitivity of microorganisms to the presence of inhibitors and productsin fermentation media. In this study, the recent advancements in the applications of S. cerevisiae,C. Acetobutylicum and C. glutamicumas, the most promising microorganisms, for ethanol, butanol and isobutanol production arealso discussed. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 2013.
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ABSTRACT: Hemicelluloses and lignin present in the spent liquor (SL) of neutral sulfite semichemical (NSSC) pulping process can potentially be converted into value-added products such as furfural, hydroxymethylfurfural, levulinic acid, phenols and adhesives. However, the direct conversion of hemicelluloses and lignin of SL into value-added products is uneconomical due to the dilute nature of the SL. To have a feasible downstream process for utilizing lignocelluloses of SL, the lignocelluloses should initially be separated from the SL. In this study, an adsorption process (via applying activated carbon) was considered for isolating the dissolved lignin and hemicelluloses from the SL of an NSSC pulping process. Under the optimal conditions of pH, SL/AC weight ratio, time and temperature of 5.7, 30, 360 min and 30 °C, the maximum lignin and hemicellulose adsorptions were 0.33 and 0.25 g/g on AC. The chemical oxygen demand (COD) and turbidity of the SL were decreased by 11% and 39%, respectively, as a result of lignocellulose adsorption on AC. Also, the incineration behavior of the SL-treated AC was studied with a thermo-gravimetric analysis (TGA).Journal of Environmental Management 04/2014; 136:62–67. DOI:10.1016/j.jenvman.2014.01.032 · 3.19 Impact Factor
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ABSTRACT: Fossil fuel reserves depletion, global warming, unrelenting population growth, and costly and problematic waste recycling call for renewable resources of energy and consumer products. As an alternative to the 100 % oil economy, production processes based on biomass can be developed. Huge amounts of lignocellulosic wastes are yearly produced all around the world. They include agricultural residues, food farming wastes, "green-grocer's wastes," tree pruning residues, and organic and paper fraction of urban solid wastes. The common ways currently adopted for disposal of these wastes present environmental and economic disadvantages. As an alternative, processes for adding value to wastes producing high added products should be developed, that is the upgrading concept: adding value to wastes by production of a product with desired reproducible properties, having economic and ecological advantages. A wide range of high added value products, such as enzymes, biofuels, organic acids, biopolymers, bioelectricity, and molecules for food and pharmaceutical industries, can be obtained by upgrading solid wastes. The most recent advancements of their production by biotechnological processes are overviewed in this manuscript.Applied Microbiology and Biotechnology 06/2013; 97(14). DOI:10.1007/s00253-013-5014-7 · 3.81 Impact Factor
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ABSTRACT: The aldehyde dehydrogenase from Thermoplasma acidophilum, which was previously implemented as a key enzyme in a synthetic cell-free reaction cascade for the production of alcohols, was optimized by directed evolution. Improvements have been made to enhance reaction velocity and solubility. Using a random approach followed by site-directed and saturation mutagenesis, three beneficial amino acid mutations were found after screening of ca. 20,000 variants. Mutation Y399C enhanced the protein solubility after recombinant expression in Escherichia coli 6-fold. Two further mutations, F34M and S405N, enhanced enzyme activity with the cofactor NAD(+) by a factor of eight. Impacts on enzyme stability and substrate specificity were negligible. Modeling of the enzyme structure did not reveal any direct interactions between the amino acid substitutions and residues of the active site or the enzyme's substrates. Thus, a directed evolution approach allowed for the generation of improved enzyme variants which were unlikely to be found by rational or semi-rational strategies.10/2013; 53(5):307-14. DOI:10.1016/j.enzmictec.2013.07.002