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The conversion of monosaccharides in organe peel hydrolysates to ethanol by recombinant Escherichia coli KO11 has been investigated in pH-controlled batch fermentations at 32 and 37°C. pH values and concentration of peel hydrolysate were varied to determine approximate optimal conditions and limitations of these fermentations. Very high yields of ethanol were achieved by this microorganism at reasonable ethanol concentrations (28-48 g/L). The pH range between 5.8 and 6.2 appears to be optimal. The microorganism can convert all major monosaccharides in organe peel hydrolysates to ethanol and to smaller amounts of acetic and lactic acids. Acetic acid is coproduced in equimolar amounts with ethanol by catabolism of salts of galacturonic acid. [ABSTRACT FROM AUTHOR]

Ethanol was produced from xylose by converting the sugar to xylulose, using commercial xylose isomerases, and simultaneously converting the xylulose to ethanol by anaerobic fermentation using different yeast strains. The process was optimized with the yeast strain Schizosaccharomyces pombe (Y-164). The data show that the simultaneous fermentation and isomerization of 6% xylose can produce final ethanol concentrations of 2.1% w/v within 2 days at temperatures as high as 39°C. [ABSTRACT FROM AUTHOR]

The successful production of novel biodegradable plastic copolymers incorporating both synthetic plastic formulations, such as polystyrene, and naturally occurring biodegradable polymer components, such as cellulose, starch, or xylan, requires stable chemical bonding between these polymers. Modification of the natural polymers through acetylation of the available hydroxyl groups permits the formation of appropriate film-forming plastic copolymers. However, modification of natural polymers has been demonstrated to result in decreased attack by microbial catalysts. For this study, the abundant natural polymers cellulose, starch, and xylan were substituted with acetate to various degrees, and the effect of this modification on the anaerobic biodegradation was assessed using the biochemical methane potential (BMP) protocol. Significant reduction in anaerobic biodegradability resulted with all polymers at substitution levels of between 1.2-1.7. For the xylan acetate series, the trends for anaerobic biodegradation were in good agreement with reduced enzymatic hydyolysis using commercially available xylanase preparations. [ABSTRACT FROM AUTHOR]

The thermal denaturation of four purified Trichoderma reesei cellulase components, cellobiohydrolase (CBH) I, CBH II, endoglucanase (EG) I, and EG II, has been monitored using a combination of classical temperature/activity profiles, differential scanning calorimetry (DSC), and thermal scanning fluorescence emission spectrometry. Significant correlations were found between the results of enzyme activity studies and the results obtained through the more direct physical approaches, in that both DSC and the activity studies showed EG II (T = 75°C) to be much more thermostable (by 10-11 °C) than the other three enzymes, all three of which were shown by both activity profiles and DSC to be very similar in thermal stability. The temperature dependence of the wavelength of maximum tryptophan emission showed a parallel result, with the three enzymes exhibiting less thermostable activity being grouped together in this regard, and EG II differing from the other three in maintaining a less-exposed tryptophan microenvironment at temperatures as high as 73 °C. The DSC results suggested that at least two transitions are involved in the unfolding of each of the cellulase components, the first (lower-temperature) of which may be the one correlated with activity loss. [ABSTRACT FROM AUTHOR]

Wheat straw was pretreated with dilute (0.5%) sulfuric acid at 140°C for 1 h. Pretreated straw solids were washed with deionized water to neutrality and then stored frozen at -20°C. The approximate composition of the pretreated straw solids was 64% cellulose, 33% lignin, and 2% xylan. The cellulose in the pretreated wheat straw solids was converted to ethanol in batch simultaneous saccharification and fermentation experiments at 37°C using cellulase enzyme from Trichoderma reesei (Genencor 150 L) with or without supplementation with β-glucosidase from Aspergillus niger (Novozyme 188) to produce glucose sugar and the yeast Saccharomyces cerevisiae to ferment the glucose into ethanol. The initial cellulose concentrations were adjusted to 7.5, 10, 12.5, 15, 17.5, and 20% (w/w). Since wheat straw particles do not form slurries at these concentrations and cannot be mixed with conventional impeller mixers used in laboratory fermenters, a simple rotary fermenter was designed and fabricated for these experiments. The results of the simultaneous saccharification and fermentation (SSF) experiments indicate that the cellulose in pretreated wheat straw can be efficiently fermented into ethanol for up to a 15% cellulose concentration (24.4% straw concentration). [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass is one of the most plentiful and potentially cheapest feedstocks for ethanol production. The cellulose component can be broken down into glucose by enzymes and then converted to ethanol by yeast. However, hydrolysis of cellulose to glucose is difficult, and some form of pretreatment is necessary to increase the susceptibility of cellulose to enzymatic attack. An analysis has been completed of two pretreatment options, dilute sulfuric acid hydrolysis and sulfur dioxide impregnated steam explosion, for two feedstocks, wheat straw and aspen wood chips. Detailed process flow sheets and material and energy balances were used to generate equipment cost information. A technical and economic analysis compared the two feedstocks for each of the two pretreatments. For the same pretreatment, sugars produced from aspen wood hydrolysis were cheaper because of the higher carbohydrate content of aspen, whereas dilute acid pretreatment is favored over acid-catalyzed steam explosion. [ABSTRACT FROM AUTHOR]

As a prerequisite for the enzymatic saccharification or simultaneous saccharification and fermentation process for ethanol synthesis, a dilute-acid pretreatment of the biomass has been shown to be a very effective first step in the yeast-catalyzed bioprocess. Three hardwoods (silver maple, sycamore, and black locust) and two corn residues (cobs and stover) were chosen and subjected to prehydrolysis with dilute sulfuric acid at 140 and 160 °C for reaction times ranging from 5 to 60 min. Although the hemicelluloses from all five samples could be completely hydrolyzed at both 140 and 160 °C, hydrolysis at 160 °C for the woods and stover produced a superior substrate for the cellulase enzyme from Trichoderma reesei, in which > 90% of the cellulose was hydrolyzed by the enzyme. Corn cobs produced an excellent substrate after only 5 min at 140°C. Small amounts of lignin and glucan were also solubilized by the acid in all samples. [ABSTRACT FROM AUTHOR]

Acidothermus cellulolyticus, an isolate from hot springs at Yellowstone National Park, produced cellulase enzyme when grown in cellobiose-containing medium. The cellulase production, cell growth, and cellobiose degradation rates of batch culture in 2.5, 5.0, 7.5, and 10.0 g/L of cellobiose as a substrate were studied. The specific growth rates were measured, and the μ and K values based on these data were 0.2 h and 0.3 g cellobiose/L using the Monod equation. The maximum cellulase activities (21-69 U/L) and volumetric productivities (between 0.92 and 2.49 U/L-h) were proportional to the concentration of cellobiose. Greatest cellulase production in batch culture was achieved by use of secondary cellulosic substrates. Mixed substrate systems consisting of 5 g/L cellobiose and various Avicel concentrations (5, 10, and 16 g/L) were also studied in batch culture. The maximum cellulase activities were 53, 62, and 78 U/L, respectively. The enzyme production rate could be related to Avicel using the Monod equation. Here, maximum volumetric productivity, υ, was found to be 2.15 U/L-h and K was 7.5 g Avicel/L. Another mixed substrate system, consisting of 5 g/L cellobiose and 15 g/L Solka Floc, produced a maximum cellulase concentration of 105 U/L. [ABSTRACT FROM AUTHOR]

Large-scale production of ethanol or other transportation fuels by biological conversion of lignocellulosic biomass will eventually require integration with large-scale production of biomass substrates. The most promising candidates for efficient production of biomass in the US are short rotation hardwoods and herbaceous crops. The following samples of short rotation hardwoods were provided by the Biomass Production Program managed for the Department of Energy Biofuels and Municipal Waste Technology Division by the Oak Ridge National Laboratory: Poplar hybrid NE388 (Populus, maximowiczii x P. trichocarpa), Poplar hybrid Nil ( Populus. trichocarpa x P. deltoides), and Sweetgum (Liquidambar styraciflua). Samples of two short rotation grasses (weeping lovegrass and switchgrass) and one herbaceous legume (sericea lespedeza) were also obtained from the same source. Milled and debarked hardwoods and herbaceous samples were subjected to prehydrolysis with dilute sulfuric acid at 140 and 160 °C for reaction times ranging from 5 to 60 min. The dilute sulfuric acid hydrolyzed all hemicelluloses at longer reaction times (30-60 min at 140 °C and 5-10 min at 160 °C), but solubilized very small amounts (< 15%) of lignin and cellulose. Cellulose in all three pretreated hardwoods became highly digestible by cellulase enzyme from Trichoderma reesei. The two grasses also responded to dilute acid pretreatment very well. [ABSTRACT FROM AUTHOR]

Economic evaluations of the capital costs for anaerobic digestion systems for gas production show that the reactor is a significant cost component. The successful application of high solids digestion of processed MSW (e.g., greater than 10% solids within the digester) would allow a decrease in reactor volume with maintenance of relatively high gas production rates. However, high solids slurries do not mix well in conventional stirred tank reactors. A horizontal shaft, hydraulically driven reactor was designed and fabricated to test the anaerobic digestion of high solids concentrations. Digester performance was evaluated as a function of experimental parameters such as nutrient requirements, feeding rates, pH control, and agitator design/ rotation speed; horsepower of mixing was also evaluated for the reactor. Several startup protocols were examined to obtain a biologically stable anaerobic fermentation at high solids levels. [ABSTRACT FROM AUTHOR]

Xylan backbones in native plant cell walls are extensively acety-lated. Previously, no direct investigations as to their role in cellulolytic enzyme resistance have been done, though indirect results point to their importance. An in vitro deesterification of aspen wood and wheat straw has been completed using hydroxylamine solutions. Yields of 90% acetyl ester removal for both materials have been accomplished, with little disruption of other fractions (i.e., lignin). Apparently, as the xylan becomes increasingly deacetylated, it becomes 5-7 times more digestible. This renders the cellulose fraction more accessible, and 2-3 times more digestible. This effect levels off near an acetyl removal of 75%, where other resistances become limiting. [ABSTRACT FROM AUTHOR]

Considerable controversy exists concerning the role lignin plays in the adsorption of cellulase enzymes on biomass. Recent studies using extracted, purified hardwood lignin have shown these materials have a propensity for cellulase adsorption; however, native lignin is carbohydrate-linked and far less condensed. In this study, we report the results of adsorption-kinetics analyses of cellulase-complex activities using five pretreated aspen substrates, including an exhaustively enzyme-hydrolyzed one. These data indicate that the polymer-binding cellulase activities are removed from solution at higher rates and extents in the presence of low lignin-content versus high lignin-content substrates. This order of adsorption was found to be essentially the inverse for beta-glucosidase adsorption. [ABSTRACT FROM AUTHOR]

A preliminary process design for dilute sulfuric acid pretreatment of aspen wood chips in order to obtain fermentable sugars has been prepared and subjected to an economic evaluation. The process design was prepared according to experimental data on the kinetics of dilute sulfuric acid prehydrolysis and particle size effects obtained in this study and our previous work. The initial economic evaluation shows woodchips are 56% of the cost of production, whereas the reactor is only 4%, and the comminution operation is just under 10%, indicating that the process economics are extremely vulnerable to feedstock costs and are thus yield-sensitive. Although chances for major cost improvements by modification of the reactor design and finding alternatives to dry milling of aspen chips to small (20-80 mesh) particles needed for acid penetration and enzymatic saccharification are not great, design improvements of the process will necessitate development of a cheaper acid resistant pretreatment reactor and a less energy intensive comminution system. Experimental results on effects of particle size on the dilute acid pretreatment design are presented. [ABSTRACT FROM AUTHOR]

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Copyright of Zeitschrift für Physik is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Zeitschrift für Physik is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Zeitschrift für Physik is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Zeitschrift für Physik is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)