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1.
Experimental results are presented for continuous conversion of pretreated hardwood flour to ethanol. A simultaneous saccharification
and fermentation (SSF) system comprised ofTrichoderma reesei cellulase supplemented with additional β-glucosidase and fermentation bySaccharomyces cerevisiae was used for most experiments, with data also presented for a direct microbial conversion (DMC) system comprised ofClostridium thermocellum. Using a batch SSF system, dilute acid pretreatment of mixed hardwood at short residence time(10 s, 220°C, 1% H2SO4) was compared to poplar wood pretreated at longer residence time (20 min, 160°C, 0.45% H2SO4). The short residence time pretreatment resulted in a somewhat (10–20%) more reactive substrate, with the reactivity difference
particularly notable at low enzyme loadings and/or low agitation. Based on a preliminary screening, inhibition of SSF by byproducts
of short residence time pretreatment was measurable, but minor. Both SSF and DMC were carried out successfully in well-mixed
continuous systems, with steady-state data obtained at residence times of 0.58–3 d for SSF as well as 0.5 and 0.75 d for DMC.
The SSF system achieved substrate conversions varying from 31% at a 0.58-d residence time to 86% at a 2-d residence time.
At comparable substrate concentrations (4–5 g/l) and residence times (0.5–0.58 d), substrate conversion in the DMC system
(77%) was significantly higher than that in the SSF system (31%). Our results suggest that the substrate conversion in SSF
carried out in CSTR is relatively insensitive to enzyme loading in the range 7–25 U/g cellulose and to substrate concentration
in the range of 5–60 g/L cellulose in the feed. 相似文献
2.
Cortez Ely V. Pessoa Adalberto Assis Adilson N. 《Applied biochemistry and biotechnology》1998,(1):661-666
Xylans are the major components of the hemicellulosic fraction of lignocellulosic biomass and their hydrolysis can be obtained
using xylanases fromPenicillium janthinellum. In this work, sugarcane bagasse hemicellulosic hydrolysate was used as the substrate for producing xylanase. The precipitation
of these enzymes was studied using ethanol and Na2SO4 as precipitating agents. Ethanol precipitation experiments were performed batchwise in concentrations ranging from 10 to
80%, pH 4.0 to 7.0, at 4áC. The concentrations used in the precipitations with Na2SO4 were from 5 to 60% at pH 5.5 and 25áC. Solubility curves as a function of xylanase activity and total protein for both precipitating
agents were made. According to the results, Na2SO4 is not appropriate for precipitating xylanases in this medium since at salt concentrations higher than 25%, the enzyme was
denaturated and at this concentration less than 80% of the enzyme and total protein were precipitated. Because of differences
in xylanase and total protein solubility, a fractionated precipitation using ethanol can be performed, since with 40% ethanol,
49% of the total protein was precipitated and more than 95% of the enzyme was kept in solution. On the other hand approx 100%
of the xylanases were recovered by precipitation after adding 80% ethanol. 相似文献
3.
John D. Wright Charles E. Wyman Karel Grohmann 《Applied biochemistry and biotechnology》1988,18(1):75-90
Simultaneous saccharification and fermentation (SSF) processes for producing ethanol from lignocellulose are capable of improved
hydrolysis rates, yields, and product concentrations compared to separate hydrolysis and fermentation (SHF) systems, because
the continuous removal of the sugars by the yeasts reduces the end-product inhibition of the enzyme complex. Recent experiments
using Genencor 150L cellulase and mixed yeast cultures have produced yields and concentrations of ethanol from cellulose of
80% and 4.5%, respectively. The mixed culture was employed because B.clausenii has the ability to ferment cellobiose (further reducing end-product inhibition), while the brewing yeastS. cerevisiae provides a robust ability to ferment the monomeric sugars. These experimental results are combined with a process model to
evaluate the economics of the process and to investigate the effect of alternative processes, conditions, and organisms. 相似文献
4.
Nonisothermal simultaneous saccharification and fermentation for direct conversion of lignocellulosic biomass to ethanol 总被引:1,自引:0,他引:1
The enzymatic reaction in the simultaneous saccharification and fermentation (SSF) is operated at a temperature much lower
than its optimum level. This forces the enzyme activity to be far below its potential, consequently raising the enzyme requirement.
To alleviate this problem, a nonisothermal simultaneous saccharification and fermentation process (NSSF) was investigated.
The NSSF is devised so that saccharification and fermentation occur simultaneously, yet in two separate reactors that are
maintained at different temperatures. Lignocellulosic biomass is retained inside a column reactor and hydrolyzed at the optimum
temperature for the enzymatic reaction (50°C). The effluent from the column reactor is recirculated through a fermenter, which
runs at its optimum temperature (20-30°C). The cellulase enzyme activity is increased by a factor of 2-3 when the hydrolysis
temperature is raised from 30 to 50°C. The NSSF process has improved the enzymatic reaction in the SSF to the extent that
it reduces the overall enzyme requirement by 30-40%. The effect of temperature on β-glucosidase activity was the most significant
among the individual cellulase compounds. Both ethanol yield and productivity in the NSSF are substantially higher than those
in the SSF at the enzyme loading of 5 IFPU/g glucan. With 10 IFPU/g glucan, improvement in productivity was more discernible
for the NSSF. The terminal yield attainable in 4 d with the SSF was reachable in 40 h with the NSSF. 相似文献
5.
Ballesteros I. Oliva J. M. Ballesteros M. Carrasco J. 《Applied biochemistry and biotechnology》1993,(1):201-211
Different treatments to improve the thermotolerance of fermenting yeasts for simultaneous ethanol saccharification and fermentation
process of cellulosic materials have been examined. Yeasts of the generaSaccharomyces andKluyveromyces were tested for growth and fermentation at progressively higher temperatures in the range of 42–47°C. The best results were
obtained withK. marxianus LG, which was then submitted to different treatments in order to achieve thermotolerant clones. A total of 35 new clones
were obtained that dramatically improved the SSF of 10% Solka-floc substrate at 45°C when compared to the original strain,
some with ethanol concentrations as high as 33 g/L. 相似文献
6.
The operational characterization of a fluidized-bed bioreactor for ethanol fermentation using Ca-alginate immobilized yeast
cells is described. An additional air stream is supplied to the fermenter to ensure and maintain satisfactory fluidization
behavior of beads and to avoid slug formation. The influence of physical properties such as bead density and liquid density
on the fluidization quality and stability are discussed. 相似文献
7.
Ballesteros I. Ballesteros M. CabaÑas A. Carrasco J. MartÍn C. Negro M. J. Saez F. Saez R. 《Applied biochemistry and biotechnology》1991,(1):307-315
A total of 27 yeast strains belonging to the groupsCandida, Saccharomyces, andKluyveromyces were screened for their ability to grow and ferment glucose at temperatures ranging 32-45°C.
K. marxianus andK. fragilis were found to be the best ethanol producing organisms at the higher temperature tested and, so, were selected for subsequent
simultaneous saccharification and fermentation (SSF) studies. 相似文献
8.
Donnelly Mark I. Millard Cynthia Sanville Clark David P. Chen Michael J. Rathke Jerome W. 《Applied biochemistry and biotechnology》1998,(1):187-198
Escherichia coli strain NZN111, which is unable to grow fermentatively because of insertional inactivation of the genes encoding pyruvate:
formate lyase and the fermentative lactate dehydrogenase, gave rise spontaneously to a chromosomal mutation that restored
its ability to ferment glucose. The mutant strain, named AFP111, fermented glucose more slowly than did its wild-type ancestor,
strain W1485, and generated a very different spectrum of products. AFP111 produced succinic acid, acetic acid, and ethanol
in proportions of approx 2:1:1. Calculations of carbon and electron balances accounted fully for the observed products; 1
mol of glucose was converted to 1 mol of succinic acid and 0.5 mol each of acetic acid and ethanol. The data support the emergence
in E.coli of a novel succinic acid:acetic acid:ethanol fermentation pathway. 相似文献
9.
Hinman Norman D. Wright John D. Hogland William Wyman Charles E. 《Applied biochemistry and biotechnology》1989,(1):391-401
The economic impact of conversion of xylose to ethanol for a wood-to-ethanol plant was examined, and the maximum potential
reduction in the price of ethanol from utilization of xylose is estimated to be 0.42 per gallon from a base case price of0.42 per gallon from a base case price of
1.65. The sensitivity of the price of ethanol to the yield, ethanol concentration and rate of the xylose fermentation was
also examined, and the price of ethanol is most affected by changes in yield and ethanol concentration, with rate of lesser
importance. Current performances of various xylose conversion biocatalysts were analyzed, andC. shehatae andP. stipitis appear to be the best yeasts. 相似文献
10.
Ballesteros I. Oliva J. M. Carrasco J. Cabañas A. Navarro A. A. Ballesteros M. 《Applied biochemistry and biotechnology》1998,(1):369-381
In this work, the effect of the addition of different concentrations of Tween-80 and three different zeolite-like products
on enzymatic hydrolysis, ethanol fermentation, and simultaneous saccharification and fermentation (SSF) process has been investigated.
The ability of these products to enhance the effectiveness of the SSF process to ethanol of steam-exploded poplar biomass
using the thermotolerant strainKluyveromyces marxianus EMS-26 has been tested.
Tween-80 (0.4 g/L) increased enzymatic hydrolysis yield by 20% when compared to results obtained in hydrolysis in absence
of the additive. Zeolite-like products (ZESEP-56 and ZECER-56) (2.5 g/L) improved rates of conversion and ethanol yields in
the fermentation of liquid fraction recovered from steam-exploded poplar. The periods required for the completion of fermentation
were approx 10 h in the presence of zeolite-like products and 24 h in the absence of additives. The probable mode of action
is through lowered levels of inhibitory substances because of adsorption by the additive. 相似文献
11.
Beker M. J. Shvinka J. E. Pankova L. M. Laivenieks M. G. Mezhbarde I. N. 《Applied biochemistry and biotechnology》1990,(1):265-274
Two biotechnological systems were developed for sucrose conversion into levan and ethanol withZymomonas mobilis, ensuring a 66.7% transfer of substrate carbon in a batch and 61% carbon transfer in a continuous culture. The effect of
glucose, ethanol, and medium pH on sucrose conversion byZ. mobilis was studied. The addition of ethanol to the fermentation medium, in the final conc. of 100 g/L, uncoupled levan synthesis
from ethanol fermentation. For a continuous culture, the most efficient conversion of substrate carbon into levan was reached
at pH 4.8, giving 64.2 g/L levan, with the levan yield of 0.22 g/g and the productivity of 3.2 g/L/h. 相似文献
12.
Saha Badal C. Dien Bruce S. Bothast Rodney J. 《Applied biochemistry and biotechnology》1998,(1):115-125
Corn fiber, which consists of about 20% starch, 14% cellulose, and 35% hemicellulose, has the potential to serve as a low
cost feedstock for production of fuel ethanol. Currently, the use of corn fiber to produce fuel ethanol faces significant
technical and economic challenges. Its success depends largely on the development of environmentally friendly pretreatment
procedures, highly effective enzyme systems for conversion of pretreated corn fiber to fermentable sugars, and efficient microorganisms
to convert multiple sugars to ethanol. Several promising pretreatment and enzymatic processes for conversion of corn fiber
cellulose, hemicellulose, and remaining starch to fermentable sugars were evaluated. These hydrolyzates were then examined
for ethanol production in bioreactors, using genetically modified bacteria and yeast. Several novel enzymes were also developed
for use in pretreated corn fiber saccharification.
Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard
of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also
be suitable. 相似文献
13.
In this paper a heterogeneous model is developed for the alcoholic fermentation process. The model is expressed in terms of
intracellular and extracellular concentrations of ethanol and sugar as well as biomass concentration as state variables. The
model takes into consideration the floc size and the mass transfer rates of both ethanol and sugar. The intrinsic kinetics
of the process used in the model was developed from published data which includes the inhibitory effects of ethanol and cells.
The model development is achieved through comparison with one set of experimental results given by Novak et al. (1). The model is then checked against two other sets of experimental results. The developed model is also used to simulate
an industrial fed-batch fermentar. 相似文献
14.
15.
The cybernetic approach to modeling of microbial kinetics in a mixedsubstrate environment has been used in this work for the
fermentative production of ethanol from cheese whey. In this system, the cells grow on multiple substrates and generate metabolic
energy during product formation. This article deals with the development of a mathematical model in which the concept of cell
maintenance was modified in light of the specific nature of product formation. Continuous culture data for anaerobic production
of ethanol byKluyveromyces marxianus CBS 397 on glucose and lactose were used to estimate the kinetic parameters for subsequent use in predicting the behavior
of microbial growth and product formation in new situations. 相似文献
16.
The aim of preclarification is to minimize sludge going to yeast separators. This purpose is partially fulfilled. However,
it has been measured during the plant trial runs that preclarification does not noticeably improve fermentation.
The aim of postclarification is to minimize sludge going to distillation. This purpose is well served as noted from the fact
that cycle run of distillation columns using postclarification is three times longer (9–12 mo) as compared to the normal one
(3–4 mo). 相似文献
17.
In this technoeconomic evaluation of the manufacture of acetic acid by fermentation, the use of the bacterium:Acetobacter suboxydans from the old vinegar process was compared with expected performance of the newerClostridium thermoaceticum bacterium. Both systems were projected to operate as immobilized cells in a continuous, fluidized bed bioreactor, using solvent
extraction to recover the product.
Acetobacter metabolizes ethanol aerobically to produce acid at 100 g/L in a low pH medium. This ensures that the product is in the form
of a concentrated extractable free acid, rather than as an unextractable salt. Unfortunately, yields from glucose by way of
the ethanol fermentation are poor, but near the biological limits of the organisms involved. 相似文献
18.
19.
Keller Fcred A. Bates Delicia Ruiz Ray Nguyen Quang 《Applied biochemistry and biotechnology》1998,(1):137-148
Several strains and genera of yeast, includingSaccharomyces cerevisiae D5A,Pachysolen tannophilus, S. cerevisiae K-l,Brettanomyces custersii, Candida shehatae, andCandida acidothermophilum, are screened for growth on dilute acid-pretreated softwood prehydrolysate. Selected softwood species found in forest underbrush
of the western United States, which contain predominantly hexosan hemicellulose, were studied. This phase of the work emphasized
debarked Douglas fir. The two best initial isolates were gradually selected for improved growth by adaptation to increasing
prehydrolysate concentrations in batch culture, with due consideration of nutrient requirements. Microaerophilic conditions
were evaluated to encourage tolerance of pretreatment hydrolysate, as well as ethanol product. Adaptation and simultaneous
saccharification and fermentation (SSF) results are used to illustrate improved performance with an adapted strain, compared
to the wild type. 相似文献
20.
Schmidt Sherry L. Myers Michele D. Kelley Stephen S. McMillan James D. Padukone Nandan 《Applied biochemistry and biotechnology》1997,(1):469-482
The use of membrane processes for the recovery of fermentation products has been gaining increased acceptance in recent years.
Pervaporation has been studied in the past as a process for simultaneous fermentation and recovery of volatile products such
as ethanol and butanol. However, membrane fouling and low permeate fluxes have imposed limitations on the effectiveness of
the process. In this study, we characterize the performance of a substituted polyacetylene membrane, poly[(l-trimethylsilyl)-l-propyne]
(PTMSP), in the recovery of ethanol from aqueous mixtures and fermentation broths. Pervaporation using PTMSP membranes shows
a distinct advantage over conventional poly(dimethyl siloxane) (PDMS) membranes in ethanol removal. The flux with PTMSP is
about threefold higher and the concentration factor is about twofold higher than the corresponding performance achieved with
PDMS under similar conditions. The performance of PTMSP with fermentation broths shows a reduction in both flux and concentration
factor relative to ethanol-water mixtures. However, the PTMSP membranes indicate initial promise of increased fouling resistance
in operation with cell-containing fermentation broths. 相似文献