bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristics of carbohydrate degradation and the rate‐limiting step in anaerobic digestion
Authors: Noike Tatsuya , Endo Ginro , Chang Juu‐En , Yaguchi Jun‐Ichi , Matsumoto Jun‐Ichiro 
Published: December 2004

AbstractThe characteristics of the degradation of cellulose, soluble starch, and glucose in the acidogenic phase and the effects of the substrate loading rate and biological solids retention time on the methanogenic phase of anaerobic digestion were investigated. The results obtained from continuous experiments using laboratory‐scale anaerobic chemostat reactors elucidated the true rate‐limiting step of anaerobic digestion. The specific rate of substrate utilization decreased in the following order: glucose, soluble starch, acetic acid, and cellulose. The rate of the hydrolysis of cellulose was so low that this was shown to be the rate‐limiting step in overall anaerobic digestion. Among methanogenic bacteria Methanosarcina would provide a higher substrate utilization rate than Methanothrix, and the maximum allowable substrate loading rate in the methanogenic phase was 11.2 g acetic acid/L day.
Relationship between the fine structure of native cellulose and cellulose degradability by the cellulase complexes of Trichoderma reesei and Clostridium thermocellum
Authors: Weimer Paul J. , Weston Wayde M. 
Published: December 2004

AbstractThe initial rate of hydrolysis of six commercially available native (type l) celluloses was determined for the crude cellulase complexes of the thermophilic anaerobic bacterium C. thermocellum and the mesophilic fungus T. reesei. These rates were then compared with certain physical features of the substrates in an attempt to determine the role of cellulose structure in its degradability. Within the substrate series tested, the Clostridium system showed a greater relative range in rate of enzymatic hydrolysis than did the Trichoderma system. Average correlation coefficients for the kinetic rates from bacterial and fungal cellulases, respectively, and the following physical parameters were obtained: relative crystallinity index (RCl) from acid hydrolysis, −0.61 and −0.85; RCl from x‐ray diffraction, −0.75 and −0.89; accessibility to formylation at 4°C, + 0.49 and +0.60; nonaccessibility to formylation at 65°C, −0.40 and −0.73; fiber saturation point, + 0.83 and + 0.85. Kinetic and pore volume distribution data suggest that the rate‐limiting components of both the bacterial and fungal cellulase systems are of similar size, approximately 43 Å along one axis.
Utilization rates of trace halogenated organic compounds in acetate‐grown biofilms
Authors: Bouwer Edward J. , McCarty Perry L. 
Published: December 2004

AbstractTrace concentrations of chlorinated benzenes and chlorinated aliphatics were biotransformed by acetate‐supported biofilms, the former under aerobic conditions and the latter under methanogenic conditions. The rates of transformation of the halogenated organic compounds (secondary substrates) differed from that of acetate, the primary substrate; some were higher, some were lower, and some were similar. Factors affecting the relative rates of utilization in multisubstrate systems are not known.
A kinetic model for product formation in unstable recombinant populations
Authors: Lee Sun Bok , Seressiotis Alex , Bailey James E. 
Published: December 2004

AbstractA mathematical model has been formulated for product formation by unstable recombinant organisms in batch and in continuous flow reactors. The cell population is characterized by three different genotypes according to the absence or presence of plasmids (segregational instability) and of active cloned gene (structural instability). Empirical growth inhibition factors due to plasmids and to product protein are assigned to the corresponding strains. Product formation kinetics are based upon a quasi‐steady‐state transcription–translation expression model. An approximate form of these mechanism‐based product formation kinetics is identical to the traditional, empirically based Leudeking–Piret formula. Alternative models which consider inhibition based on overall product concentration and based on intracellular product concentration are posed, and their implications are compared. Simulation results based on these models indicate (1) overall plasmid stability depends on product expression and reactor operating conditions as well as on intrinsic segregation and mutation rate parameters; (2) there exists an optimum combination of plasmid copy number and cloned‐gene transcription and translation efficiencies to maximize reactor productivity; and (3) continuous reactor dilution rate influences the fraction of productive cells. General trends and substrate, product, and cell concentration time trajectories obtained from model simulation agree well qualitatively with currently available experimental information.
Effect of shear on membrane‐associated enzymes: Studies of the release of intracellular protein and of the progesterone 11α‐hydroxylase complex from rhizopus nigricans
Authors: Talboys B. L. , Dunnill P. 
Published: December 2004

AbstractRhizopus nigricans ATCC 6227b grown in either shake flasks or a fermentor was sheared in a concentric cylinder viscometer. The cells grown in shake flasks were found to be more susceptible to disruption by shear than those grown in the fermentor. Cells resuspended in a medium containing reduced glutathione and EDTA were found to be more easily disrupted than cells resuspended in 0.5% NaCl. The optimum condition for disruption of shake flask cells grown in the former medium with retention of progesterone 11α‐hydroxylase activity was a laminar shear rate of 4300 s−1, for a period of 3 min at 4°C. During the first 30 s the apparent viscosity was found to decrease significantly with applied shear.
Grain sorghum stillage recycling: Effect on ethanol yield and stillage quality
Authors: Egg Richard P. , Sweeten John M. , Coble Charlie G. 
Published: December 2004

AbstractStillage obtained from ethanol production of grain sorghum was separated into two fractions: thin stillage and wet solids. A portion of the thin stillage was recycled as cooking water in subsequent fermentation runs using both bench‐ and full‐scale ethanol production plants. When thin stillage replaced 50–75% of the cooking water, large increases occurred in solids content, COD, and EC of the resulting thin stillage. It was found that while the volume of thin stillage requiring treatment or disposal was reduced, there was little reduction in the total pollutant load. Stillage rcycling had little effect on the quality of the stillage wet solids fraction. At the high levels of stillage recycle used, ethanol yield was reduced after three to five runs of consecutive recycling.
Extraction chemistry of fermentation product carboxylic acids
Authors: Kertes A. S. , King C. J. 
Published: December 2004

AbstractWithin the framework of a program aiming to improve the existing extractive recovery technology of fermentation products, the state of the art is critically reviewed. The acids under consideration are propionic, lactic, pyruvic, succinic, fumaric, maleic, malic, itaconic, tartaric, citric, and isocitric, all obtained by the aerobic fermentation of glucose via the glycolytic pathway and glyoxylate bypass. With no exception, it is the undissociated monomeric acid that is extracted into carbon‐bonded and phosphorus‐bonded oxygen donor extractants. In the organic phase, the acids are usually dimerized. The extractive transfer process obeys the Nernst law, and the measured partition coefficients range from about 0.003 for aliphatic hydrocarbons to about 2 to 3 for aliphatic alcohols and ketones to about 10 or more for organophosphates. Equally high distribution ratios are measured when long‐chain tertiary amines are employed as extractants, forming bulky salts preferentially soluble in the organic phase.
A semicontinuous culture model that links cell growth to extracellular nutrient concentration
Authors: Quinlan Alician V. 
Published: December 2004

AbstractDuring semicontinuous culture, a sample of fixed volume is removed at regular time intervals to make measurements and/or harvest culture components, and an equal volume of fresh medium is immediately added to the culture, thereby instantaneously enhancing nutrient concentrations and diluting cell concentration. The resulting cell concentration versus time curve (i.e., the actual cell growth curve) has a saw‐toothed appearance because of the periodic dilution of cell concentration. The observed cell concentrations correspond to the peaks of the saw‐toothed curve. Cell growth rates are estimated from the locus of observed cell concentrations (i.e., from the apparent growth curve obtained by connecting the peaks of the saw‐toothed curve). The sole preexisting model (Fencl's mode) for estimating cell growth rate is valid only when the cells are growing exponentially at a constant rate between samplings. This model has limited validity: despite the periodic enhancement of nutrient concentration, cell growth between samplings eventually causes nutrient depletion, and the cells cease to grow exponentially. Failure to recognize the limits of validity for Fencl' model has resulted in many erroneous applications of the model and, consequently, many incorrect estimates of cell growth rates. To provide a means for correctly estimating cell growth rates, Fencl's exponential model was extended, and a new model that describes the effects of nutrient depletion on cell growth in semi‐continuous culture was obtained. The new model shows that exhaustion of a single growth‐limiting nutrient in semicontinuous culture causes the locus of cell concentrations observed at time intervals of Δt to follow a logistic growth curve. The actual cell growth rate was shown to equal the apparent logistic growth rate plus the effective dilution rate −Δt−1 In (1 − f), where f is the ratio of sample volume to total culture volume. Moreover, the model predicts that both the apparent logistic growth rate and the apparent steady‐state cell concentration should rise linearly with the concentration of growth‐limiting nutrient in the input medium, but fall linearly with increases in the effective dilution rate. The new logistic model for nutrient‐limited cell growth in semicontinuous culture was successfully tested using published data for Asterionella formosa, Cyclotella meneghiniana, Daucus carota, and strain L mouse cells.
Enzymatic production of L‐serine with a feedback control system for formaldehyde addition
Authors: Hsiao Humg‐Yu , Wei Tena 
Published: December 2004

AbstractSerine hydroxymethyltransferase (SHMT) in the form of crude extract from a recombinant strain of Klebsiella aerogenes was used for the production of L‐serine from glycine and formaldehyde (HCHO). A stirred tank bio‐reactor with a continuous feed of HCHO (37%) was employed. Since the performance of the serine bioreactor was heavily dependent on how HCHO was fed, an automatic feedback control system was developed for HCHO delivery utilizing the phenomenon of formol titration. This control procedure was based on the following circumstance: as a bioconversion proceeded, if the rate of HCHO feed was balanced by the rate of serine synthesis so that HCHO concentration was maintained near zero, then there was no pH change in the bioreactor. Once the rate of HCHO addition exceeded that of serine synthesis, the HCHO concentration built up and the excess HCHO reacted with the amino group of an amino acid (e.g. glycine or serine) to produce a Schiff base and a proton which lowered the pH. A pH controller detected and relayed this pH change to the on–off switch of the HCHO feed pump. Thus, HCHO infusion stopped when the pH was lower than the set point, which was the initial pH of the reaction. With this control system, the maximum concentration of HCHO that was reached in the bioreactor was only 1mM–3.3mM depending on the pH and amino acid composition in the bioreactor. Moreover, a decrease in pH also signaled the use of a slower feed rate at which HCHO was to be, delivered once the pH resumed its initial value after excess HCHO was consumed by the reaction. Employing this control system, we have optimized the performance of the serine bioreactor to give a serine titer of 450 g/L with an 88% molar conversion of glycine at a volumetric serine productivity of 8.9 g/L/h.
Saccharification of concentrated brewing bagasse slurries with dilute sulfuric acid for producing acetone–butanol by Clostridium acetobutylicum
Authors: Juanbaró Josep , Puigjaner Lluis 
Published: December 2004

AbstractA comprehensive kinetic study of the acid hydrolysis of concentrated brewing bagasse slurries was performed. The use of the simple series reaction model was found to be suitable when a “heterogeneous correction” (pseudosubstrate‐inhibition) is taken into account in slurries with low liquid‐to‐biomass ratios. Rate constants are shown to be dependent not only on temperature and acid concentration but essentially also on the initial biomass concentration. Actual rate constants, activation energies, and acid and substrate reaction orders are reported for xylan, arabinan, and α‐glucan acid saccharification. There is a threshold acid loading necessary to overcome the 80% conversion, but no threshold has been found to overcome the “neutralizing” property of cellulosic materials. Reversible acid capture from brewing bagasse has been postulated. The highest monosccharide concentration into hydrolyzates has been found (65 g/L) after 10 h treatment, but economic considerations led us to treat a mean‐concentrated slurry (156 g/L) with 0.3M H2SO4 at 96°C, thus obtaining 45.5 g/L monosaccharides in 5 h with 50% less furfural content. After pH regulation only, growth of Clostridium acetobutylicum has been obtained, although complete sugar comsumption has not been achieved. Experiments are now underway to reach complete digestion and to investigate the increase of enzymic accessibility into residual substrate rich in cellulose.
Anaerobic digestion of high‐strength cheese whey utilizing semicontinuous digesters and chemical flocculant addition
Authors: Barford J. P. , Cail R. G. , Callander I. J. , Floyd E. J. 
Published: December 2004

AbstractSemicontinuous digesters were used to anaerobically treat high‐strength whey (70 kg/m3·COD). A maximum loading of 16.1 kg COD/m3·day was obtained with soluble COD removal efficiencies greater than 99%. The use of a chemical flocculant resulted in an increased biomass concentration in the digester compared to a control, thus enabling correspondingly higher space loadings to be applied. With the onset of substantial levels of granulation of the biomass, flocculant dosage was able to be discontinued. This article discusses the performance of the digesters in detail and, briefly, the long‐term operational difficulties experienced and the control strategies employed on such systems.
Modeling the liquid flow in up‐flow anaerobic sludge blanket reactors
Authors: Bolle W. L , van Breugel J. , van Eybergen G. C. , Kossen N. W. F. , Zoetemeyer R. J. 
Published: December 2004

AbstractBy means of stimulus‐response experiments an Li+ tracer, models for the fluid flow in a 30‐m3 UASB reactor, used for the anaerobic treatment of wastewater, were tested. From the model with the best fit it could be derived that both the sludge bed and the sludge blanket can be described as perfectly mixed tank reactors with short‐circuiting flows; the settler volume acts like a plug‐flow region.Apart from the volumes of the different flow regions, two parameters are necessary and sufficient to describe the fluid flow in a well functioning UASB reactor, i.e., the short‐circuiting flow over the sludge bed and the short‐circuiting flow over the sludge blanket. The volumes could be measured accurately.The short‐circuiting flow over the sludge bed is a linear function of the sludge bed height. When the optimal height of the sludge bed is defined as the height for which the short‐circuiting flows are as small as possible, a bed‐height of 3.5–4 m is sufficient (for superficial gas velocities between 1 and 1.5 m/h). This is in contradiction to the results of other authors. The short‐circuiting flows over the sludge bed and the sludge blanket were also influenced by the superficial gas velocity.
Immobilization of Enzyme into Poly(vinyl alcohol) Membrane
Authors: Imai Kiyokazu , Shiomi Tomoo , Uchida Kozo , Miya Masamitsu 
Published: December 2004

AbstractGlucoamylase, invertase, and cellulase were entrapped within poly(vinyl alcohol) (PVA) membrane cross‐linked by means of irradiation of ultraviolet light. The conditions for immobilization of glucoamylase were examined with respect to enzyme concentration in PVA, sensitizer (sodium benzoate) concentration in PVA, irradiation time, and membrane thickness. Various characteristics of immobilized glucoamylase were evaluated. Among them, the pH activity curve for the immobilized enzyme was superior to that for the native one, and thermal stability was improved by immobilization with bovine albumin. The apparent Km was larger for immobilized glucoamylase than for the native one, while Vmax was smaller for the immobilized enzyme. Also, the apparent Km appeared to be affected by the molecular size of the substrate. Further, immobilized invertase and cellulase showed good stabilities in repeating usage.
Ethanol production from starch by a coimmobilized mixed culture system of Aspergillus awamori and Zymomonas mobilis
Authors: Tanaka Hideo , Kurosawa Hiroshi , Murakami Hiroshi 
Published: December 2004

AbstractThe production of ethanol from starch by a coimmobilized mixed culture system of aerobic and anaerobic microorganisms in Ca‐alginate gel beads was investigated. The mold Aspergillus awamori was used as an aerobic amylolytic microorganism and an anaerobic bacterium, Zymomonas mobilis, as an ethanol producer. By controlling the mixing ratio of the microorganisms in the inoculum size, a desirable coimmobilized mixed culture system, in which the aerobic mycelia grew on and near the oxygen‐rich surface of the gel beads while the anaerobic bacterial cells mainly grew in the oxygen‐deficient central part of the gel beads, was naturally established under the aerobic culture conditions, and ethanol could be directly produced from starch by the system. The ethanol productivity by the system in flask culture was particularly affected by the shear stress (dependent on the shaking speed) which controlled the mycelial growth on the surface of the gel beads. Under optimum culture conditions in the flask culture, the glucose produced was instantly consumed, and was not observed in the culture broth; the final concentration of ethanol produced from 100 g/L starch was 25 g/L and the yield coefficient for ethanol, Ypls, was 0.38. The ethanol productivity by the coimmobilized mixed culture system was compared with those by other various culture systems and the advantages of the system were clarified.
The application of a novel heat flux calorimeter for studying growth of Escherichia coli W in aerobic batch culture
Authors: Marison I. W. , von Stockar U. 
Published: December 2004

AbstractThe modification and principle of a novel heat flux calorimeter for the in situ, on‐line measurement of the heat generated during microbial growth is described. Data concerning the physical characterization of the calorimeter as a fermentor, including stability and sensitivity of the heat signal, are presented. The calorimeter has been successfully applied to the study of the aerobic batch culture of Escherichia coli W on glucose under carbon and nitrogen limitation. A direct correlation between growth and heat evolution was obtained. Quantitative analysis of the data suggests that the new calorimetric technique could be used for monitoring growth and specific metabolic events, for convenient medium optimization, and as a basis for a novel fermentation process control system.
Coimmobilization of malate dehydrogenase and formate dehydrogenase in polyethyleneglycol(#4000)diacrylate gel by droplet gel‐entrapping method
Authors: Kajiwara S. , Maeda H. 
Published: December 2004

AbstractA new immobilization technique suitable for coupled enzymes requiring cofactors was established. This is a droplet gel‐entrapping method in which many small droplets including the enzymes are fixed in the gel. The first emulsion was prepared by mixing of a solution containing thermostable malate dehydrogenase (MDH) and formate dehydrogenase (FDH) with benzene containing a surfactant. The first emulsion was added to a solution containing polyethyleneglycol(#4000)diacrylate and N,N′‐methylenebisacrylamide to prepare the second emulsion (w/o/w). After the second emulsion was gelled by addition of potassium persulfate and 3‐dimethylaminopropionitrile, the benzene was removed. The expressed MDH and FDH activities of the MDH–FDH immobilized gel were 7.1 and 13.9% of the initial activities, respectively. The Km values of the gel were 0.60mM for formate and 1.5μM for NAD, respectively. The Km for formate and NAD were found to be extremely low. By using the column packed with 30 g gel having the MDH activity of 41.7 units and the FDH activity of 11.1 units, 13.8mM oxalacetate was completely converted to malate at 30°C. The malate production rate was not affected by the concentration of more than 50mM formate, more than 2mM oxalacetate, and more than 0.1 mM NAD, respectively. Long‐term malate production was demonstrated at 30°C by passing the substrate solution containing the two substrates and NAD through the column. The maximum conversion ratio (7.8%) was obtained at the fifth day, and 83% of maximum productivity was maintained even after 3 weeks. The expressed FDH activity at the fifth day was calculated to be 20.5% of the initial activity.
A model for the filterability of activated sludge supported by mixed‐liquor biochemical data
Authors: Novak R. A. 
Published: December 2004

AbstractA predictive model was developed to estimate the dewatering characteristics of waste‐activated sludges. This model utilizes the COD‐nitrogen ratio of the wastewater and the organic loading rate of the process to predict sludge filterability in terms of specific resistance. A completely mixed, continuous flow secondary treatment process with solids recycle was used for the cultivation of activated sludges. The sludge wasted from this process was used in Buchner funnel specific resistance determinations. The basic concepts involved in the development of the model were supported by sludge carbohydrate, protein, and surface charge data.
Production of penicillin in a fluidized‐bed bioreactor using a carrier‐supported mycelial growth
Authors: Kim J. H. , Oh D. K. , Park S. K. , Park Y. H. , Wallis D. A. 
Published: December 2004

AbstractA carrier‐supported mycelial growth of Penicillium chrysogenum was applied to penicillin fermentation system using celite as a support material. Hyphal growth through the pore matrices of the material showed strong anchorages and provided highly stable biofilm growth. With bioparticles developed in such a manner, both cell growth and penicillin production were observed to increase significantly compared to the conventional dispersed filamentous cultures. Maximum values of specific penicillin production rate were found to be constant regardless of the growth form. A three‐phase fluidized‐bed fermentor was designed and tested for penicillin production using the bioparticles. Two modes of operation, semicontinuous and repeated fed batch, of the fermentor were tried. It was noted that the overgrowth of free mycelia and the development of fluffy loose bioparticles caused poor mixing and made the fermentor operation quite difficult. Control of the bioparticle size and the extension of production phase were therefore considered important to maintain the reactor productivity at a desired level. From the results of repeated fed‐batch operation it was found that the control of bioparticle size could be successfully achieved by phosphate‐limiting culture condition. Penicillin production under this condition was also observed to be maintained at a high level (about 80% of the maximum) for at least 1 month.