摘要:

AbstractFermentation of lignocellulose hydrolysates as spent sulfite liquor or as hydrolysate from sulfur‐dioxide‐treated wood to ethanol has been controlled by using biosensors for glucose and ethanol. Yield and productivity were studied with respect to concentration level of the metabolites in a continuous hollow‐fiber reactor. High constant yield was achieved by controlling the glucose to low concentration levels. Reduced productivity were obtained when fermenting at high ethanol concentrations as an effect of inhibition of the yeast cells. The observations emphasize the advantage of controlling the process to favorable concentrations of monosaccharides and et

ISSN:0006-3592    

DOI:10.1002/bit.260320202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThis work shows that the enzyme membrane reactor offers the opportunity to carry out the enzymatic regeneration of ATP providing continuous operation with high performance. In this system, the coenzyme is immobilized on a water‐soluble polymer. These high‐molecular weight derivates are entrapped within an ultrafiltration membrane together with the enzymes for production of regeneration. Several polymer derivatives of ATP have been prepared for this immobilization technique. Coenzymatic activity of these derivatives was studied with several enzymes for both ATP‐requiring and ATP‐regenerating reactions. PEG‐N6‐aminohexyl‐ATP was selected as the appropriate coenzyme for operating the enzyme membrane reactor. Acetate kinase was the only enzyme providing enough activity for regeneration. Production of glucose‐6‐phosphate is cited as the first example. The kinetics of acetate kinase and hexokinase were examined and used to choose the operating conditions of the process. The process operated continuously for more than 1 month. With a mean conversion of 80%, the space–time yield amounted to 348 g glucose‐6‐phosphate/L d. The cycle number of ATP was estimated as 20, 000 mol/mol. With the continuous production of γ‐glutamylcysteine and NADP, the feasibilit

ISSN:0006-3592    

DOI:10.1002/bit.260320203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe marine diatomCyclotella crypticawas grown over a period of 13 months in a 48‐m2shallow outdoor flume. The use of foil arrays at intervals of 1.2 m to effect systematic vertical mixing in the flume was found to significantly enhance microalgal production (p= 0.006). Average photosynthetic efficiencies (based on visible irradiance) with and without the foil arrays in place were 9.6 ± 0.8 and 7.5 ± 0.5% (±95% confidence intervals), respectively. A cost–benefit analysis indicated that the foil arrays were cost‐effective if the value of the algae exceeded about $2.28 kg1of ash‐free dry weight (AFDW). Parallel experiments performed in four 9.2‐m2flumes showed that production was maximized when the cells were grown on a 2‐day batch cycle between harvests rather than on a 1‐ or 3‐day batch cycle. The optimum initial concentration (immediately after harvesting) of the algae was negatively correlated with the time interval between harvests and ranged from approximately 39 g AFDW/m3on a 3‐day cycle to 213 g AFDW/m3on a 1‐day cycle. The increase in production resulting from growth on a 2‐day rather than a 1‐day batch cycle was about 19% and was statistically significant atp= 0.0003. Growth ofC. crypticaover a total period of 122 days during the 13‐month study in the 48‐m2flume under near‐optimal conditions (2‐day batch cycle, initial concentration 155 g AFDW/m3) resulted in an average production rate (±95% confidence

ISSN:0006-3592    

DOI:10.1002/bit.260320204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractAlcohol dehydrogenase from horse liver was immobilized by covalent attachment to CNBr‐Sepharose and by adsorption to octyl‐Sepharose CL‐4B, a hydrophobic analog of Sepharose. In each case, rate constants for the binding and release of coenzyme and for the oxidation of substrates were measured based on the concentration of accessible active‐site zinc atoms determined by titration with a paramagnetic inhibitor. All rate constants were substantially reduced upon immobilization; however, the rate constant of immobilized enzyme for ethanol oxidation was independent of the immobilization method, whereas the rate constant for cyclohexanol oxidation was lower for enzyme immobilized to octyl‐Sepharose. Consequently, the substrate specificity of the two immobilized enzyme samples differed by an order of magnitude. Moreover, EPR spectroscopy studies and computer graphic analyses of spin labels occupying three defined regions of the active‐site domain indicated that the active‐site conformation adjacent to the catalytic zinc atom was similar in the two samples while the conformation slightly further from the zinc atom was different. This result may explain why the two immobilized enzyme preparations exhibited the same rate constant toward a small substrate (ethanol) yet different rate constants toward a larger substrate (cyclohexanol), whose rate constant is expected to be sensitive to a larger portion of th

ISSN:0006-3592    

DOI:10.1002/bit.260320205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractAnaerobic degradation performance of a laboratory‐scale packed‐bed reactor (PBR) was compared with two fluidized‐bed biofilm reactors (FBRs) on molasses and whey feeds. The reactors were operated under constant pH (7) and temperature (35°C) conditions and were well mixed with high recirculation rates. The measured variables were chemical oxygen demand (COD), individual organic acids, gas composition, and gas rates. As carrier, sand of 0.3–0.5 mm diameter was used in the FBR, and porous clay spheres of 6 mm diameter were used in the PBR. Startup of the PBR was achieved with 1–5 day residence times. Start‐up of the FBR was only successful if liquid residence times were held low at 2–3 h. COD degradations of 86% with molasses (90% was biodegradable) were reached in both the FBR and PBR at 6 h residence time and loadings of 10 g COD/L day. At higher loadings the FBR gave the best performance; even at 40–45 g COD/L day, with 6 h residence times, 70% COD was degraded. The PBR could not be operated above 20 g COD/L day without clogging. A comparison of the reaction rates show that the PBR and FBR per formed similarly at low concentrations in the reactors up to 1 g COD/L, while above 3 g COD/L the rates were 17.4 g COD/L day for the PBR and 38.4 g COD/L day for the FBR. This difference is probably due to diffusion limitations and a less active biomass content of the PBR compared with the fluidized bed.The results of dynamic step change experiments, in which residence times and feed concentrations were changed hanged at constant loading, demonstrated the rapid response of the reactors. Thus, the response times for an increase in gas rate or an increase in organic acids due to an increase in feed concentration were less than 1 day and could be explained by substrate limitation. Other slower responses were observed in which the reactor culture adapted over periods of 5–10 days; these were apparently growth related. An increase in loading of over 100% always resulted in large increases inorganic acids, especially acetic and propionic, as well as large increases in the CO2gas content. In general, the CO2content of the gas was very low, due to the large amount of dissolved CO2that exited with the liquid phase at low residence times. The performance of the FBR with whey was comparable to its performance with molasses, and switching of molasses to whey feed resulted in immediate good performance

ISSN:0006-3592    

DOI:10.1002/bit.260320206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractBatch foam separation has been employed to separateSaccharomyces carlsbergensiscells from their broth without the use of any external surface‐active agent. A model has been developed to predict the foamate cell concentration as well as the variation of cell concentration in the bulk liquid in the foam column as a function of time. The model assumes a linear equilibrium relation between the cell concentrations at the interface and the bulk. The foam has interface as well as interstitial liquid. The interface is assumed to be in equilibrium with the interstitial liquid, which in turn is assumed to have the same concentration as the bulk. The interfacial area is calculated by assuming the foam bubbles to be pentagonal dodecahedral in shape. The model has been found to explain the results of foam separation of cells quite well, particularly with respect to the effect of bubble size and aeration rat

ISSN:0006-3592    

DOI:10.1002/bit.260320207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractA new combined bioreactor‐separator system was designed and its operational feasibility demonstrated in order to develop a bioprocess that enables us to handle simultaneous biotransformation and recovery of product by crystallization. Enzymatic conversion ofL‐aspartate toL‐alanine byL‐aspartate β‐decarboxylase fromPseudomonas dacunhae(ATCC 21192) was used as a model system for this study to demonstrate the principles involved in the bioprocess design. Immobilized cells ofP. dacunhaecontaining the enzyme were fluidized in a tapered column type of bioreactor and a filter‐crystallizer combination was used as a separator unit in our experimental system.It was found that almost a theoretical yield was achieved, and the process control for both the bioreactor operation and separation was relatively easy. The Production systems, namely, the recirculating bioreactor separator combination system and the conventional batch reactor system, were analyzed and compared based on the results obtained form this study, and it was found that a significant cost reduction, by about 20%, can be achieved when the recirculating bioreactor–separator combination system was employed. Based on these findings, it is anticipated that the conceptual design of the bioreactor–separator combination system evaluated in this study has some potential for indust

ISSN:0006-3592    

DOI:10.1002/bit.260320208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe performance of differential contactors for use in extractive fermentation is complicated by the effects of product formation in the contactor. When product formation is significant, approximate analytical solutions are presented for the performance of the contactor for two limiting cases: high and low substrate concentrations. When products are formed at a constant rate, there is a minimum raffinate solute concentration that can be obtained, in contrast to the behavior of a column in the absence of product formation. General equations describing the behavior of the system for product formation with backmixing in both phases are presented. The case of a stripping factor not equal to unity is considered.

ISSN:0006-3592    

DOI:10.1002/bit.260320209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractAspergillus nigerB60 was immobilized in a dual hollow‐fiber bioreactor (DHFBR) to produce citric acid continuously. The fungi proliferated well in the interstitial region formed by a parallel arrangement of three microporous polypropylene hollow fibers contained within a silicone tube. Long‐term operation with nitrogen‐enriched medium was not possible due to expansion of the silicone tubes by continual cell growth. The fungal growth could be controlled by supplying a nitrogen‐deficient medium at the production stage. With pure oxygen aeration and nitrogen‐deficient medium, volumetric productivity reached 1.62 g/L h at a residence time of 4.02 h, which corresponded to a 27‐fold increase over that of shake‐flask fermentation. When the residence time was increased to 20.1 h, citric acid at a concentration of 26 g/L was continuously produced, with a yield of 80‐90% and a volumetric productivity of 1.3 g/L h. This represents a significant improvement in final concentration, yield, and the volumetric productivity over the equivalent values of the corresponding batch fermentation, which were 18 g/L, 40%, and 0.06 g/L

ISSN:0006-3592    

DOI:10.1002/bit.260320210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractLactate dehydrogenase (LDH) was covalently attached to an impervious nylon surface by an improved technique. The procedure allowed the kinetics of the rotating enzyme disk reactor to be successfully explored. This enzyme‐disk configuration has potential applications in assays for lactic acid or pyruvic acid in fluids of biological importance (e.g., urine). In order to evaluate and understand the physics and chemistry underlying the kinetics of the heterogeneous biocatalyst, a mathematical model based on the von Karman‐Levich theories of rotating electrodes, was developed. It applied well to LDH attached to a disk, under variable NADH concentrations and fixed pyruvic acid. The new theory, leads to the conclusion that the apparent Michaelis constantKm(app), varies linearly withf‐1/2, wherefis the speed of rotation of the disk. Extrapolation off‐1/2to zero gives the Michaelis‐Menten constant,Km, corresponding to the diffusion‐free behavior. With immobilized LDH, the diffusion‐freeKmfor NADH obtained at 25°C, in phosphate buffer (pH 7.5) using the extrapolation method was 84 μM. This value was in good agreement with the previously published value of 87 μM, obtained with LDH attached to the inner surface of a nylon tubing. However, when compared to theKmfor a free enzyme system, the 84 μM was about nine times larger, indicating an inherent reduction in the activity of the bound LDH. Since, at extrapolated infinite rotation speeds, diffusion effects were assumed eliminated, the drop in the activity was thought to be due to sterric hinderances imposed on the substrate NADH as a result of having LDH bound t

ISSN:0006-3592    

DOI:10.1002/bit.260320211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY