摘要:

AbstractMethemoglobin can be reduced on a platinum cathode using flavin mononucleotide as an oxido‐reduction mediator. The process requires the utilization of a filter‐press cell with compartments separated by a semi‐permeable membrane. Analysis of the various constraints imposed by the process itself and by the nature of the molecules involved shows that the electrolysis cell must operate at a low temperature, in strictly anaerobic conditions, in series with a storage tank, and with fluid circulation rates lower than approximately 0.8 m/s. A process has been designed that takes into account these imperatives and enables volumes of solution of the order of 200 cm3to be processed. It enables optimization of the flow rates used as well as of the methemoglobin/flavin ratio and is the forerunner of an industrial re

ISSN:0006-3592    

DOI:10.1002/bit.260360402

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

年代:1990

数据来源: WILEY

摘要:

AbstractA recombinantEscherichia coliHB101(pPAKS2) producing penicillin acylase was cultured in a membrane cell recycle fermentor. The strain was very stable throughout the whole experiment. The main inhibitory by‐product was acetic acid, and cell growth ceased when its concentration was above 14 g/L Cell density could be increased up to 145 g/L dry weight without experiencing by‐product inhibition by regulating glucose concentration in the fermentor and by using total membrane recycle. Acetic acid formation was negligible not only when cells were cultured in medium containing no glucose but also when glucose was limited. Dissolved oxygen control as well as glucose limitation was an indispensable condition for minimizing acetic acid formation when the medium contained glucose. Low concentrations of accumulated acetic acid were reused when glucose was limited. Use of highly concentrated medium reduced the membrane surface area required for cell recycle greatly. The recycle fermentor could be operated in various operational modes including partial bleed and repeated recycle culture to give high productivity. Productivity of a repeated recycle system was over 10 times higher than that of a simple batch sys

ISSN:0006-3592    

DOI:10.1002/bit.260360403

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn batch fermentationLeuconostoc mesenteroidesimmobilized in calcium alginate beads produced a total dextransucrase activity equal to about 93% of that by free, suspended bacterial cells under comparable conditions in a bubble column reactor. Continuous sucrose feeding (5 g/L h) to the immobilized‐cell culture in the airlift bioreactor increased production of enzymatic activity by about 107% compared with ordinary batch operation of this reactor. About 14% of the enzymatic activity produced by the immobilized cells appears as soluble activity in the cell‐free broth compared with about 40% in case of free cells. In an airlift bioreactor, both the soluble and the intact (sorbed and entrapped) enzymatic activity produced by the immobilized bacterial cells was about 34% greater under automatic pH control, compared to that produced in a bubble column reactor with only manual pH control. During formation of dextran by intact enzyme within cells and beads, declines are observed in apparent enzymatic activ

ISSN:0006-3592    

DOI:10.1002/bit.260360404

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

年代:1990

数据来源: WILEY

摘要:

AbstractCells ofLeuconostoc mesenteroidesimmobilized in calcium alginate beads were used to produce dextransucrase (DS) in three sequential cycles of semicontinuous fed‐batch fermentations. Each cycle consisted of a fed‐batch DS production period of 24 h followed by a batch dextran production period for another 24 h. Free, suspended cells were used in only one cycle of fed‐batch DS production followed by a dextran production period. It was impractically tedious to separate and reuse free cells. Increasing sucrose feed rate from 5 to 10 g/L h led to increases of the total enzymatic activity by about 88% with immobilized cells and by about 100% with free cells. In DS fed‐batch semicontinuous fermentation, total enzymatic activity produced by immobilized cells was 1.35 and 1.56 times greater than that produced by free cells with respective sucrose feeding rates of 10 and 5 g/L h. These increases in enzyme productivity with immobilized cells, however, required total overall operating times three times longer (three cycles) than with free cells (one cycle). Growing the microorganism at optimum conditions for DS production also increased the dextran yield and shortened the time of conversion of sucrose to dextran, regardless of whether the cells were free or immobilized. Moreover, during three cycles of semicontinuous operation (144 h) immobilized cells produced more than three times as much dextran as free cells during one cycle

ISSN:0006-3592    

DOI:10.1002/bit.260360405

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

年代:1990

数据来源: WILEY

摘要:

AbstractA biochemical engineering framework for optimizing the design and operation of fractional protein precipitation has been developed. The method utilizes a fractionation diagram to represent the purification of a product protein relative to total contaminating protein. The purification factor for a single or double‐cut fractional precipitation is obtained as the gradient of an appropriate operating tie‐line. A computer algorithm has been devised to maximize the tie‐line gradient for a given yield enabling a plot of optimum purification factor versus yield to be constructed. The recovery of the enzyme alcohol dehydrogenase from clarified bakers homogenate using saturated ammonium sulphate has been examined. Fractionation and purification versus yield diagrams were used to investigate the effects of such process parameters as pH, temperature, and initial total protein concentration on fractionation efficiency. The results are discussed in terms of the underlying solubility and mixing phenomena and the industrial application of fractional precipit

ISSN:0006-3592    

DOI:10.1002/bit.260360406

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

年代:1990

数据来源: WILEY

摘要:

AbstractFor the application of immobilized enzymes, fixed bed reactors are used almost exclusively. Fixed bed reactors have specific disadvantages, especially for processes with a deactivating catalyst. Therefore, we have studied a novel reactor type with continuous transport of the immobilized biocatalyst. Flow of biocatalyst is countercurrent to the substrate solution. Because of a stagewise reactor design, back‐mixing of biocatalyst is very limited and transport is nearly plug flow. The reactor operates at a constant flow rate and conversion, due to constant holdup of catalytic activity. The reactor performance is compared with a configuration of fixed bed reactors. For reactions in the first‐order regime, enzyme requirements in this new reactor are slightly less than for fixed bed processes. The multistage fluidized bed appears to be an attractive reactor design to use biocatalyst to a low residual activity. However, nonuniformity of the particles might affect plug flow transport of the biocatalyst. A laboratory scale reactor and experiments are described in Part II1of this series. Hydrodynamic design aspects of a multistage fluidized bed are discussed in more detail in Part I

ISSN:0006-3592    

DOI:10.1002/bit.260360407

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn Part I of this series,1we derived a model and made simulations for a multistage fluidized bed reactor (MFBR). It was concluded that the MFBR can be an attractive alternative for a fixed bed reactor when operated with a deactivating biocatalyst. In Part II of this series, the design of a laboratory‐scale MFBR and its evaluation to investigate the practical feasibility of this reactor type, will be described. Experiments with a duration as long as 10 days were carried out successfully using immobilized glucose isomerase as a model reaction system. The results predicted by the model are in good agreement with the measured glucose concentration and biocatalyst activity gradients, indicating perfect mixing of the particles in the reactor compartments.The diameters of the biocatalyst particles used in the experiments showed a large spread, with the largest being 1.7 times the smallest. Therefore, an additional check was carried out, to make sure that the particles were not segregating according to size. Particles withdrawn from the reactor compartments were investigated using an image analyzer. Histograms of particle size distribution do not indicate segregation and it is concluded that the particles used have been mixed completely within the compartments. As a result, transport of biocatalyst is nearly plug flo

ISSN:0006-3592    

DOI:10.1002/bit.260360408

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn Parts I and II of this series we described the modelling, design, and operation of a multistage fluidized bed reactor (MFBR) for immobilized biocatalysts. This article deals with those aspects of the MFBR which are different from single‐stage fluidized beds which are operated in batch mode with respect to the solids. The semicontinuous transport of the particles requires perfect mixing of the particles in the reactor compartments, because particles are mainly transported from the bottom of these compartments. A large spread in the physical properties of the biocatalyst particles, especially of both size and density, may cause the particles to segregate into layers with different diameter and/or density. This affects the efficient use of the biocatalyst. The properties of the particles are dependent on the immobilization method. The suitability of different methods for possible future application in the MFBR is therefore compared. Because of segregation, successful use of a biofilm catalyst with a nonuniform thickness of the biofilm is doubtful. Experiments in a small scale reactor (± 0.1 m diameter) demonstrated that perfect particle mixing is possible using commercially available biocatalyst particles of uniform density. Co‐immobilization of the biocatalyst with glass powder in a gel is a simple and effective method of increasing gel density. High density particles allow high liquid flow rates, and thus an improved external mass transfer can be achieved.The distributor plates, which separate the reactor compartments, must allow unhindered transport of particles. Therefore, the holes in these plates must have a diameter of at least 4.5 times that of the largest particles which are present in the particle mixture used. Furthermore, the plates must be designed such that, when scaling‐up the reactor, a uniform liquid distribution over the cross‐sectional area of the reactor occurs. Large‐scale experiments were not carried out, but published correlations, indicate that particle mixing and a uniform liquid distribution can be accomplished in a large‐scale reactor under similar flo

ISSN:0006-3592    

DOI:10.1002/bit.260360409

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe use of a scroll decanter centrifuge for the removal and dewatering of affinity‐flocculated yeast cell debris from a crude homogenate is described. Laboratory shear modulus measurements were used to compare the structure of flocculated and nonflocculated sediments and to indicate the dewatering conditions under which the sediment could be discharged from the centrifuge. The structure of the flocculated sediment was such that a dry beach could be used within the centrifuge while still being able to discharge the solids. The scroll decanter performance for recovery and dewatering of the flocculated homogenate was found to be independent of feed flow rate and differential scroll rate. Eighty‐five percent of the solid material was recovered from the flocculated homogenate while the extent of sediment dewatering resulted in the loss of only 7% of the soluble protein in the sediment. The supernatant clarity matched that achieved by low‐gravity laboratory centrifugation st

ISSN:0006-3592    

DOI:10.1002/bit.260360410

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe gram‐positive bacteria,Acinetobacter calcoaceticus, is capable of accumulating biopolymer in the carrier matrix of an immobilized cell system. Several possible mechanisms for the biopolymer accumulation are evaluated. It appears that direct solid surface polymer adsorption and polymer diffusion limitation within the pore space are minor factors in biopolymer accumulation. Calculations demonstrate that the cell bound polymer to dry cell weight ratio is much higher for immobilized cells than for free cells. The higher cell‐bound polymer to dry‐cell‐weight ratio for immobilized cells as well as the accumulation of the immobilized cells in the Celite matrix are believed to be the main factors for biopolymer accumulation in the Carrier matrix. Further studies reveal that the cell‐bound polymer to dry‐cell‐weight ratio is strongly affected by shear forces. At zero shear stress, such as would be present in the carrier matrix, cell bound polymer to dry cell weight ratio can be as high as 1.6. As the shear stress increases, this ratio decreases. When shear stress increases above 5 dyn/cm2, a level equivalent to the shear experienced by free cells in a stirred tank fermentation, cell‐bound polymer decreases to less than 20% of dry cell weight. A macroscopic model is developed to describe the effect of shear stress on the cell‐bound polymer to dry

ISSN:0006-3592    

DOI:10.1002/bit.260360411

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

年代:1990

数据来源: WILEY