Showing papers in "Bioprocess Engineering in 1994"
TL;DR: In this paper, five sources of nitrogen, six minerals, six enzyme inducers and one each of growth as well as product promotors were screened by Plackett-Burman design, consisting of a total of 20 experiments for the above 19 sources/categories of medium ingredients, for their effect on the production of Aspergillus niger MRSS 234 in solid state fermentation system.
Abstract: Five sources of nitrogen, six minerals, six enzyme inducers and one each of growth as well as product promotors were screened by Plackett-Burman design, consisting of a total of 20 experiments for the above 19 sources/categories of medium ingredients, for their effect on the production of alpha-galactosidase by Aspergillus niger MRSS 234 in solid state fermentation system. The enzyme production was recorded from 2 to 5 days of fermentation. Data on enzyme titres was analysed by compatible analysis to obtain regression coefficients and t-ratios. Among the nitrogen sources, urea contributed positively to enzyme production and its effect increased with the fermentation time, in contrast to negative effect of all the ammonium salts used. Corn steep liquor, citric acid and legume seed flours showed significantly positive effects on enzyme production, though lactose showed negative effect upto 3 days of fermentation and then turned positive but not significantly. Calcium chloride and ferrous sulphate showed considerable negative effect, in contrast to mixed effect by other mineral salts studied. Among the legume seed flours, guar and French bean flours showed larger positive effects. The studies allowed the selection of urea, corn steep liquor, guar flour, soy bean flour and citric acid as most promising sources/categories for further optimization studies based on the effects as well as their trend with fermentation time. The use of Plackett-Burman design for rapid screening of large number of nutrients, in a very small number of experiments, for reliable short-listing of a few of most effective sources/categories for further optimization, has been scarce in submerged fermentation and never attempted earlier in solid state fermentation system.
101 citations
TL;DR: The strain employed showed no great dependence upon temperature and achieved its best yield of xylitol from d-xylose at a pH value of 2.5, which allows non sterile cultivation, which is a major economic factor.
Abstract: Candida tropicalis DSM 7524 was used to produce xylitol from d-xylose. The fermentation conditions were optimized during continuous cultivation. The strain employed showed no great dependence upon temperature in a range between 30° C and 37° C. It achieved its best yield of xylitol from d-xylose at a pH value of 2.5. Such low pH values allow non sterile cultivation, which is a major economic factor. With an oxygen uptake rate of 0.8–1 ml oxygen per litre culture medium, the C. tropicalis produce xylitol at a yield of between 77% and 80% of the theoretical value. Higher yeast extract concentrations prevent the conversion of d-xylose into xylitol. d-xylose acts as a growth inhibitor in higher concentrations. The maximum xylitol yield was reached at a d-xylose concentration of around 100 g/l. In a non sterile batch culture with substrate shift 220 g/l xylitol were produced from 300 g/l d-xylose at a xylitol productivity rate of 0.37 g/(lh). In order to increase the specific yield, C. tropicalis was immobilised on porous glass and cultivated in a fluidized bed reactor. In a continuous non sterile cultivation with immobilised cells 155 g/l d-xylose produced 90–95% g/l xylitol with a productivity of 1.35 g/(lh).
99 citations
TL;DR: A strain isolated locally and identified as Rhizopus oryzae (RO, IIT KGP) was found to synthesise an extracellular enzyme, tanin acyl hydrolase, showing its degradability of tannic acid to gallic acid.
Abstract: A strain isolated locally and identified as Rhizopus oryzae (RO, IIT KGP) was found to synthesise an extracellular enzyme, tanin acyl hydrolase, showing its degradability of tannic acid to gallic acid. For maximizing the enzyme secretion in the fermented broth, the influencing parameters were optimized in shake flask culture. Experiments showed that modified Czapek dox medium with 2% tannic acid, 1% glucose, 0.05% sodium nitrate incubated for 4 days with 2 days old inoculum was the optimum for the synthesis of tannase by Rhizopus oryzae (RO, IIT KGP). Maximum enzyme activity was found to be 6.12 U/ml.
95 citations
TL;DR: Variation in cell capacitance showed the possibility of using this method as a means to indicate changes in the physiological state of cells during cultivation, which would be very useful in designing control strategies that would depend on the physiological states in the bioprocess.
Abstract: Measurement of capacitance, also referred to as dielectric permittivity, is a new method of estimating the concentration of cells, monitoring the growth and detecting the physiological changes during the cultivation of organisms in various bioprocess. Several types of biological cells were studied, namely; Saccharomyces cerevisiae, Escherichia coli, Perilla frutescens (plant cells) and AFP-27 hybridoma cells. Generally, a linear correlation between cell capacitance (C) and other biomass measurement technique such as optical density (OD) and dry weight (DW) was obtained using the different types of cell suspension. Therefore, this method could be used to monitor the growth of the organism during the active growth. It could be conveniently used to make a rapid estimate of the cell concentration such as in plant cell suspension culture. The capacitance sensor could also be designed to be installed and autoclaved in-situ in a bioreactor and used for on-line monitoring of cell growth. On the other hand, distinct deviations in the capacitance value were observed in relation with the growth stage of the organism. This was observed in all the organisms studied but the type of deviation depends on the physiology of the organism. This variation in cell capacitance showed the possibility of using this method as a means to indicate changes in the physiological state of cells during cultivation. This capability would be very useful in designing control strategies that would depend on the physiological states in the bioprocess.
60 citations
TL;DR: A scale-up strategy for a nitrification process with immobilized cells is presented and a new element in this regime analysis is a solid third phase in which cells grow non-homogeneously.
Abstract: A scale-up strategy for a nitrification process with immobilized cells is presented. The complete description of such a process for a wide range of conditions is time consuming or even impossible. For a successful scale up of the process knowledge of the rate-limiting step is essential. To estimate the rate-limiting step a regime analysis was used. A new element in this regime analysis is a solid third phase in which cells grow non-homogeneously. Three different conditions of the nitrification process were considered: low temperature (7°C) with a low ammonia concentration (2 mM), and optimal temperature (30°C) with an ammonia concentration of 2 and 250 mM. The regime analysis proved to be a helpful tool for the understanding of the process and for establishing the rate-limiting step. A set of design rules for the different nitrification conditions was obtained from the results of this regime analysis.
57 citations
TL;DR: A kinetic model of solid state fermentation with temperature deactivation of microorganisms is presented in this paper, where the experimental results of cultivation of Aspergillus niger on a mixture of wheat bran and beet pulp in temperature range from 26 °C to 40 °C were used to estimate the parameters of the model.
Abstract: A kinetic model of solid state fermentation with temperature deactivation of microorganisms is presented. The experimental results of cultivation of Aspergillus niger on a mixture of wheat bran and beet pulp in temperature range from 26 °C to 40 °C were used to estimate the parameters of the model. The activation energies of growth, thermal deactivation and maintenance have been calculated.
55 citations
TL;DR: Pilot-scale experimental observations from three optical density probes, the Cerex, Monitek and Wedgewood designs, have been included for Escherichia coli fermentations.
Abstract: Commercially available on-line and in-situ devices for monitoring cell density are reviewed in this article Principles of operation are described as well as capabilities of these probes in specific measurement applications based on literature reports Pilot-scale experimental observations from three optical density probes, the Cerex, Monitek and Wedgewood designs, have been included for Escherichia coli fermentations Requirements for future on-line and in-situ instruments are discussed as well as the impact of current limitations on widespread application
52 citations
TL;DR: Pellets of Penicillium chrysogenum, which were spontaneously formed after a certain stage of a batch fermentation, displayed a considerable structural change in course of their lifetime as discussed by the authors.
Abstract: Pellets of Penicillium chrysogenum which were spontaneously formed after a certain stage of a batch fermentation, displayed a considerable structural change in course of their lifetime. Microelectrode studies showed the internal mass transport properties of these pellets (diameter 1–3 mm) to be highly effected by their morphological structure. Relatively young pellets, in an early stage of the batch fermentation, possessed a homogeneous and dense structure. These pellets were only partly penetrated by oxygen (ca. 70 μm) at air saturated bulk conditions. Older pellets, in a final stage of the batch fermentation, were stratified and fluffy. They were completely penetrated by oxygen due to a decreased activity and a higher diffusivity. Investigations with glucose microelectrodes revealed that glucose consumption inside pellets of all lifetimes exclusively occurred in the periphery, indicating that growth was restricted to these regions only.
45 citations
TL;DR: The enzymatic hydrolysis of olive oil using Chromobacterium viscosum lipase B encapsulated in reversed micelles of AOT in isooctane was carried out in a continous reversed mousellar membrane bioreactor confirming the high stability of this catalytic system.
Abstract: The enzymatic hydrolysis of olive oil using Chromobacterium viscosum lipase B encapsulated in reversed micelles of AOT in isooctane was carried out in a continous reversed micellar membrane bioreactor. A tubular ceramic membrane installed in an ultrafiltration module was used to retain the lipase and separate the products from the reaction media. Water filled micelles were supplemented to the reactor together with the substrate/solvent solution to compensate for the permeation of reversed micelles. The influence of substrate concentration, residence time and water content in the productivity and conversion of the system were investigated. A linear relationship between productivity and conversion degree was found for each substrate concentration tested. Operational stability of the bioreactor was tested in a long term operation confirming the high stability of this catalytic system.
33 citations
TL;DR: In this paper, a two phase anaerobic system was used to treat Olive mill wastewaters, diluted with tap water, and the effect of substrate concentration and phase separation on removal efficiency was investigated.
Abstract: The high organic content of Olive Mill Wastewaters (OMW) causes some difficulties in maintaining the anaerobic process efficiency at high level. The two phase anaerobic system was used to treat olive mill wastewaters, diluted with tap water. Phase separation was accomplished through control of the hydraulic retention time and initial COD removal in two reactors operated in series. The effect of substrate concentration and phase separation on removal efficiency has been investigated. Experimental results indicated that yield of 0.322 to 0.335 litre biogas/g COD removal were obtained with two phase anaerobic treatment and space loading rate of 2.3 and 2.4 gCOD/l.day. The maximum methane production rate near to the theoretical value and corresponded to 360 ml of CH4 for 1g COD removal.
32 citations
TL;DR: The criterion of constant OTR or constant kLa is not applicable for the scale-up of this oxygen-sensitive culture due to strong influence of reactor hydrodynamics under microaerobic conditions and the tower reactors have a 12 time higher energetic efficiency and thus should be the choice for large scale production of 2,3-butanediol.
Abstract: Stirred tank (STR), bubble column (BCR) and airlift (ALR) bioreactors of 0.05 and 1.5 m3 total volume were compared for the production of 2,3-butanediol using Enterobacter aerogenes under microaerobic conditions. Batch fermentations were carried out at constant oxygen transfer rate (OTR=35 mmol/lh). At 0.05 m3 scale, the STR reactor achieved much higher biomass and product concentrations than the BCR and ALR reactors. At 1.5 m3 scale, however, exactly the same biomass and product concentrations could be obtained in both STR and ALR reactors. The 1.5 m3 ALR reactor performed also much better than its counterpart at small scale, achieving a productivity 2.4-fold as high as that of the 0.05 m3 BCL and ALR reactors. No differences in performances were observed between BCR and ALR. As compared to STR the tower reactors have a 12 time higher energetic efficiency (referred to product formation) and thus should be the choice for large scale production of 2,3-butanediol. The criterion of constant OTR or constant k
L
a is not applicable for the scale-up of this oxygen-sensitive culture due to strong influence of reactor hydrodynamics under microaerobic conditions. The effects of mixing and circulation time on growth and metabolism of E. aerogenes were quantitatively studied in scaled-down experiments with continuous culture. For a successful scale-up of this microaerobic culture it is necessary to have an homogeneous oxygen supply over the entire reactor volume. Under conditions of inhomogeneous oxygen supply an optimum liquid circulation time exists which gives a maximum production of 2,3-butanediol.
TL;DR: In this article, the authors compare batch and fed-batch fermentation based on productivity and including the analysis of the implications on product manufacturing cost, and find that batch fermentation is more efficient than fedbatch fermentation.
Abstract: This article concerns the comparison between batch and fed-batch fermentation based on productivity and including the analysis of the implications on product manufacturing cost.
TL;DR: An attempt has been made to study the applicability of various model equations for substrate inhibited systems by fitting their experimental data and evaluating various parameters including the standard deviations in each case.
Abstract: The biochemical route is identified to be one of the simplest and cheapest means by which valuable chemicals are being synthesized. Microorganisms play a vital role in carrying out these processes. However, the kinetic studies relevant to this process is scarce. Most often inhibition effects due to either cells or substrates or products affect the performance of such processes. This paper deals with the study of various model equations for substrate inhibition kinetics. An attempt has been made to study the applicability of various model equations for substrate inhibited systems by fitting their experimental data and evaluating various parameters including the standard deviations in each case. Finally, a new model has been brought out which gives the best fit for almost all the systems.
TL;DR: In this article, the authors used the carbon and oxygen balance derived from exhaust data of Schizophyllum commune to predict the optimum operation condition for maximum glucan formation.
Abstract: Oxygen and shear stress are the key factors for enhanced glucan production with Schizophyllum commune. During batch cultivation control of \(P_{O_2 } \) or \(q_{O_2 } \) (specific oxygen uptake rate) was achieved by variation of the impeller speed. Biomass was modelled by using the carbon and oxygen balance derived from exhaust data. At mycel growth a \(q_{O_2 } \) of 0.042 h−1 presents just the border before oxygen limitation arises and is simultaneously the optimum operation condition for maximum glucan formation. Related to an overall cultivation time of 72 h a maximum of both productivity (4.3 kg m−3 d−1) and yield (13 kg m−3) were obtained.
TL;DR: In this article, a two-stage plant with specially adapted and immobilized microorganisms fixed on broken sand particles was used for the production of naphthol the coupling compound in the syntheses of azo-dyes.
Abstract: The production of naphthol the coupling compound in the syntheses of azo-dyes occurs a naphthalenesulphonic acid-containing wastewater. The aerobic biodegradation of a complex mixture of naphthalenemono- and -disulphonic acids with high amounts of inorganic salts was examined in a two-stage plant with specially adapted and immobilized microorganisms fixed on broken sand particles. The plant consists of two airlift-loop reactors. An interposed settling tank separates the two different bacterial communities in the stages. In the first stage the sequential metabolization of naphthalene-2- and-1-sulphonic acid was achieved by strain Pseudomonas testosteroni A3 at residence times down to 1.5 h. The total degradation of remaining naphthalene-1-sulphonic acid and the degradation of recalcitrant naphthalenedisulphonic acids was obtained by a defined mixed culture in the second unit. Because of the more recalcitrant character of the remaining components in the second stage examinations with Na2SO4-loaded and salt-free wastewater were carried out at mean residence times between 50 and 6.3 h. With salt-loaded sewage an overall degradation of approximately 71% was achieved. The main component in the effluent was non-biodegradable naphthalene-1.5-disulphonic acid. Investigations with salt-free wastewater have shown an increasing overall degradation up to 84%. Thus, in the presence of inorganic salts a considerable inhibition of the biological degradation of the recalcitrant substances in the second unit was found.
TL;DR: It was found that the dependency of cellular enzyme activity on the shear stress and the exposure time was related to the transmission of the energy from the flowing medium to attached cells.
Abstract: The effect of shear stress on the activity of cellular enzyme in an animal cell was discussed by using a flow channel. The activity of lactate dehydrogenase (LDH) in cells exposed to a shear stress of 0.5 Pa for 12 h was about 4-fold greater than in the cells without exposure to shear stress. The relative LDH activity was correlated with the dissipation energy density of the flowing medium. A good correlation was obtained and it was found that the dependency of cellular enzyme activity on the shear stress and the exposure time was related to the transmission of the energy from the flowing medium to attached cells.
TL;DR: Protein and cutinase activity global yields of 38 and 45%, respectively, were obtained for the global process, extraction and back-extraction steps, using low ionic strength, pH 9.0, 100 mM AOT and 20°C.
Abstract: This work deals with the extraction and back-extraction of a recombinant cutinase using AOT reversed micelles in isooctane. The effect of pH, ionic strength, AOT concentration and temperature on the extraction and back-extraction of the cutinase was investigated. High extraction (97%) of the cutinase was achieved at pH 7.0 with a 50 mM Tris-HCl buffer solution containing 100 mM KCl, but a low activity was detected in the reversed micellar phase. At pH 9.0, cutinase was extracted (75%) to the reversed micelles with higher activity. Cutinase was recovered (50%) from a reversed micellar phase (100 mM AOT/isooctane) into a 50 mM Tris-HCl buffered solution at pH 9.0 with 100 mM KCl, and 20°C. Protein and cutinase activity global yields of 38 and 45%, respectively, were obtained for the global process, extraction and back-extraction steps, using low ionic strength, pH 9.0, 100 mM AOT and 20°C.
TL;DR: In this paper, a polynomial model of a suitable degree for tannin acyl hydrolase production by Aspergillus niger PKL 104 in a solid state fermentation system was used for optimization of five parameters (initial moisture, initial pH, incubation temperature, inoculum ratio and fermentation period).
Abstract: Optimization of five parameters (initial moisture, initial pH, incubation temperature, inoculum ratio and fermentation period), as per central composite rotable design falling under the response surface methodology, was attempted in a total of 32 experimental sets, after fitting the experimental data to the polynomial model of a suitable degree, for tannin acyl hydrolase production by Aspergillus niger PKL 104 in solid state fermentation system. The quantitative relation between the enzyme production and different levels of these factors was exploited to work out optimized levels of these parameters by flexible polyhedron search method and confirmed by further experimentations. The best set required 5% inoculum, 6.5 initial pH, 28 °C fermentation temperature, 62% initial moisture and 3 days fermentation time. The optima were worked out under the additional constraints for temperature (∼ 30 °C) and fermentation time (not more than 3 days) which are essential from industrial conditions and to pre-empt contamination, respectively. The best set resulted in 1.34 times more enzyme production than that was obtained before this optimization. Three dimensional plots, relating the enzyme production to paired factors (when other three factors were kept at their optimal levels) best described the behaviour of solid state fermentation system and the interactions between factors under optimized conditions. The model showed that the enzyme production was affected by all the five factors studied. The initial pH exhibited a positive interaction with moisture but no interaction with other factors. Initial moisture level and inoculum ratio showed negative interaction in contrast to positive interaction between inoculum ratio and fermentation period. It is thus apparent that the response surface methodology not only gives valuable information on interactions between the factors but also leads to identification of feasible optimum values of the studied factors, in addition to 99% (or more) savings on resources as compared to a full factorial traditional optimization method. Response surface methods have not been used earlier for optimizing parameters in solid state fermentation system.
TL;DR: The parameters involved in immobilization of alkaline protease on nylon using glutaraldehyde as coupling agent and the characteristics of the immobilized enzyme were investigated and immobilized enzyme showed better thermal stability than the free enzyme.
Abstract: The parameters involved in immobilization of alkaline protease on nylon using glutaraldehyde as coupling agent and the characteristics of the immobilized enzyme were investigated. Optimum temperature and pH of both free and immobilized enzyme for the degradation of protein was found. Immobilized enzyme showed better thermal stability than the free enzyme. The reusability and storage stability of the immobilized enzyme was also studied.
TL;DR: In this article, two types of bioreactor using a flocculating strain of Saccharomyces cerevisiae and continuous ethanolic fermentation as model were compared in terms of start-up evolution, overall performance and power costs.
Abstract: Two types of bioreactor using a flocculating strain of Saccharomyces cerevisiae and continuous ethanolic fermentation as model were compared in terms of start-up evolution, overall performance and power costs. Also, the effect of adding to the medium a polymer — Magna Floc LT25 — that increases floc porosity was studied.
TL;DR: In this paper, a cylindrical pilot plant fermenter was used to study mixing characteristics and the mechanisms of homogenization during beer fermentation, and the degree of mixture or homogeneity, correlated throughout the fermentation process, with the mixing power, defined in terms of CO2 production rate.
Abstract: Beer fermentations carried out in a cylindrical pilot plant fermenter were used to study mixing characteristics and the mechanisms of homogenization during beer fermentation. The evolution of different parameters (pH, dry weight, sugars and ethanol concentration) were monitored at different heights within the fermenter, which was inoculated in its upper part. The degree of mixture or homogeneity, was correlated throughout the fermentation process, with the mixing power, defined in terms of CO2 production rate. In the final model obtained, the influence of solids evolution on the mixing bulk was also taken into account.
TL;DR: In this paper, hardwood hemicellulose acid hydrolysates, enriched in pentoses through countercurrent operations, have been fermented by Pachysolen tannophilus NRRL Y2460 in batch reactors.
Abstract: Hardwood hemicellulose acid hydrolysates, enriched in pentoses through countercurrent operations, have been fermented by Pachysolen tannophilus NRRL Y2460 in batch reactors. In order to evaluate the effects of pentose as well as inhibitor concentrations on the overall ethanol yield, several materials have been used for the physical treatment of this hydrolysate: Fly ash, a mixture of ionexchange resins, a porous material constituted by SiO2 and Al2O3 and a mixture of organic solvents. The best combination, consisting of an overliming pretreatment followed by a secondary treatment in a column filled with the Si-Al material, has assured an increase in ethanol concentration of 15%. Finally, the data of continuous fermentations of these hydrolysates in an immobilized-cell reactor are presented and discussed.
TL;DR: A fed-batch feeding strategy is proposed to allow for an accurate estimation of yield and of critical growth rate of baker's yeast and is therefore suitable for routine use in screening of strains and media.
Abstract: Parameter identification of structured models is often a problem in biotechnology, because the poor data situation and the number of unknown parameters only allow for inaccurate estimates. But often only a subset of all kinetic parameters of the model are of interest for production purposes, e.g. for fed-batch cultivation. These parameters should be estimated with a given accuracy. In addition, the experiments for information acquisition with respect to these parameters should be as simple as possible and should consider some practical restrictions. In this contribution a fed-batch feeding strategy is proposed to allow for an accurate estimation of yield and of critical growth rate of baker's yeast. The feeding also allows for economic and stereotyped use of staff and equipment and is therefore suitable for routine use in screening of strains and media. The overall pattern is similar to that one, usually used in production scale to minimize errors by limited model validity. After an initial phase for achieving a reproducible state three different growth rates are adjusted to cover the range of possible critical growth rates. From biomass and ethanol measurements yield and critical growth rate can be estimated with an accuracy of about 2.1%. The fermentation pattern ends up with a constant feeding rate to simulate a limited oxygen transfer rate and to allow for an uptake of residual sugar and ethanol before a dough test can be carried out. Beside experimental results simulations and sensitivity analyses are shown.
TL;DR: In this paper, a nonlinear PI controller was proposed for a bioreactors exhibiting two input multiplicities, i.e., steady state gains having opposite signs, and the performance of the nonlinear controller was compared with that of the linear PI controller designed for the overall linear system.
Abstract: Control of bioreactors exhibiting two input multiplicities, ie, steady-state gains having opposite sign, is theoretically analyzed The nonlinear system is represented by a unity gain linear system cascaded with a nonlinear gain A conventional PI controller designed for the linear portion of the system followed by the solution of the nonlinear gain equation gives a nonlinear controller The performance of the nonlinear controller is compared with that of the linear PI controller designed for the overall linear system The nonlinear PI controller performance is superior to that of the linear PI controller
TL;DR: Improvements of the glucose fermentation by immobilized Saccharomyces cerevisiae in a packed-bed bioreactor are attributable to a mechanical effect rather than to physiological changes of microorganisms.
Abstract: When the immobilized cells are employed in packed-bed bioreactors several problems appear. To overcome these drawbacks, a new bioreactor based on the use of pulsed systems was developed [1]. In this work, we study the glucose fermentation by immobilized Saccharomyces cerevisiae in a packed-bed bioreactor. A comparative study was then carried out for continuous fermentation in two packed-bed bioreactors, one of them with pulsed flow. The determination of the axial dispersion coefficients indicates that by introducing the pulsation, the hydraulic behaviour is closer to the plug flow model. In both cases, the residence time tested varied from 0.8 to 2.6 h. A higher ethanol concentration and productivity (increases up to 16%) were achieved with the pulsated reactors. The volumes occupied by the CO2 were 5.22% and 9.45% for fermentation with/without pulsation respectively. An activity test of the particles from the different sections revealed that the concentration and viability of bioparticles from the two bioreactors are similar. From the results we conclude that the improvements of the process are attributable to a mechanical effect rather than to physiological changes of microorganisms.
TL;DR: The results presented show that neural networks can model very accurately the dynamics of a continuous stirred tank fermenter and, the neural model, when used recursively, can predict the state variables over a long prediction horizon with sufficient accuracy.
Abstract: Feedforward neural networks are a general class of nonlinear models that can be used advantageously to model dynamic processes. In this investigation, a neural network was used to model the dynamic behaviour of a continuous stirred tank fermenter in view of using this model for predictive control. In this system, the control setpoint is not known explicitly but it is calculated in such a way to optimize an objective criterion. The results presented show that neural networks can model very accurately the dynamics of a continuous stirred tank fermenter and, the neural model, when used recursively, can predict the state variables over a long prediction horizon with sufficient accuracy. In addition, neural networks can adapt rapidly to changes in fermentation dynamics.
TL;DR: It is suggested that cell density dictates the rate of glucose consumption while the cell growth rate influences how glucose is metabolized, i.e., through glycolysis or the TCA cycle.
Abstract: In this work, metabolite and antibody production kinetics of hybridoma cultures were investigated as a function of cell density and growth rate in a homogeneous perfusion reactor. Hydrophilized hollow fiber polypropylene membranes with a pore size of 0.2 μm were used for medium perfusion. Oxygen was supplied to the cells through thin walled silicone tubing. The mouse-mouse hybridoma cells were grown in three identical bioreactors at perfusion rates of 1.1, 2.0, and 3.2/day for a period of eight days during which the viable cell concentrations reached stable values of 2.6×106, 3.5×106, and 5.2×106 cells/ml, respectively. Total cell densities reached values ranging from 8×106 to 1×106 cells/ml. Specific substrate consumption and product formation rates responded differently to changes in cell density and apparent specific growth rate, which were not varied independently. Using multiple regression analysis, the specific glucose consumption rate was found to vary with viable cell density while the specific glutamine uptake and lactate production rates varied with both viable cell density and apparent specific growth rate. These results suggest that cell density dictates the rate of glucose consumption while the cell growth rate influences how glucose is metabolized, i.e., through glycolysis or the TCA cycle. The specific antibody production rate was found to be a strong function of cell density, increasing as cell density increased, but was essentially independent of the specific growth rate for the cell line under study.
TL;DR: In this paper, a new pulsing device which permits the insertion in pulsing form of a liquid phase fed into an equipment where a microbial or enzymatic transformation occurs is described, and modifications of the flow model caused by the pulsation generated by means of three kinds of pulsators: a hydropneumatic pulsator, a selfpropelled pulsator and a newly designed elastic membrane pulsator.
Abstract: This paper describes a new pulsing device which permits the insertion in pulsing form of a liquid phase fed into an equipment where a microbial or enzymatic transformation occurs. It also analyzes the modifications of the flow model caused by the pulsation generated by means of three kinds of pulsators: A hydropneumatic pulsator, a selfpropelled pulsator and a newly designed elastic membrane pulsator.
TL;DR: The yield of gluconic acid was influenced more by a combination of metal ions rather than individual ions, and potassium ferrocyanide treatment gave the most promising results compared to other treatment techniques.
Abstract: Gluconic acid fermentation by Aspergillus niger has been investigated using untreated and treated Indian cane molasses. The yield of gluconic acid was found to be reduced using an untreated molasses medium compared to a defined medium. Hence, molasses was subjected to various pretreatment techniques. Pretreatment reduced the levels of various cations and anions. As the synthesis of gluconic acid has been observed to be influenced more by cations than anions, the effect of various metal ions, viz., copper, iron, zinc, manganese, calcium, and magnesium on the yield of gluconic acid has been critically examined in both untreated and treated cane molasses. These results have been compared with a defined medium. The yield of gluconic acid was influenced more by a combination of metal ions rather than individual ions. Potassium ferrocyanide treatment gave the most promising results compared to other treatment techniques.
TL;DR: In this article, the continuous aerobic transformation of synthetic cyanide waste-water, amygdalin solutions and almond seed extract containing cyanide was investigated in several fluidized bed reactors, and various inocula consisting of activated sludge or soil slurry were used.
Abstract: The continuous aerobic transformation of synthetic cyanide waste-water, amygdalin solutions and almond seed extract containing cyanide was investigated in several fluidized bed reactors. Various inocula consisting of activated sludge or soil slurry were used. Successful inoculation was achieved with simple soil slurry. No significant influence was found between the performance of the systems inoculated with a cyanide contaminated soil and a garden soil. The performance and stability of the reactors with respect to degradation rate were tested for a range of cyanide loading conditions, with feed containing only cyanide, and with different additional carbon sources, as well as various C∶N ratios at a hydraulic retention time of 24 h. No growth with cyanide as the sole source of carbon and nitrogen was observed. The system with lactate as the organic C-source was capable of operating at cyanide concentrations of 160 ppm cyanide with a conversion rate of 0.125 kg cyanide/m3 d. Ammonia was the end product and the effluent concentration was 0.5 ppm CN−. The systems with ethanol as the organic C-source could degrade only 0.05 kg cyanide/m3 d, whose feed concentration was 60 ppm cyanide. Amygdalin, an organic cyanide-containing compound present in stone fruit seeds, was fed as a model substrate. Degradation rates up to 1.2 kg COD/m3 d could be measured with no free or organically bound cyanide in the effluent. These rates were limited by oxygen transfer, owing to the large amount of degradable COD. The further investigations with almond seed extracts, confirmed the applicability of the aerobic process to treat food-processing waste streams having low concentrations of cyanide with high COD content.