Showing papers in "Biotechnology and Bioengineering in 1987"
TL;DR: General rules for the optimization of different biocatalytic systems in various types of media containing organic solvents are derived by combining data from the literature, and the logarithm of the partition coefficient, log P, as a quantitative measure of solvent polarity.
Abstract: General rules for the optimization of different biocatalytic systems in various types of media containing organic solvents are derived by combining data from the literature, and the logarithm of the partition coefficient, log P, as a quantitative measure of solvent polarity. (1) Biocatalysis in organic solvents is low in polar solvents having a log P 4. It was found that this correlation between polarity and activity parallels the ability of organic solvents to distort the essential water layer that stabilizes the biocatalysts. (2) Further optimization of biocatalysis in organic solvents is achieved when the polarity of the microenvironment of the biocatalyst (log P(i)) and the continuous organic phase (log P(cph)) is tuned to the polarities of both the substrate (log P(s)) and the product (log P(p)) according to the following rules: |log P(i) - log P(s)| and |log P(cph) - log P(p)| should be minimal and |log P(cph) - log P(s)| and |log P(i) - log P(p)| should be maximal, with the exception that in the case of substrate inhibition log P(i), should be optimized with respect to log P(s) In addition to these simple optimization rules, the future developments of biocatalysis in organic solvents are discussed.
1,540 citations
TL;DR: Peroxidase‐catalyzed copolymerization of different phenols in 85% dioxane was demonstrated, and poly(p‐phenylphenol) was found to have a much higher electrical conductivity than phenol‐formaldehyde resins.
Abstract: Polymers produced by horseradish-peroxidase-catalyzed coupling of phenols have been explored as potential substitutes for phenol-formaldehyde resins. To overcome low substrate solubilities and product molecular weights in water, enzymatic polymerizations in aqueous-organic mixtures have been examined. Peroxidase vigorously polymerizes a number of phenols in mixtures of water with water-miscible solvents such as dioxane, acetone, di-methylformamide, and methyl formate with the solvent content up to 95%. As a result, various phenolic polymers with average molecular weights from 400 to 2.6 x 10(4) D were obtained depending on the reaction medium composition and the nature of the phenol. Peroxidase-catalyzed copolymerization of different phenols in 85% dioxane was demonstrated. Poly(p-phenylphenol) and poly(p-cresol) were enzymatically prepared on a gram scale. They had much higher melting points, and in addition, poly(p-phenylphenol) was found to have a much higher electrical conductivity than phenol-formaldehyde resins.
374 citations
TL;DR: The inhibitory effect of butanol on yeast growth has been studied for the strain Candida utilis ATCC 8205 growing aerobically on butanol under batch conditions and a mathematical expression was proposed to fit the kinetic pattern ofbutanol inhibition on the specific growth rate.
Abstract: The inhibitory effect of butanol on yeast growth has been studied for the strain Candida utilis ATCC 8205 growing aerobically on butanol under batch conditions. A mathematical expression was then proposed to fit the kinetic pattern of butanol inhibition on the specific growth rate: micro = micro mS/Ks + S [1 - S/Sm]n. The maximum allowable butanol concentration above which cells do not grow was predicted to be 9.16g/L. The proposed model appears to accurately represent the experimental data obtained in this study and the literature data developed for a variety of batch culture systems at widely ranging substrate concentrations.
287 citations
TL;DR: Biological denitrification of drinking water was studied in a fluidized sand bed reactor using a mixed culture using Hydrogen gas as the reaction partner and reaction kinetics were calculated with a double Monod saturation function.
Abstract: Biological denitrification of drinking water was studied in a fluidized sand bed reactor using a mixed culture. Hydrogen gas was used as the reaction partner. The reaction kinetics were calculated with a double Monod saturation function. The K(s) value for hydrogen was below 0.1% of saturation. No appreciable biofilm diffusion effects were detected. Reactor performance was a function of the culture's past history. Batch experiments always exhibited an accumulation of NO(2) (-), but continuous experiments with a sufficiently long residence time always resulted in complete nitrogen removal. Rates of up to 23 mg N/L h, 25 mg N/g DW h, and 7.9 mg H(2)/L h were achieved. Residence times of 4.5 h would be required for complete denitrification of water containing 25 mg NO(3) (-)-N/L or approximately 1 h for every 5 mg/L.
242 citations
TL;DR: The adhesion of three microorganisms (Saccharomyces cerevisiae, Acetobacter aceti, and Moniliella pollinis) to different materials has been studied using various supports (glass, metals, plastics), some of which were treated by an Fe(III) solution.
Abstract: The adhesion of three microorganisms (Saccharomyces cerevisiae, Acetobacter aceti, and Moniliella pollinis) to different materials has been studied using various supports (glass, metals, plastics), some of which were treated by an Fe(III) solution. The surface properties of the cells were characterized by the zeta potential and an index of hydrophobicity; characterization of the supports involved surface chemical analysis (XPS) and contact angle measurements. Cell suspensions in pure water at a given pH were left to settle on plates; the latter were then rinsed and examined microscopically, Saccharomyces cerevisiae and A. aceti adhere to metals under certain pH conditions but do not adhere to any of the other materials tested unless it is previously treated by ferric ions; adhesion of these hydrophilic cells is essentially controlled by electrostatic interactions. Moniliella pollinis adhere spontaneously to glass and to polymeric materials, but its attachment is also influenced by cell-cell or cell-support electrostatic repulsions; near the cell isoelectric point, cell flocculation is competing with adhesion to a support.
239 citations
TL;DR: Water washing of unexploded steamed aspenwood chips was at least as efficient as that of similarly treated but exploded chips and extensive rupturing of vessel pit membranes and other morphological features associated with steam‐exploded wood were shown.
Abstract: Pretreatment methods were compared with steam explosion, and differing views on the relative importance of mechanical and chemical effects were outlined. Hydrolysis was desirable; pyrolysis was undesirable. The effects of initial moisture content on steam consumption, mechanism and rate of heat transfer, pentosan solubilization, and subsequent glucose yield were summarized. The insignificant effect, after treatment at 240 degrees C, of 90% pressure bleed-down before explosion on subsequent simultaneous saccharification and fermentation (SSF) yields was described. Treatment at 190 degrees C with complete bleed-down (no explosion), when compared with that at 240 degrees C with explosion from full pressure, showed at least as good solubilization of pentosan, enzymatic hydrolysis, and SSF but showed greater pentosan destruction for the same degree of pentosan removal. Water washing of unexploded steamed aspenwood chips was at least as efficient as that of similarly treated but exploded chips. Scanning electron micrographs of unexploded chips showed extensive rupturing of vessel pit membranes and other morphological features associated with steam-exploded wood. Neither the explosion nor the high temperatures (above 190 degrees C) are necessary. 28 references.
198 citations
TL;DR: Control of the amount of water in the reaction system was found to be a valuable tool for the orientation of the reaction process and for the determination of the final reaction products.
Abstract: Immobilized lipase activity is studied in organic solvent systems of controlled water content under the influence of a variety of reaction parameters, such as temperature, relative humidity, substrate concentrations, and type of fatty acid used. Control of the amount of water in the reaction system was found to be a valuable tool for the orientation of the reaction process and for the determination of the final reaction products. The properties of the immobilized lipase were studied using the interesterification of triolein and palmitic acid as the model system.
193 citations
TL;DR: Investigation of enzymatic lactose hydrolysis by β‐galactosidase (lactase) was investigated with respect to the formation of oligosaccharides, findingMechanisms and possible ways of modelling enzymic lactose Hydrolysis, including formation of aggregates are presented.
Abstract: Enzymatic lactose hydrolysis by beta-galactosidase (lactase) was investigated with respect to the formation of oligosaccharides. An analysis of the formation of oligosaccharides and their control is important in the development of technical applications for enzymatic lactose hydrolysis. The available literature data on transfer reactions of lactase were reviewed, compared, and presented in a concise tabular form. Mechanisms and possible ways of modelling enzymatic lactose hydrolysis, including formation of oligosaccharides, are presented.
171 citations
TL;DR: Kinetic measurements indicated that only part of the adsorbed enzyme molecules are hydrolytically active, and no relation could be found between adsorption affinity and degree of randomness in cellulose hydrolysis, measured as the diversity of released hydrolytic products.
Abstract: Adsorption on crystalline cellulose of six endoglucanases (Endo I, II, III, IV, V and VI; 1, 4-beta-D-glucan glucanohydrolase, EC 3.2.1.4) and two exoglucanases (Exo II and III; 1,4-beta-D-glucan cellobiohydrolase, EC 3.2.1.92), purified from a commercial cellulase preparation of Trichoderma viride origin, was studied. Endo I, III, and V adsorbed strongly on Avicel cellulose, while adsorption of Endo II, IV, and VI was much lower. Also, the two exoglucanases could be divided into one enzyme (Exo III) that had a high adsorption affinity and another enzyme (Exo II) that adsorbed only moderately. Adsorption data fitted the Langmuir-type adsorption isotherm. However, adsorption was only partially reversible with respect to dilution. No relation could be found between adsorption affinity and degree of randomness in cellulose hydrolysis, measured as the diversity of released hydrolytic products. Kinetic measurements indicated that only part of the adsorbed enzyme molecules are hydrolytically active.
153 citations
TL;DR: The cost calculation of chemicals required for the immobilization of activated sludge by this PVA–boric acid method was proved to be extremely inexpensive for the ignition ofactivated sludge.
Abstract: A new method (polyvinyl alcohol–boric acid method) for an inexpensive and effective immobilization of activated sludge was developed. Using activated sludge immobilized by this PVA–boric acid method, synthetic waste-water was treated at a high loading rate of 0.5–2.35 kg TOC/m3 day. Total organic carbon and total nitrogen were removed at efficiencies of 93 and 30–40%, respectively. The kinetic constants Y and b for this immobilized activated-sludge process were determined to be 0.594g mixed liquor suspended solids (MLSS)/g TOC and 0.0219 day−1, respectively. The cost calculation of chemicals required for the immobilization of activated sludge by this PVA–boric acid method was proved to be extremely inexpensive for the immobilization of activated sludge.
152 citations
TL;DR: Thiobacillus denitrificans was observed to be very sensitive to CH3SH but relatively tolerant of CS2, COS, and CH3SCH3, and relative insensitivity to pressurization–depressurization cycles were demonstrated.
Abstract: It has been demonstrated that Thiobacillus denitrificans may be readily cultivated anaerobically in batch reactors on H(2)S (g) under sulfide-limiting conditions Under these conditions sulfide concentrations in the culture medium were less than 1 microM, resulting in very low concentrations of H(2)S in the reactor outlet gas The stoichiometry of the reaction was determined, and stable reactor operation was demonstrated at reactor loadings as high as 4-5 mmol H(2)S oxidized/h g biomass Maximum loading was estimated at 54-76 mmol H(2)S/h g biomass under the conditions employed in this study Indicators of reactor upset were determined and recovery from upset conditions demonstrated Barotolerance of T denitrificans to 125 MPa as well as a relative insensitivity to pressurization-depressurization cycles were also demonstrated T denitrificans was observed to be very sensitive to CH(3)SH but relatively tolerant of CS(2), COS, and CH(3)SCH(3)
TL;DR: The technique of autohydrolysis steam explosion was examined as a means for pretreatment of sugarcane bagasse to achieve high total sugar yield with moderate enzyme requirement and only minor losses due to sugar decomposition.
Abstract: The technique of autohydrolysis steam explosion was examined as a means for pretreatment of sugarcane bagasse. Treatment conditions were optimized so that following enzymatic hydrolysis, pretreated bagasse would give 65.1 g sugars/100 g starting bagasse. Released sugars comprised 38.9 g glucose, 0.6 g cellobiose, 22.1 g xylose, and 3.5 g arabinose, and were equivalent to 83% of the anhydroglucan and 84% of the anhydroxylan content of untreated bagasse. Optimum conditions were treatment for 30 s with saturated steam at 220/sup 0/C with a water-to-solids ratio of 2 and the addition of 1 g H/sub 2/SO/sub 4//100 g dry bagasse. Bagasse treated in this manner was not inhibitory to fermentation by Saccharomyces uvarum except at low inoculum levels when fermentation time was extended by up to 24 h. Pretreated saccharified bagasse was inhibitory to Pachysolen tannophilus and this was attributed to the formation of acetate from the hydrolysis of acetyl groups present in the hemicullulose. The major advantage of the pretreatment is the achievement of high total sugar yield with moderate enzyme requirement and only minor losses due to sugar decomposition.
TL;DR: Numerical simulations were developed that incorporate spatially heterogeneous catalytic and inactivation processes that are consistent with the reaction of hydrogen peroxide and certain catalytic intermediates of both enzymes.
Abstract: Homogeneous membranes containing immobilized glucose oxidase and catalase were stored in buffered solutions at 37 degrees C to determine the mechanisms and rates of catalyst inactivation. The experiments were designed so that inactivation occurred homogeneously throughout the membrane, thereby simplifying the analysis. The mechanism of inactivation is consistent with the reaction of hydrogen peroxide and certain catalytic intermediates of both enzymes. Based on this information, numerical simulations were developed that incorporate spatially heterogeneous catalytic and inactivation processes.
TL;DR: Previously defined fermentation conditions employing glucose as a carbon source were applied to this strain, resulting in high ceil densities with higher plasmid stability, and various methods of galactose induction of IFN‐γ expression in high‐cell‐density fermentations were investigated.
Abstract: Conditions for high-cell-density fermentations of Saccharomyces cerevisiae strains producing recombinant-DNA-derived proteins were established. Strains producing human immune interferon (IFN-gamma) from the constitutive PGK promoter failed to grow to high cell densities and exhibited low plasmid stability. Regulated expression of IFN-gamma was obtained in similar strains by employing a hybrid yeast GPD promoter that was subject to carbon source regulation due to the presence of regulatory DNA sequences from the yeast GAL 1,10 intergenic region. IFN-gamma expression programmed by this vector was low during growth on glucose and was induced by galactose. Previously defined fermentation conditions employing glucose as a carbon source were applied to this strain, resulting in high ceil densities with higher plasmid stability. Various methods of galactose induction of IFN-gamma expression in high-cell-density fermentations were investigated. Optimal conditions resulted in a 2000-fold induction and production of 2 g IFN-gamma/L fermentation culture.
TL;DR: A two‐parameter deactivation model is proposed to describe the kinetics of activity stabilization for some enzymes and the usefulness of the model is demonstrated by applying it to the inactivation of different enzymes.
Abstract: A two-parameter deactivation model is proposed to describe the kinetics of activity stabilization for some enzymes. The single-step unimolecular mechanism exhibits non-first-order deactivation kinetics since the final enzyme state, E(1) is not completely inactivated. The usefulness of the model is demonstrated by applying it to the inactivation of different enzymes. The influence of the concentration of active ester, ionic strength, and pH on the model parameters is examined during the inactivation of electric eel acetylcholinesterase.(25) In general, inactivators would decrease the level of activity stabilization, alpha(1), and increase the first-order inactivation rate constant, k(1). The effect of protecting agents would be to increase alpha(1) and to decrease k(1).
TL;DR: The ratio between the heat generated and the biomass formed, the so‐called “heat yield” (YQ/x), has been shown both on theoretical and experimental grounds to increase with increasing degree of reduction of the substrate and to decrease with increasing biomass yield.
Abstract: A modified bench scale calorimeter has been employed to det. the heat generated by various microbial strains growing on a range of different substrates, covering degrees of redn. from 3 to 6.13. The results are analyzed and interpreted in the light of coupled enthalpy and elemental balances. The heat released by the microbial cultures has been found to correlate linearly with other process variables, such as biomass generation and oxygen uptake. The ratio between the heat generated and the biomass formed, the so-called heat yield, has been shown both on theor. and exptl. grounds to increase with increasing degree of redn. of the substrate and to decrease with increasing biomass yield. The two effects could be combined into a simple model which permits the amt. of heat released per unit of biomass formed to be predicted from the degree of redn. of the substrate as the only independent variable. The ratio between the heat generated and the oxygen taken up was const. at 440 kJ (mol O2)-1 throughout all expts., as expected from theor. considerations for strongly aerobic processes. [on SciFinder (R)]
TL;DR: Enzymatic lactose hydrolysis using two yeast and two fungal lactases that are of current technical interest was studied and a possibility of enzymatics lactose recombination from its Hydrolysis products was shown.
Abstract: Enzymatic lactose hydrolysis using two yeast and two fungal lactases that are of current technical interest was studied. The enzymes were compared regarding their oligosaccharide production. Parameters influencing oligosaccharide formation, together with the effect of immobilization were examined and conditions minimizing oligosaccharide content in the hydrolysis product were proposed. Enzymatic whey hydrolysis was also considered. A possibility of enzymatic lactose recombination from its hydrolysis products was shown.
TL;DR: A kinetic model with substrate inhibition was developed and can be used to simulate the methane formation from M. mazei strain S6, which had the highest specific growth rate at all acetate concentrations studied and was least sensitive to environmental factors investigated.
Abstract: Kinetics of methanogenesis from acetate was studied using pure cultures of Methanosarcina barkeri and Methanosarcina mazei. Methane formation was found to be associated with cell growth. Nearly equimolar methane was produced from acetate during the methanogenic growth, and about 1.94 g of cells were formed from each mole of acetate consumed. Cell growth can be estimated from methane production. Significant substrate inhibition was found when acetate concentration was higher than 0.12 M. Among the three methanogenic strains studied, M. mazei strain S6 had the highest specific growth rate at all acetate concentrations studied and was least sensitive to environmental factors investigated (e.g., acetate concentration). The maximum specific growth rate found for strain S6 was 0.022 hr(-1) at acetic acid concentration around 7 g/L. The other two strains studied were M. barkeri strain 227 and strain MS. Growth of M. barkeri was completely inhibited at sodium acetate concentrations higher than 0.24 M. The maximum specific growth rate found for strains 227 and MS was 0.019 and 0.021 h(-1) at acetic acid concentrations of 3.6 and 6.8 g/L, respectively. A kinetic model with substrate inhibition was developed and can be used to simulate the methane formation from M. mazei strain S6 grown on acetate at 35 degrees C, pH 7.
TL;DR: In this article, the elasticity coefficients of enzymes in a linear and branched pathway were used to determine which properties of enzymes should be changed in order to obtain the maximal concentration of a metabolite or the maximal metabolic flux.
Abstract: The metabolic control theory developed by Kacser, Burns, Heinrich, and Rapoport is briefly outlined, extended, and transformed so as optimally to address some biotechnological questions. The extensions include (i) a new theorem that relates the control of metabolite concentrations by enzyme activities to flux ratios at branches in metabolic pathways; (ii) a new theorem that does the same for the control of the distribution of the flux over two branches; (iii) a method that expresses these controls into properties (the so-called elasticity coefficients) of the enzymes in the pathway; and (iv) a theorem that relates the effects of changes in metabolite concentrations on reaction rates to the effects of changes in enzyme properties on the same rates. Matrix equations relating the flux control and concentration control coefficients to the elasticity coefficients of enzymes in simple linear and branched pathways incorporating feedback are given, together with their general solutions and a numerical example. These equations allow one to develop rigorous criteria by which to decide the optimal strategy for the improvement of a microbial process. We show how this could be used in deciding which property of which enzyme should be changed in order to obtain the maximal concentration of a metabolite or the maximal metabolic flux.
TL;DR: Bromoperoxidase was shown to be stable under turnover conditions for three weeks at room temperature, catalyzing the bromination of phenol red into bromophenol blue, the first example of an oxidoreductase which displays such great stability.
Abstract: The conversion is described of phenolsulphonephtalein (phenol red) to 3,3',5,5'-tetrabromophenolsulphonephthalein (bromophenol blue) by bromoper-oxidase from the brown alga Ascophyllum nodosum. This reaction provides a convenient assay for the detection of bromoperoxidase activity in vitro. Bromoperoxidase was shown to be stable under turnover conditions for three weeks at room temperature, catalyzing the bromination of phenol red into bromophenol blue. When stored at room temperature in organic sol vents such as acetone, methanol, ethanol [present up to 60% (v/v)], and 1-propanol [40% (v/v)], bromoperoxidase was stable for more than one month. As far as we know this is the first example of an oxidoreductase which displays such great stability. This enhances the applicability of the enzyme in organic synthesis.
TL;DR: In this article, the authors provide a simple relationship among a-amylase activities, which allows comparison of the enzyme activities in the literature, even though the assay methods and definitions of an enzyme unit are different, enzyme activities can be correlated as a function of incubation temperature, incubation time, dilution factor and measurement methods.
Abstract: a-Amylase enzymes (1,4-a-~-glucanohydrolase, E.C.3.2.1.1) catalyze the hydrolysis of a l ,4 glucosidic linkages in polysaccharides of three or more a-I, 4-linked D-glucose units to produce maltose and larger oligosaccharides. 1 ~ 2 Since there are many different assay methods and definitions for a unit of a-amylase enzyme activity, it is almost impossible to compare enzyme activities. One reason is that most groups working with a-amylase developed their own enzyme assay systems, each with its own unit of a ~ t i v i t y . ~ The objective of this communication is to provide a simple relationship among a-amylase activities, which allows comparison of the enzyme activities in the literature. Even though the assay methods and definitions of an enzyme unit are different, enzyme activities can be correlated as a function of incubation temperature, incubation time, dilution factor, and measurement methods. This result will be useful in finding a microorganism or culture conditions which give the highest enzyme activity.
TL;DR: In order to study the anaerobic oxidation of H/sub 2/S by T. denitrificans under constant growth conditions the organism was cultured in a continuous stirred tank reactor to identify any unforeseen problems which might be associated with growth.
Abstract: In order to study the anaerobic oxidation of H/sub 2/S by T. denitrificans under constant growth conditions the organism was cultured in a continuous stirred tank reactor. A series of experiments was conducted having three purposes: 1) to identify any unforeseen problems which might be associated with growth of T. denitrificans on a continuous basis; 2) to examine the effect of metabolic state and environment on the maximum loading of H/sub 2/S; and 3) to examine the relationship between growth rate and yield of biomass per mole H/sub 2/S oxidized.
TL;DR: Rapid liquid‐liquid extraction of lactate dehydrogenase from muscle by using a low‐cost aqueous bipolymer two‐phase system was achieved by using the dye Procion yellow HE‐3G (bound to polyethylene glycol).
Abstract: Rapid liquid-liquid extraction of lactate dehydrogenase from muscle by using a low-cost aqueous bipolymer two-phase system was achieved by using a centrifugal separator. Extraction of the target enzyme into the upper phase was enhanced by including the dye Procion yellow HE-3G (bound to polyethylene glycol). The dye acted as an affinity ligand for the enzyme. The isolation of the enzyme was carried out either by using a cell extract or by homogenizing the muscle directly in the system. The latter approach reduced the preparation time with a factor of 0.25. The two methods gave, respectively, 310 and 360 kU lactate dehydrogenase/kg muscle (measured at 22 degrees C). By using a small centrifugal separator, Alfa Laval LAPX 202, 3-5 kg muscle could be processed/h in a 30-L, two-phase system.
TL;DR: Ethanol fermentation by yeast was carried out in a cell filtration recycle system with a hollow‐fiber membrane filter using 14% glucose feed, with an ethanol productivity and yeast growth rate decreased as the cell concentration increased beyond a certain level.
Abstract: Ethanol fermentation by yeast was carried out in a cell filtration recycle system with a hollow-fiber membrane filter. Maximum biomass concentrations up to 210 g dry wt/L were obtained, but in normal operation concentrations they were between 100 and 150 g/L. The ethanol productivity using 14% glucose feed was 85 g/L h, with an ethanol concentration of 65 g/L and an ethanol yield of over 90%. The ethanol productivity and yeast growth rate decreased as the cell concentration increased beyond a certain level. The cell mass in the reactor was maintained by a proper manipulation of diluticn rate and bleed ratio depending on the growth rate.
TL;DR: Blue–green algae, Spirulina platensis, is cultivated under photoautotrophic growth conditions designed to have nearly uniform growth rate throughout the fermentor by illumination both sides of a rectangular vessel and results show that growth rate and bioenergetic yield are a function of light intensity.
Abstract: Blue-green algae, Spirulina platensis, is cultivated under photoautotrophic growth conditions designed to have nearly uniform growth rate throughout the fermentor by illumination both sides of a rectangular vessel. The results show that growth rate and bioenergetic yield are a function of light intensity. Several kinetic models are considered to express the relationship between growth rate and light intensity.
TL;DR: Experimental and modeling studies were conducted to analyze the dynamic response behavior of a phenol‐oxidizing fixed film using a differential, fluidized‐bed bioreactor in a recycle loop with a well‐mixed reservoir.
Abstract: Experimental and modeling studies were conducted to analyze the dynamic response behavior of a phenol-oxidizing fixed film using a differential, fluidized-bed bioreactor in a recycle loop with a well-mixed reservoir. With the bioreactor at steady state, a pulse of phenol was added to perturb the system, and the phenol concentration was monitored continuously until steady state was again achieved.
The experimental dynamics were compared with a dynamic mathematical model based on diffusion and reaction within the biofilm, liquid mixing, and biofilm growth. Constant-pH experiments could be adequately described using an unstructured, double-Monod kinetic expression with substrate inhibition by phenol.
However, in dynamic experiments without pH control, the pH of the liquid phase dropped, and damped oscillations were observed in the phenol concentration and reaction rate trajectories. Oscillatory solutions could not be induced in the model, even when product inhibition was included, and a linear stability analysis did not reveal tendencies toward instability. The cause of the experimental oscillations remains unknown.
TL;DR: Model media based correlations are found to be applicable to the fermentation processes if the culture medium does not possess a high yield stress.
Abstract: Oxygen transfer rates and gas holdups were measured in mycelial fermentation broths of Chaetomium cellulolyticum and Neurospora sitophila, each cultured in a 1300-L pilot-plant-scale airlift fermentor. These cultures exhibited highly non-Newtonian flow behavior coupled with a substantial decrease in oxygen transfer rates. The volumetric mass transfer coefficients in these cultures were found to be 65-70% lower than those in water. The data were compared with the available correlations obtained for simulated fermentation broths. In general, the data for C. cellulolyticum are in satisfactory agreement with the correlations for the model media but the data for N. sitophila are higher than that predicted by the correlations. Model media based correlations are found to be applicable to the fermentation processes if the culture medium does not possess a high yield stress.
TL;DR: The equation governing the instant uptake of phenol by microorganisms in chemostat in the high conversion range of Phenol can be used to determine the stability range of continuous stirred tank biochemical reactors (CSTBR) utilizing phenol.
Abstract: The specific uptake rate of phenol by washed cells of Pseudomonas putida grown on phenol in steady-state continuous culture at various dilution rates was studied. The Monod-Haldane-type equation was applied to fit the data and the best kinetic parameters were determined by nonlinear least-squares techniques. The values of the kinetic parameters were found to increase monotonically with the phenol concentration in the original chemostat. The relations between the values of kinetic parameters and phenol concentration in the chemostat were described by empirical equations. Then the equation governing the instant uptake of phenol by microorganisms in chemostat in the high conversion range of phenol was proposed. This equation together with the mass balance equations can be used to determine the stability range of continuous stirred tank biochemical reactors (CSTBR) utilizing phenol.
TL;DR: It is proposed in this article that the production of methane by anaerobic fermentation would be the best use of this stream of waste streams from cheese manufacturing plants, especially for small plants.
Abstract: Cheese whey is the main component of waste streams from cheese manufacturing plants. Whey is a high biochemical oxygen demand (BOD) effluent that must be reduced before the streams are sent to the sewer. It is proposed in this article that the production of methane by anaerobic fermentation would be the best use of this stream, especially for small plants. Single-stage fermentation of lactose, the main component of whey, results in a very low pH and a stalled process. Two-phase fermentation will eliminate this problem. The acidogenic stage of fermentation has been studied at pH of between 4 and 6.5. The nature of the main products of the reaction have been found to be pH dependent. Below a pH of 4.5 a gas (CO(2) and H(2)) is produced along with ethanol, acetate, and butyrate. Above a pH of 4.5 no gas was produced, and the liquid products included less ethanol and butyrate and more acetate. A separate study on the conditions for gas formation showed that if the pH dropped for a short time below 4.5 gases were formed at all subsequent pH. This would indicate a change in population distribution due to the period at a low pH. By assuming that the desired products from the acidogenic stage were butyrate, acetate, and no gases, the optimum pH range was found to be between 6.0 and 6.5.