Monod Constant Research Articles

Batch Kinetics and Effects of Process Parameters for Biodegradation of Reactive Black 5 in an Aerobic Mixed Microbial Culture

Mixed microbial culture used in this study was developed from sludge that was taken from local textile wastewater treatment tank. Acclimatization process was performed before starting the biodegradation experiment to obtain a microbial culture with high degradation properties. Kinetic studies by the mixed microbial culture were determined quantitatively for the model pollutant, Reactive Black 5 (RB 5). By using Michaelis-Menten model, the constants were found to be 11.15 mg L-1 h-1 and 29.18 mg L-1 for V m and Km respectively. The values of kinetic constants for Monod model were found to be 33.11 mg L-1 cell h-1 for the maximum specific microbial growth rate, µm and 86.62 mg L-1 for Monod constant, K5. The effects of process parameters such as pH, inoculum size and initial dye concentration on the biodegradation of azo dye, RB 5 were systematically investigated. Maximum removal efficiencies observed in this study were 75% for pH 6, I 00% for 15% inoculum concentration and 75% for 20 ppm of initial dye concentration.

Batch Kinetics and Effects of Process Parameters for Biodegradation of Reactive Black 5 in an Aerobic Mixed Microbial Culture

Mixed microbial culture used in this study was developed from sludge that was taken from local textile wastewater treatment tank. Acclimatization process was performed before starting the biodegradation experiment to obtain a microbial culture with high degradation properties. Kinetic studies by the mixed microbial culture were determined quantitatively for the model pollutant, Reactive Black 5 (RB 5). By using Michaelis-Menten model, the constants were found to be 11.15 mg l-1 h-1 and 29.18 mg l-1 for Vm and Km respectively. The values of kinetic constants for Monod model were found to be 33.11 mg l-1 cell h-1 for the maximum specific microbial growth rate, µm and 86.62 mg l-1 for Monod constant, Ks. The effects of process parameters such as pH, inoculum size and initial dye concentration on the biodegradation of azo dye, RB 5 were systematically investigated. Maximum removal efficiencies observed in this study were 75% for pH 6, 100% for 15% inoculum concentration and 75% for 20 ppm of initial dye concentration.

Kinetic Investigation In Lactic Acid Production By L. Acidophilus

Lactic acid is a natural organic acid, which is used in chemical, textile, pharmaceuticals, and food industries. Commercial lactic acid is being produced by fermentation of carbohydrate by using lactic acid bacteria. The purpose of this study is to calculate the following kinetic parameters: the maximum specific growth rate , the Monod constant , and the product yield coefficient in the process of production lactic acid from glucose by Lactobacillus Acidophilus, which is a homolactic acid bacteria.Several batch fermentations at glucose concentration range from 9.3 g/L to 151.2 g/L were performed at optimum condition at 37 oC and pH = 6.5. When increasing glucose concentration, value of maximum specific growth rate reduced, thus non-competitive inhibition exists. The maximum specific growth rate was 0.289 hr-1, substrate inhibition constant was 133 ± 3.2 g/L and KS = 0.8 g/L. Yield of product was decreasing from 0.81 to 0.63 when increasing initial concentration. For scale-up process, the initial glucose concentration should not excess 90g/L.

Kinetic Modeling and Isotopic Investigation of Isobutanol Fermentation by Two Engineered Escherichia coli Strains

We constructed an Escherichia coli BL21 strain with the Ehrlich pathway (the low-performance strain for isobutanol production). We also obtained a high isobutanol-producing E. coli strain JCL260 from the James Liao group (University of California). To compare the fermentation performances of the two engineered strains, we employed a general Monod-based model coupled with mixed-growth-associated isobutanol formation kinetics to simulate glucose consumption, biomass growth, and product secretion/loss under different cultivation conditions. On the basis of both kinetic data and additional 13C-isotopic investigation, we found that the low-performance strain demonstrated robust biomass growth in the minimal growth medium (20 g/L glucose), achieving isobutanol production (up to 0.95 g/L). It utilized significant amounts of yeast extract to synthesize isobutanol when it grew in the rich medium. The rich medium also enhanced waste product secretion, and thus reduced the glucose-based isobutanol yield. In contrast, JCL260 had poor biomass growth in the minimal medium due to an inflated Monod constant (KS), while the rich medium greatly promoted both biomass growth and isobutanol productivity (∼60% of the theoretical isobutanol yield). With the optimized keto-acid pathway, JCL260 synthesized isobutanol mostly from glucose even in the presence of sufficient yeast extract. This study not only provided a kinetic model for scaled-up isobutanol fermentation but also offered metabolic insights into the performance trade-off between the two engineered E. coli strains.

Approximate analytical solution of the concentration of phenol and oxygen and rate of phenol degradation in fluidized bed bioreactor

A theoretical model for fluidized bioreactor (FBR) is presented. The model is based on system of reaction-diffusion equation containing a non-linear term related to specific growth rate of biomass. Homotopy analysis method (HAM) is successfully employed in the development of non-linear steady state phenol degradation. In this paper simple and approximate polynomial expression of concentration of phenol and oxygen and rate of phenol degradation are derived for all possible values of parameters ϕO (dimensionless modulus for oxygen), ϕS (dimensionless modulus for phenol), Ki* (dimensionless inhibition constant for phenol) and KO*, KS* (dimensionless monod constant for oxygen and phenol). The limiting case results are compared with our common results and are found to be in good agreement.

A fundamental analysis of continuous flow bioreactor and membrane reactor models with non-competitive product inhibition. III. Linear inhibition

The steady-state production of a product produced through the growth of microorganisms in a continuous flow bioreactor is presented. A generalised reactor model is used in which both the classic well-stirred bioreactor and the idealised membrane bioreactor are considered as special cases. The reaction is assumed to be governed by Monod growth kinetics subject to non-competitive product inhibition. Inhibition is modelled as a decreasing linear function of the product concentration with a finite cut-off. This reaction scheme is well documented in the literature, although a stability analysis of the governing equations has not previously been presented. The steady-state solutions for the models have been obtained, and the stability has been determined as a function of the residence time. The key dimensionless parameter (γ) that controls the degree of non-competitive product inhibition is obtained by scaling of the equations, and its effect on the reactor performance is quantified in the limit when product inhibition is ‘small’ and ‘large’. The parameter γ is the reciprocal of a scaled inhibition constant (Pm) that depends upon the substrate and product yield factors and the Monod constant (). © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Growth kinetic parameters and biosynthesis of polyhydroxybutyrate in Cupriavidus necator DSMZ 545 on selected substrates

Kinetic model for Cupriavidus necator in batch culture using glucose, fructose and molasses as carbon sources was obtained. The experimental data was also fitted with the modified logistic equation that can provide adequate description for PHB synthesized by C. necator. The lineweaver-Burk plot defined biokinetic coefficients which were described by a simplified Monod?s rate model. The specific growth rates, ?max and the Monod constants, Ks, for various substrates such as glucose, fructose and molasses were 0.18, 1.25, 0.42 h-1 and 107.53, 30.342, 188.16 g/l, respectively. The kinetic constants were evaluated on the basis of non-linear regression were solved using MATLAB software. A good agreement was found between the experimental and the predicted values, which indicated that the model with differential equations would describe fermentation process for the PHB formation.

A fundamental analysis of continuous flow bioreactor and membrane reactor models with non‐competitive product inhibition. II. Exponential inhibition

AbstractThe steady‐state production of a product produced through the growth of microorganisms in a continuous flow bioreactor is presented. A generalised reactor model is used in which both the classic well‐stirred bioreactor and the idealised membrane bioreactor are considered as special cases. The reaction is assumed to be governed by Monod growth kinetics subject to non‐competitive product inhibition. Inhibition is modelled as a decaying exponential function of the product concentration. This reaction scheme is well documented in the literature, although a stability analysis of the governing equations has not previously been presented. The performance of a well‐stirred bioreactor with microorganisms death is also not currently available in the literature. The steady‐state solutions for the models have been obtained, and the stability has been determined as a function of the residence time. The key dimensionless parameter (γ) that controls the degree of non‐competitive product inhibition is obtained by scaling of the equations, and its effect on the reactor performance is quantified in the limit when product inhibition is ‘small’. The parameter γ is a scaled inhibition constant (Kp) that depends upon the substrate and product yield factors and the Monod constant ($\gamma = {\alpha_{s}\over \alpha_{p}} \cdot {K_{s}\over K_{p}}$). Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Acid phosphatase production by Rhizopus delemar: A role played in the Ni(II) bioaccumulation process

The microbial growth and activity of acid phosphatase enzyme during the growth of Rhizopus delemar in the presence or absence of Ni(II) ions were investigated. An increase in initial Ni(II) ion concentration inhibited both growth rate of R. delemar and acid phosphatase activity. The maximum-intrinsic specific growth rate (μm) and Monod constant (Ks) of microorganism in Ni(II)-free medium were found as 0.0649h−1 and 1.8928g/L, respectively. The inhibition of Ni(II) ions on growth rate of R. delemar was found to be a competitive inhibition and the inhibition constant was found to be 67.11mg Ni(II)/L. The intrinsic Michaelis–Menten constant (Km) and maximum forward velocity of the reaction (vm) were determined as 3.17mM and 833.3μmol/Lmin, respectively, in Ni(II)-free medium. In the presence of Ni(II) ions, the activity of acid phosphatase was inhibited. Addition of Ni(II) ions decreased the maximum reaction velocity, vm, showed noncompetitive-type inhibition kinetics and the inhibition constant was determined as 50mg Ni(II)/L. Maximum Ni(II) uptake was obtained by the growing cells of R. delemar, while the uptake capacity of resting cells was lowest. This study proved that acid phosphatase enzyme participated in the Ni(II) bioaccumulation mechanism of growing R. delemar.

Butler–Volmer–Monod model for describing bio-anode polarization curves

A kinetic model of the bio-anode was developed based on a simple representation of the underlying biochemical conversions as described by enzyme kinetics, and electron transfer reactions as described by the Butler-Volmer electron transfer kinetics. This Butler-Volmer-Monod model was well able to describe the measured bio-anode polarization curves. The Butler-Volmer-Monod model was compared to the Nernst-Monod model described the experimental data significantly better. The Butler-Volmer-Monod model has the Nernst-Monod model as its full electrochemically reversible limit. Contrary to the Nernst-Monod model, the Butler-Volmer-Monod model predicts zero current at equilibrium potential. Besides, the Butler-Volmer-Monod model predicts that the apparent Monod constant is dependent on anode potential, which was supported by experimental results.

Kinetic model for polyhydroxybutyrate (PHB) production by Hydrogenophaga pseudoflava and verification of growth conditions

A kinetic model that describes microbial growth, biopolymer production and substrate consumption is used to predict the performance of batch fermentation ofHydrogenophaga pseudoflava. H. pseudoflava DSMZ 1034 is useful in synthesizing polyhydroxyalkanoates (PHAs).The experimental data was also fitted with the logistic equation that can provide adequate description for PHA synthesized by H. pseudoflava. The Lineweaver-Burk plot defined biokinetic coefficients which were described by a simplified Monod’s rate model. The specific growth rates, μmax and the Monod constants, Ks, for various substrates such as glucose, fructose were 0.36, 0.24, h-1 and 106, 80 g/l, respectively. A good agreement was found between the experimental and the predicted values, which indicated that the model with differential equations would describe fermentation process for the PHA formation. Key words: Kinetic model, polyhydroxyalkanoates, Hydrogenophaga pseudoflava,logistic model, Monod, biopolymer.

Determination of kinetic parameters of growth and carotenogenesis in the red yeast Xanthophyllomyces dendrorhous

Glucose-limited continuous culture experiments with Xanthophyllomyces dendrorhous ATCC 24202 were carried out in a 2.5 L jar fermentor at 20°C and pH 4.5. A reciprocal plot of the steady-state data at a dilution rate of 0.037∼0.096 h−1 was used to estimate a maximum specific growth rate constant of 0.11 h−1 and a Monod constant of 260 mg/L. The degree of carotenogenesis in X. dendrorhous was also investigated in terms of the residence time, which is the reciprocal of the dilution rate. The carotenoid content related to the residence time appeared to assume a typical form of saturation kinetics. The maximum carotenoid content for the strain was estimated to be 0.6 μg/mg dry cell weight. The saturation constant, which was tentatively defined in this work, was found to be 7.2 h.

Control of specific growth rate in Saccharomyces cerevisiae

In this contribution we resolve the long-standing dispute whether or not the Monod constant (K(S)), describing the overall affinity of an organism for its growth-limiting substrate, can be related to the affinity of the transporter for that substrate (K(M)). We show how this can be done via the control of the transporter on the specific growth rate; they are identical if the transport step has full control. The analysis leads to the counter-intuitive result that the affinity of an organism for its substrate is expected to be higher than the affinity of the enzyme that facilitates its transport. Experimentally, we show this indeed to be the case for the yeast Saccharomyces cerevisiae, for which we determined a K(M) value for glucose more than two times higher than the K(S) value in glucose-limited chemostat cultures. Moreover, we calculated that at glucose concentrations of 0.03 and 0.29 mM, the transport step controls the specific growth rate at 78 and 49 %, respectively.

A study on the inhibition kinetics of bioaccumulation of Cu(II) and Ni(II) ions using Rhizopus delemar

The microbial growth and simultaneous bioaccumulation of Cu(II) and Ni(II) ions during the growth of Rhizopus delemar in molasses medium was investigated in a batch system. The level of Cu(II) and Ni(II) bioaccumulation and microbial growth was dependent on pH, molasses sucrose concentration and initial Cu(II) and Ni(II) ion concentrations. An increase in initial total metal ion concentration inhibited both the growth rate of fungus and the bioaccumulation capacity. Lineweaver–Burk plot of Monod equation was used to study the inhibition kinetics of bioaccumulation of Cu(II) and Ni(II) and the intrinsic and apparent model parameters were evaluated in metals-free and metals-contaminated fermentation media. The maximum specific growth rate ( μ m) and the Monod constant ( K s) of microorganism in metals-free media were found as 0.405 L/h and 3.977 g/L, respectively. As μ m remained constant in the presence of increasing concentrations of Cu(II) and Ni(II) ions, the combined inhibition of Cu(II) and Ni(II) ions on the growth rate of R. delemar was found to be a competitive inhibition. The inhibition constants for Cu(II) and Ni(II) ions were determined as 56.71 mg Cu(II)/L and 47.44 mg Ni(II)/L. As the bioaccumulation of Cu(II) and Ni(II) ions was reduced by the presence of increasing concentrations of the other metal ion, compared with the single-metal systems, the individual action of Cu(II) and Ni(II) ions on the bioaccumulation of R. delemar was generally found to be antagonistic. On the other hand, the total combined effects of Cu(II) and Ni(II) ions on the bioaccumulation of R. delemar are thought to be synergistic since the total bioaccumulated metal ion quantities per unit mass of biomass were higher than those obtained in the growth media containing Cu(II) and Ni(II) ions alone at the same concentrations.

Diffusion and Monod kinetics to determine in vivo human corneal oxygen‐consumption rate during soft contact‐lens wear

The rate of oxygen consumption is an important parameter to assess the physiology of the human cornea. Metabolism of oxygen in the cornea is influenced by contact-lens-induced hypoxia, diseases such as diabetes, surgery, and drug treatment. Therefore, estimation of in vivo corneal oxygen-consumption rate is essential for gauging adequate oxygen supply to the cornea. Phosphorescence quenching of a dye coated on the posterior of a soft contact lens provides a powerful technique to measure tear-film oxygen tension (Harvitt and Bonanno, Invest Ophthalmol Vis Sci 1996;37:1026-1036; Bonanno et al., Invest Ophthalmol Vis Sci 2002;43:371-376). Unfortunately, previous work in establishing oxygen-consumption kinetics from transient postlens tear-film oxygen tensions relies on the simplistic assumption of a constant corneal-consumption rate. A more realistic model of corneal metabolism is needed to obtain reliable oxygen-consumption kinetics. Here, physiologically relevant nonlinear Monod kinetics is adopted for describing the local oxygen-consumption rate, thus avoiding aphysical negative oxygen tensions in the cornea. We incorporate Monod kinetics in an unsteady-state reactive-diffusion model for the cornea contact-lens system to determine tear-film oxygen tension as a function of time when changing from closed-eye to open-eye condition. The model was fit to available experimental data of in vivo human postlens tear-film oxygen tension to determine the corneal oxygen-consumption rate. Reliance on corneal oxygen diffusivity and solubility data obtained from rabbits is no longer requisite. Excellent agreement is obtained between the proposed model and experiment. We calculate the spatial-averaged in vivo human maximum corneal oxygen-consumption rate as Q(c)(max) = 1.05 x 10(-4) mL/(cm(3) s). The calculated Monod constant is K(m) = 2.2 mmHg.

Voltammetric characterization of the aerobic energy-dissipating nitrate reductase of Paracoccus pantotrophus: exploring the activity of a redox-balancing enzyme as a function of electrochemical potential

Paracoccus pantotrophus expresses two nitrate reductases associated with respiratory electron transport, termed NapABC and NarGHI. Both enzymes derive electrons from ubiquinol to reduce nitrate to nitrite. However, while NarGHI harnesses the energy of the quinol/nitrate couple to generate a transmembrane proton gradient, NapABC dissipates the energy associated with these reducing equivalents. In the present paper we explore the nitrate reductase activity of purified NapAB as a function of electrochemical potential, substrate concentration and pH using protein film voltammetry. Nitrate reduction by NapAB is shown to occur at potentials below approx. 0.1 V at pH 7. These are lower potentials than required for NarGH nitrate reduction. The potentials required for Nap nitrate reduction are also likely to require ubiquinol/ubiquinone ratios higher than are needed to activate the H(+)-pumping oxidases expressed during aerobic growth where Nap levels are maximal. Thus the operational potentials of P. pantotrophus NapAB are consistent with a productive role in redox balancing. A Michaelis constant (K(M)) of approx. 45 muM was determined for NapAB nitrate reduction at pH 7. This is in line with studies on intact cells where nitrate reduction by Nap was described by a Monod constant (K(S)) of less than 15 muM. The voltammetric studies also disclosed maximal NapAB activity in a narrow window of potential. This behaviour is resistant to change of pH, nitrate concentration and inhibitor concentration and its possible mechanistic origins are discussed.

Exploring optimal environmental factors for fermentative hydrogen production from starch using mixed anaerobic microflora

Our previous work demonstrated that an acclimated mixed bacterial consortium was able to produce H 2 from sugar substrates. To reduce the medium cost for more commercially viable H 2 production, cassava starch was used as the feedstock to produce H 2 via dark fermentation. Three factors, namely, temperature, pH and starch concentration ( C starch ) , were intensively examined for their effects on H 2 production activity. The H 2 production kinetics was determined using a Monod-type kinetic model. The results show that mesophilic temperature ( 37 ∘ C ) is preferable for H 2 production with the H 2 -producing sludge used. The H 2 production efficiency and the composition of soluble metabolites were found to be highly sensitive to the change in pH, as pH 6.0 seemed to give the best overall H 2 production performance. In a non-pH-controlled culture (initial pH = 8.5 ), ethanol and butyrate were the major soluble metabolites, whereas the predominant metabolites switched to butyrate alone (accounting for 70–80% of total soluble microbial products) when the culture pH was controlled at a fixed level ranging from 5.5 to 7.0. Meanwhile, the maximum H 2 production rate occurred when the initial starch concentration was 24 g COD/l. The dependence of H 2 production rate on starch concentration could be described by using Monod-type model and the predicted kinetic constants, namely, maximum H 2 production rate ( v max , H 2 ) and Monod constant ( K s ) , were 1741 ml/h/l and 16.28 g COD/l, respectively. Under the optimal conditions ( 37 ∘ C , pH 6.0, C starch = 24 g COD / l ), the H 2 production rate increased to 1119 ml/h/l, while a high H 2 yield of 9.47 mmol H 2 /g starch was obtained. This performance appeared to be superior to that obtained from other starch-to-bio H 2 systems reported in the literature.

Effect of liquid distribution on the organic removal in a trickle bed filter

Abstract The effect of liquid distribution on the biological removal of propylene glycol methyl ether (PGME) in a trickle bed filter was investigated using a 0.3 m diameter column filled with 2-cm plastic spheres. Various liquid flowrates, bed heights (the ratio of bed height to bed diameter H / D = 2.3 and 4.6) and initial concentrations of PGME were used in experiments. The effect of initial liquid distribution was also examined using the multipoint (MPD) and single-point liquid distributors (SPD). The effect of liquid flow rate on liquid distribution, and hence, the BOD 5 removal was found more significant for the short bed ( H / D = 2.3). The BOD 5 removal using MPD increased about 29% when the liquid flow rate was increased from 0.184 to 0.918 kg m −2 s −1 . On the other hand, for H / D = 4.6 with both MPD and SPD, the effect of liquid flowrate on the BOD 5 removal was insignificant although the dynamic liquid hold-up increased about two fold. It was also found that local distribution of the BOD 5 removal corresponded well with local liquid distribution in the bed. In addition, a 37% decrease in the percentage BOD 5 removal was observed while the BOD 5 removal amount increased from 62 to 211 mg L −1 with increases in the initial concentration from 100 to 500 ppm. Based on the Monod kinetic model, the maximum BOD 5 removal rate in the trickle bed filter was found to be 11.7 mg L −1 h −1 and the Monod constant was 759 mg L −1 .

Mathematical analysis of the whole core injection method accuracy for measuring phenanthrene biodegradation rates in undisturbed marine sediments

Rates of 14C-phenanthrene mineralization in contaminated, undisturbed marine sediments were measured using the whole core injection method to assess microbial natural attenuation activity as a function of sediment depth. Submerged sediments were sampled from Eagle Harbor, a marine superfund site in Puget Sound. Experiments show significant biodegradation activities (0.0012-0.0036 day(-1)) in the sediment horizons from 0 to 10 cm. The purpose and scope of this paper is to evaluate the range of experimental conditions giving valid results; a mathematical simulation described competing contaminant 14C-phenanthrene diffusion and simultaneous biodegradation (Monod kinetics), both retarded by sorption. The effect of aging was examined with two sorption models in presumed pseudo-homogenous sediments having effective properties. The simulation predictions provide quantitative guidelines for the successful use of the whole core injection method. (1) The effective Monod constant KS' in sediment is increased by a large partition coefficient KP between sediment and water and makes the apparent 14C-phenanthrene biodegradation approach first-order kinetics. (2) When KS'>1 mg(-1) l(-1), the measured 14C-phenanthrene biodegradation extent is biased by inadequately distributed injected tracer only when less than 7% of the sediment horizon is initially probed and mixed with injected tracer. (3) A short incubation time (<20 days) is necessary when a mobile indicator, e.g., gaseous 14CO2, is used. For longer incubation times, predictions show that a 14CO2 indicator diffuses to adjacent horizons, thus smearing the depth profile of biodegradation. (4) This method employing a radiolabeled tracer provides accurate biodegradation rates for freshly contaminated sediments, and represents an upper limit to the natural phenanthrene biodegradation extents if the contaminant is aged over 50 days.

Overview of some theoretical approaches for derivation of the Monod equation

The Monod equation has been widely applied to describe microbial growth, but it has no mechanistic basis and is purely empirical. Extensive efforts have been dedicated to develop theoretical approaches for derivation of the Monod equation, which can be classified into three major groups, i.e., kinetic, thermodynamic, and substance transport approaches. In this review, four representative approaches are thus discussed. Due to the fact that different assumptions are made in each approach, no universal physical meaning of the Monod constant (K (s)) can be revealed. However, it seems that the Monod constant would be free energy-dependent and have nonequilibrium thermodynamic characteristics.