Input Substrate Concentration Research Articles

Model simulations of continuous rotifer cultures

Derived from the Monod-model and regulating principles a regulation model of the rotifer development in chemostats was developed. The model was validated in continuous cultures of Brachionus angularis both in steady-states, when undisturbed, and in transient-states after perturbations by step changes of dilution rate or input substrate concentration. Simulations of the simple model monotonically approached steady-states, but cultures show overshoots and damped oscillations before reaching this state. After introducing time-lags into the model it depends on the size of the time lag if model rotifer densities reach stable steady-state values (at low time lags) or stable limit cycles with periodic oscillations (at high time lags). At even higher time lags chaotic conditions occur in the model with final extinction of the rotifers.

A comparison between the reaction rates in biofilm reactors and free suspended cells bioreactors

A theoretical equation for comparison of the bioreaction rates in a biofilm reactor and in a bioreactor with free suspended cells at different input substrate concentrations and substrate conversions is proposed. The main assumption is that there is no kinetic change after fixation of the cells. Some previously published experimental data are used for verification of this equation. It is shown that difference between the experimental and calculated data is within 19%.

On-line parameter and state estimation of continuous cultivation by extended Kalman filter

The on-line estimation of biomass concentration and of three variable parameters of the non-linear model of continuous cultivation by an extended Kalman filter is demonstrated. Yeast growth in aerobic conditions on an ethanol substrate is represented by an unstructured non-linear stochastic t-variant dynamic model. The filter algorithm uses easily accessible data concerning the input substrate concentration, its concentration in the fermentor and dilution rate, and estimates the biomass concentration, maximum specific growth rate, saturation constant and substrate yield coefficient. The microorganismCandida utilis, strain Vratimov, was cultivated on the ethanol substrate. The filter results obtained with the real data from one cultivation experiment are presented. The practical possibility of using this method for on-line estimation of biomass concentration, which is difficult to measure, is discussed.

Optimization of L-aspartic acid production using immobilized Escherichia coli cells without regard to decay of aspartase activity.

This article describes an efficient production method for L-aspartic acid using aspartase activity of immobilized Escherichia coli cells. The method was examined by use of a rate equation for the aspartase reaction derived on the basis of a one-substrate, one-product mechanism of enzyme reaction. It was found that the reaction temperature must be decreased with the progress of the reaction to obtain higher conversion efficiently near the end of the reaction. In addition, the productivity of L-aspartic acid was found to be increased with an increase in input substrate concentration.

Performance characteristics of a cstr containing immobilised enzyme particles

AbstractThe effects of internal and external substrate diffusion resistances on the performance of a continuous stirred tank reactor are analysed in this work. Both immobilised enzymatic reactions with and without substrate inhibitions are considered. The substrate conversion for the reaction without substrate inhibition is dependent on four dimensionless parameters: the Thiele modulus, the dimensionless Michaelis constant, the mass transfer Nusselt number and β, which represents a combination of particle hold‐up, maximum reaction rate, input substrate concentration and substrate residence time in the continuous stirred tank reactor. For the corresponding reaction with substrate inhibition, the effect of the additional dimensionless inhibition constant on the substrate conversion is also very significant. The substrate conversion generally decreases with decrease in dimensionless parameter β, increase in Thiele modulus and decrease in mass transfer Nusselt number. For the reaction with small Thiele modulus, β and strong substrate diffusion resistances, a multireactor system may be needed if a certain desired substrate conversion is required. The single CSTR model can be extended to describe the multireactor system and the effect of the number of reactors on the substrate conversion for a two‐ or more reactor system is also examined.

Theoretical studies on the coexistence of competing species under continuous-flow conditions

In continuous-flow environments, such as a chemostat, we find that, in theory, stable mixed populations of competing species obeying Monod/Michaelis-Menten growth kinetics (extended to more than one limiting substrate) cannot coexist unless the number of growth-limiting substrates is equal to or greater than the number of species. Additional restrictions on the relative values of the growth-yield constants and input-substrate concentrations must also be satisfied. Examples of the theoretical growth of mixed cultures after initial inoculation in stable and unstable cases are presented. The ecological consequences of these findings are briefly discussed.

Study of the dynamic behavior of the chemostat system

AbstractThis paper deals with a theoretical study on the dynamic, character of the chemostat system. It. is primarily based on the Monod model for growth limitation, although certain more complex models are considered. Since the Monod model is described in terms of two variables, an analysis by use of a phase plane plot will show the various possible types of behavior theoretically expected for transient conditions of the system. In this paper it will be shown that the chemostat system might show an overshoot (or an underswing) with respect to changes in cell and substrate concentrations, depending on the extent to which the system might be disturbed from steady‐slate conditions. Other types of transient behavior ran also be expected when one of the system parameters such as dilution rate or input substrate concentration is disturbed in a stepwise manner. The simple Monod chemostat model was found never to oscillate in either a damped or a sustained manner as has been experimentally reported. Discussion is included about the transient behavior of other chemostat models such as that involving a variable yield coefficient, i.e., including the effect of cell maintenance requirements.